What is normal blood pressure for a 2 year old? How is high blood pressure diagnosed in kids? What are the causes and signs of hypertension in children? Explore these questions and more in our in-depth article.

Defining Normal Blood Pressure in Children

There is no single “normal” blood pressure value that applies to all children. A child’s healthy blood pressure depends on their age, height, and gender. For children under 13, pediatricians use a percentile chart to compare a child’s blood pressure to their peers of the same age, height, and gender. A child is considered to have elevated blood pressure if their readings fall above the 90th percentile, and hypertension if above the 95th percentile.

Once a child reaches 13 years old, the normal blood pressure ranges are the same as those used for adults:

• Normal blood pressure: Less than 120/80 mm Hg
• Elevated blood pressure: Systolic (top number) between 120-129 mm Hg and diastolic (bottom number) less than 80 mm Hg
• Hypertension: Top or bottom number higher than 130/80 mm Hg

How is a Child’s Blood Pressure Checked?

A child’s blood pressure should be checked annually starting at age 3, during their routine well-child visit. The child should sit comfortably with their feet supported and their arm level with their heart. The pediatrician or nurse will use a stethoscope and an inflated arm cuff to measure the blood pressure.

If a child has a health condition that increases their risk of high blood pressure, such as obesity or kidney disease, their blood pressure will be checked at every doctor visit. Additionally, if a child’s blood pressure is high during a well-child check, it will be monitored more frequently to identify any trends.

Causes of High Blood Pressure in Children

There are several potential causes of high blood pressure in children, including:

• Obesity or being overweight
• High-sodium diet (too much salt)
• Kidney disease
• Congenital or acquired heart disease
• Thyroid or adrenal disease
• Diabetes
• Genetic disorders (inherited from a parent or grandparent)
• Stress

When a young child (under 6) has high blood pressure, the cause is often a related medical condition, such as kidney disease. This is called secondary hypertension. Primary hypertension, which has no disease-related cause, is more common in older children and teens and is often linked to obesity.

Recognizing the Signs of High Blood Pressure in Children

Hypertension in children is often a silent condition, with no obvious symptoms to alert parents. Typically, high blood pressure is discovered during a routine check-up. However, some children with high blood pressure may experience:

• Frequent headaches
• Changes in vision
• Dizziness

If your child complains of these symptoms, it’s important to contact their pediatrician.

Diagnosing and Monitoring High Blood Pressure in Children

If a child’s pediatrician notices a trend of high blood pressure readings, they may recommend further testing or refer the child to a specialist. One common tool used is a 24-hour portable blood pressure monitoring device, called an ambulatory blood pressure monitor (ABPM). This device can provide a complete picture of a child’s blood pressure throughout the day and night, helping the pediatrician determine if the child needs additional treatment.

Keeping Children’s Blood Pressure Healthy

Regular blood pressure screenings are crucial for identifying high blood pressure in children. If a child’s blood pressure is found to be elevated or hypertensive, their pediatrician may recommend lifestyle changes, such as:

• Encouraging a healthy, low-sodium diet
• Promoting regular physical activity
• Helping the child manage stress

In some cases, medication may also be prescribed to help control high blood pressure. By working closely with their pediatrician, parents can help ensure their child’s blood pressure remains within a healthy range.

Conclusion

High blood pressure in children is a serious condition that, if left untreated, can lead to serious health complications. Regular blood pressure screenings, early detection, and proactive management are key to keeping children’s blood pressure under control. By understanding the causes, signs, and diagnostic process for childhood hypertension, parents can work with their pediatrician to ensure their child’s cardiovascular health remains on track.

High Blood Pressure in Kids – Children’s Health

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You may think that hypertension, or high blood pressure, is a condition that affects only adults. However, according to the American Academy of Pediatrics (AAP), an estimated 3.5% of children and teens have high blood pressure. When left untreated, this condition can cause serious complications, such as heart disease, kidney failure, stroke and vision loss.

“A blood pressure reading measures the force of blood against the walls of arteries. This pressure is what your heart has to pump against to get blood out to the rest of your body,” explains Alan Sing, M.D., a pediatric cardiologist at Pediatric Heart Specialists, a Children’s Health℠ Care Network Partner. “If blood pressure is higher, then the heart has to work harder. Over time, this high blood pressure can cause damage to different organ systems in the body.”

However, regular screenings can help identify high blood pressure in children. Learn more about what is considered high blood pressure for a child and ways you can help keep your child healthy.

How is a child’s blood pressure checked?

A child’s blood pressure should be checked once a year at their annual exam starting at the age of 3. Your child should sit comfortably in a chair with their feet supported and their arm level with their heart. Your child’s physician or nurse will use a stethoscope and a hand-inflated arm cuff to check their blood pressure.

If a child has a health condition that increases their risk for high blood pressure, such as obesity or kidney disease, their blood pressure will be checked at every doctor visit. If a child’s blood pressure is high at a well-child visit, their blood pressure will also be checked more frequently.

Your child’s pediatrician will track trends in blood pressure over time, not just the initial screening, to accurately identify a diagnosis of hypertension.

What is a normal blood pressure for a child?

There isn’t one single number or blood pressure that is considered normal for all children. A healthy blood pressure for a child depends on their age, height and gender.

For children under the age of 13, your pediatrician will use a percentile chart to compare your child’s blood pressure to peers of the same age, height and gender. This allows a more precise indication if a young child is showing high blood pressure. A child is considered to have an elevated blood pressure if their blood pressure falls above the 90th percentile, and hypertension if they are above the 95th percentile.

Over the age of 13, normal blood pressure ranges are the same for teenagers as they are for adults:

• Normal blood pressure: Less than 120/80 mm Hg
• Elevated blood pressure: Systolic (top number) between 120-129 mm Hg and diastolic (bottom number) less than 80 mm Hg
• Hypertension: Top or bottom number higher than 130/80 mm Hg

If your child’s pediatrician notices a trend of high blood pressure readings, they will closely monitor your child’s blood pressure or refer you to a specialist to address any health concerns. They may have your child wear a 24-hour, portable blood pressure monitoring device (called an ambulatory blood pressure monitor or ABPM). This can be worn at home during your child’s normal routine and takes measurements every 20 to 30 minutes during the daytime and 30 to 60 minutes at night.

This monitor can help your child’s pediatrician decide whether your child needs further tests or treatment by giving a complete picture of blood pressure throughout the day and night.

What are signs of high blood pressure in kids?

Hypertension is often a silent condition. Typically, there aren’t obvious symptoms to let parents know their child has high blood pressure; it is often diagnosed when the doctor discovers it during an exam. This is why regular blood pressure screening is so important.

Some children with high blood pressure may experience frequent headaches, changes in vision or dizziness. If your child complains of these symptoms, contact your pediatrician.

What are causes of high blood pressure in kids?

A child’s blood pressure might be high when it is measured for many reasons, such as stress, illness, recent physical activity, a true hypertension issue or a medical condition.

Causes of high blood pressure in kids can include:

• Obesity or being overweight
• High-sodium diet (too much salt)
• Kidney disease
• Congenital or acquired heart disease
• Thyroid or adrenal disease
• Diabetes
• Genetic disorders (inherited from a parent or grandparent)
• Stress

When a young child (under 6) has high blood pressure, the cause is often a related medical condition, such as kidney disease. This is called secondary hypertension.

When high blood pressure has no disease-related cause, it’s called primary hypertension. Primary hypertension is more common in older children and teens and is commonly related to obesity or to a family history of hypertension.

“There is a growing trend in the number of children and teens who are overweight or have obesity, and this is a major cause of high blood pressure in kids,” says Smitha Vidi, M.D., a pediatric nephrologist at Children’s Health and Assistant Professor at UT Southwestern. “Additionally, kids are eating a lot of processed foods, which have very high amounts of salt. A high-salt diet is a big contributor to increasing blood pressures.”

How is high blood pressure treated in children?

If your child is diagnosed with hypertension, your pediatrician may recommend certain lifestyle changes to lower their blood pressure, such as a healthy diet, regular exercise or weight loss.

• DASH diet: Designed from research sponsored by the National Institutes of Health, the DASH diet focuses on eating fruits, vegetables, low-fat dairy, nuts, beans and seeds.
• Exercise: The AAP recommends children and adolescents get 60 minutes or more of physical activity daily (includes outside play and team sports).
• Low-sodium diet: Sodium is the scientific name for the salt in food. In addition to watching table salt usage, be cautious of how much processed food your child eats.

If needed, your child’s physician may prescribe medications to control blood pressure. These medicines are the same ones adults take, just in age and weight-appropriate doses. Your child’s physician can choose the best medication for your child based on their individual health profile and risk factors.

You can help your child prevent high blood pressure and complications. Talk about the importance of a healthy lifestyle and continue to be a good role model – making healthy food choices and engaging in exercise as a family.

“Taking steps as a family to stay healthy is key to preventing hypertension in children,” says Dr. Vidi. “Try to devote a little of your time each day to doing fun activities with your kids, such as biking, dancing, swimming or even walking to a nearby park. “

Learn more

No matter the reason behind a child having high blood pressure, Children’s Health can provide expert, multidisciplinary care. Learn more about hypertension in kids and how we can help.

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American Academy of Pediatrics, determinants of health, diet, heart health, hypertension, obesity, overweight, primary care

Pediatric Vital Signs & What They Tell You – Cleveland Clinic

It’s like a parental reflex. Your child says, “I don’t feel good,” and your hand shoots out to feel their forehead. As a parent or caregiver, you’re always on the lookout for changes in your child’s health. 

Temperature is one of your child’s vital signs you’ve probably measured at home. Pediatricians check it, too. The other vital signs are blood pressure, heart rate and respiration rate.  

Each of these four vital signs gives info about your child’s basic body functions. Vital signs outside the normal range can point to an illness or health issue. 

Pediatrician Amy Sniderman, MD, explains what these measurements mean and outlines normal pediatric vital signs for children of all ages. 

Normal pediatric vital signs chart 

What are vital signs? 

The four basic vital signs are: 

• Body temperature.  
• Blood pressure. 
• Heart rate. 
• Respiratory (breathing) rate. 

Healthcare providers check these during exams to get a snapshot of your child’s overall health.  

The normal range for pediatric vital signs can vary quite a lot depending on your child’s age and other factors. For instance, the normal infant heart rate is much higher than the normal heart rate for a 12-year-old. 

You can check your child’s vital signs at home. But Dr. Sniderman assures you that you typically don’t need to.  

“Generally, parents don’t need to monitor their children’s vital signs. They’re usually only a concern if your child isn’t feeling well, and vital signs are also out of the healthy range.”

Vital signs definitions 

So, what do all these vital signs mean? 

What is body temperature? 

A part of the brain called the hypothalamus regulates body temperature, which usually doesn’t vary much unless your child is sick.  

You’ve probably measured your child’s temperature at home with a thermometer. There are several different types of thermometers, and it’s important to use them correctly to get an accurate reading. Follow the instructions that came with the thermometer. 

What is blood pressure? 

Blood pressure is one measure of heart health. It measures the force of blood pushing against the inner walls of the arteries as your heart pumps. 

Blood pressure is always given as two numbers: systolic and diastolic.  

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• Systolic pressure is the first or top number in the measurement. It represents the artery pressure when your heart beats.  
• Diastolic pressure is the second or bottom number. It’s the pressure against the arteries in between beats when your heart rests. 

You need a blood pressure cuff to measure your child’s blood pressure at home. But there’s usually no reason to measure your child’s blood pressure beyond their pediatric appointments.  

What is heart rate? 

Heart rate is the number of times your heart beats per minute. You can find your child’s pulse and then count the number of beats in one minute to get their heart rate. 

What is respiratory rate? 

Similar to heart rate, respiratory rate is the number of breaths you take per minute. To find your child’s respiratory rate, you can either: 

• Count their number of breaths in one minute. 
• Count their number of breaths in 30 seconds and multiply that number by two. 

Normal body temperature in children 

A normal body temperature for a child of any age is 98.6 degrees Fahrenheit (or 37 degrees Celsius). Dr. Sniderman adds that normal body temperature can vary slightly from child to child, and a temperature up to 100.4 F (38 C) is still considered normal. 

What affects body temperature in children? 

If your child has a high temperature of over 100. 4 F or 38 C (a fever), it could be a sign of a bacterial or viral infection. A high temperature can also be due to heatstroke, which needs medical attention right away. 

When should you be concerned about a fever?   

“Generally, a temperature over 104 F could signal something serious. Call your child’s pediatrician,” Dr. Sniderman advises. Less than that, and you may be able to break their fever at home.  

Low body temperature (under 95 F or 35 C) can also be a sign of serious infection, especially in infants. Sometimes, a low temperature is due to a problem with the thermometer or not taking the temperature correctly. But if a low temperature at home is accurate, it’s a good idea to contact your pediatrician. 

Normal blood pressure in children 

Several factors can influence a child’s blood pressure. Age, height and weight all cause variations in blood pressure readings. These numbers, given as systolic/diastolic in mm Hg, are general guidelines: 

• 0 to 3 months: 65–85/45–55.  
• 3 to 6 months: 70–90/50–65. 
• 6 to 12 months: 80–100/55–65. 
• 1 to 3 years: 90–105/55–70. 
• 3 to 6 years: 95–110/60–75. 
• 6 to 12 years: 100–120/60–75. 
• 12 to 18 years: 100–120/70–80. 

What affects blood pressure in children? 

Your child’s blood pressure may temporarily be high due to stress, anxiety or exercise. It’s usually not a cause for concern. 

High blood pressure as a medical condition is somewhat common in adults, but it’s rare in children. If your child does have high blood pressure over time — not just a one-time high reading — it could be caused by kidney disease. If your pediatrician is concerned about your child’s blood pressure, a blood test for kidney function is often the next step. 

A blood pressure measurement that’s lower than the normal range is typically nothing to worry about as long as your child isn’t also showing signs of infection or illness. Extreme dehydration can cause low blood pressure. If your child is showing signs of an infection, or dehydration, a serious condition, seek medical attention right away. 

Normal heart rate in children 

The normal heart rate ranges for children by age group, in beats per minute: 

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• 0 to 3 months: 110–160. 
• 3 to 6 months: 100–150. 
• 6 to 12 months: 90–130. 
• 1 to 3 years: 80–125. 
• 3 to 6 years: 70–115. 
• 6 to 12 years: 60–100. 
• 12 to 18 years: 60–100. 

What affects heart rate in children? 

Heart rate in children can be higher than normal for many of the same reasons it can happen in adults, such as: 

• Anxiety. 
• Dehydration. 
• Exercise. 
• Fever. 
• Illness. 
• Stress. 

A very fast heart rate can signal heart rhythm problems. If your child’s heart rate is too fast to count, that’s a sign to seek medical care. 

A low heart rate can be normal for active or athletic children. But it also can indicate a possible heart rhythm issue. If you’re concerned or have questions, talk to your pediatrician.  

Normal respiratory rate in children 

Respiratory rates vary a lot by age, and it’s normal for a baby to breathe much faster than an older child. 

The normal respiratory rates for children by age group, in breaths per minute: 

• 0 to 3 months: 30–60. 
• 3 to 6 months: 30–45. 
• 6 to 12 months: 25–40. 
• 1 to 3 years: 20–30. 
• 3 to 6 years: 20–25. 
• 6 to 12 years: 14–22. 
• 12 to 18 years: 12–18. 

What affects respiratory rate in children? 

Just like heart rate, respiratory rate can go up and down a bit throughout the day, depending on what your child is doing. Temporary changes outside the normal ranges are fine. And just like with adults, it’s also normal for children to breathe more slowly while they’re sleeping. 

High respiration rate in children may be due to factors such as: 

• Anxiety. 
• Asthma. 
• Exercise. 
• Fever. 
• Respiratory infection. 

A low respiratory rate can have potentially serious causes, such as: 

• Accidental ingestion of a drug. 
• Medication side effects. 
• Seizure. 
• “Tiring out” after extended difficulty breathing due to an asthma attack or respiratory infection. 

If you suspect any of these causes, seek care right away.  

“A sick child breathing slowly needs medical help,” states Dr. Sniderman. 

If your child’s respiratory rate is low, but there aren’t any other signs of illness, it’s typically nothing to worry about. 

When to see a healthcare provider 

How do you know when to call the pediatrician? 

• Temperature: If your child’s temperature is over 104 F or 40 C, call your pediatrician.   
• Other vital signs: If your child’s vitals are out of the normal range and your child seems unwell, call your pediatrician.  

It’s good to understand basic vital signs. But rest assured that unless your pediatrician has said otherwise, there’s usually no need to closely monitor your child’s vitals.

How the power supply works in each system unit / Habr

The power supply is removed from the case. The bundle of wires on the left connects to the computer. The large component in the middle of the transformer type is the filter inductor. Clickable, like all the photos in the article

Have you ever wondered what is inside the power supply unit (PSU) of your computer? The task of the PSU is to convert the power from the mains (120 or 240 V AC, AC) into a stable DC power, that is, unidirectional current (DC), which your computer needs. The PSU should be compact and cheap, while efficiently and safely converting current. For these purposes, various methods are used in the manufacture, and the PSUs themselves are much more complicated inside than you think.

In this article, we will break down the ATX standard block and explain how it works ¹ .

Like most PSUs today, ours uses a design known as a “switch-mode power supply” (UPS). Now they are very cheap, but it was not always so. In the 1950s, complex and expensive UPSs were used only in rockets and space satellites with critical size and weight requirements. By the early 1970s, however, new high-voltage transistors and other technological improvements had made UPSs much cheaper, so they were widely used in computers. Today you can buy a phone charger with a UPS inside for a few dollars.

Our ATX format UPS is packaged in a brick-sized metal case with many colored cables coming out of it. Inside the case, we see densely packed components. The design engineers were clearly concerned about the compactness of the device. Many components are covered with heatsinks. They cool power semiconductors. The built-in fan does the same for the entire PSU. On KDPV he is on the right.

Let’s start with a brief overview of how the UPS works, and then describe the components in detail. A kind of “conveyor” in the photo is organized from right to left. On the right, the UPS is receiving AC power. The AC input is converted to high voltage DC by several large filter components. This DC current is switched on and off thousands of times per second to generate pulses that are fed into the transformer. It converts high-voltage pulses into high-current low-voltage ones. These pulses are converted to DC and filtered to provide good, clean power. It is fed to the motherboard, drives and drives through the cables in the photo on the left.

Although the process may seem overly complicated, most consumer electronics from cell phones to televisions are actually powered by a UPS. High-frequency current allows you to make a small, lightweight transformer. In addition, switching power supplies are very efficient. The pulses are tuned to provide only the power needed, rather than converting excess power into waste heat as in a linear PSU.

First, the input AC current is passed through an input filter circuit, which filters out electrical noise, that is, erratic changes in electrical current that degrade the signal.

The filter below consists of inductors (toroidal coils) and capacitors. Square gray capacitors are special Class X components for safe connection to AC lines.

Inlet filter components

The 60 hertz alternating current in the network changes direction 60 times per second (AC), but the computer needs direct current in one direction (DC). The full bridge rectifier in the photo below converts AC to DC. The DC outputs on the rectifier are marked with ? and + , and the alternating current enters through two central contacts that constantly change their polarity. Inside the rectifier are four diodes. The diode allows current to flow in one direction and blocks it in the other direction, so the result is that the alternating current is converted to direct current flowing in the desired direction.

GBU606 is visible on the bridge rectifier. The filter circuit is located to the left of the rectifier. The big black capacitor on the right is one of the voltage doublers. The small yellow capacitor is a special ceramic Y-capacitor that protects against voltage surges

Below are two diagrams of how a bridge rectifier works. In the first diagram, the top AC input has positive polarity. Diodes pass current to the DC output. In the second circuit, the AC inputs have reversed polarity, as happens all the time in AC. However, the configuration of the diodes ensures that the output current remains constant (plus is always on top). Capacitors smooth the output.

The two diagrams show the current flow when the AC input signal fluctuates. Four diodes cause current to flow in the direction of arrow

Modern power supplies accept “universal” input voltages from 85 to 264 volts AC, so they can be used in different countries regardless of the voltage in the local network. However, the circuitry of this old PSU could not handle such a wide range. Therefore, a switch is provided to select 115 or 230 V.

Switch 115/230 V

The switch uses a smart voltage doubler circuit. The idea is that with the switch closed (at 115V), the AC input bypasses the two bottom diodes in the bridge rectifier and instead connects directly to the two capacitors. When “plus” on the top AC input, the top capacitor receives full voltage. And when the “plus” is below, then the bottom. Since the DC output comes from both capacitors, the output is always double the voltage. The fact is that the rest of the PSU receives the same voltage, regardless of whether the input is 115 or 230 V, which simplifies its design. The disadvantage of a doubler is that the user must set the switch to the correct position or risk damaging the PSU, and the PSU itself requires two large capacitors. Therefore, in modern PSUs, the voltage doubler has gone out of fashion.

Voltage doubler circuit. Each capacitor receives full voltage, so the DC output is double the voltage. Gray diodes are not used in the operation of the doubler

For safety reasons, the high and low voltage components are separated mechanically and electrically, see photo below. On the main side are all the circuits that are connected to the AC network. On the secondary side – low-voltage circuits. The two sides are separated by “border isolation”, which is marked with a green dotted line in the photo. Doesn’t cross the border no electrical connections. Transformers pass energy across this boundary via magnetic fields without a direct electrical connection. Feedback signals are transmitted to the main side using opto-isolators, that is, light pulses. This separation is a key factor in a safe design: a direct electrical connection between the AC line and the output of the PSU creates a risk of electric shock.

Power supply with main parts label. Heat sinks, capacitors, control board and output cables removed for better visibility (SB stands for standby supply)

At this point, the AC input has been converted to high voltage DC about 320 V ² . The direct current is cut into pulses by a switching (pulse) transistor ( switching transistor in the diagram above). This is a power MOSFET ³ . Since it heats up during use, it is installed on a large radiator. The pulses are fed into the main transformer, which in a sense is the heart of the PSU.

The transformer consists of several coils of wire wound on a magnetizable core. High-voltage pulses entering the primary winding of the transformer create a magnetic field. The core directs this magnetic field to other, secondary windings, creating a voltage in them. This is how the UPS generates the output current safely: there is no electrical connection between the two sides of the transformer, only the connection through the magnetic field. Another important aspect is that there are many turns of wire around the core in the primary winding, and much less in the secondary circuits. The result is a step-down transformer: the output voltage is much less than the input, but at a much higher voltage.

Switching transistor ³ is controlled by an integrated circuit called “UC3842B Current Mode PWM Controller”. This chip can be considered the brain of the PSU. It generates pulses at a high frequency of 250 kilohertz. The width of each pulse is adjustable to provide the desired output voltage: if the voltage starts to drop, the chip produces wider pulses to pass more power through the ⁴ transformer.

Now you can look at the second, low-voltage part of the PSU. The secondary circuit produces four output voltages: 5, 12, ?12, and 3.3 volts. There is a separate transformer winding for each output voltage and a separate circuit to produce that current. The power diodes (below) convert the outputs of the transformer to DC. Then inductors and capacitors filter the output from voltage spikes. The PSU must regulate the output voltage in order to maintain it at the proper level even when the load increases or decreases. Interestingly, BP uses several different methods of regulation.

Close-up showing output diodes. Cylindrical diodes are vertically mounted on the left. In the center are pairs of rectangular power Schottky diodes, each housing has two diodes. These diodes are attached to a heatsink for cooling. On the right, note the two copper wires in the form of staples. They are used as current sensing resistors

The main outputs are 5V and 12V. They are controlled by a single controller chip on the main side. If the voltage is too low, the IC increases the pulse width, passing more power through the transformer and increasing the voltage on the secondary side of the PSU. And if the voltage is too high, the chip reduces the pulse width. Note: The same feedback circuit drives the 5V and 12V outputs, so a load on one output can change the voltage on the other. In higher quality PSUs, the two outputs are regulated separately ⁵ .

Underside of PCB. Pay attention to the large distance between the circuits of the main and secondary sides of the PSU. Also note how wide the metal tracks on the main side of the PSU are for high current and how thin the tracks are for the control circuits

there is no electrical connection (the photo shows a wide gap). The trick is to use a clever chip called an opto-isolator. Inside the chip, there is an infrared LED on one side of the chip, and a light-sensitive phototransistor on the other. The feedback signal is applied to the LED and detected by the phototransistor on the other side. In this way, the opto-isolator provides a bridge between the secondary and primary sides, transmitting information by light rather than electricity ⁶ .

The power supply also provides a negative output voltage (?12V). This voltage is mostly obsolete, but was used to power serial ports and PCI slots. ?12V power regulation is fundamentally different from +5 and +12V regulation. The ?12V output is controlled by a zener diode (Zener diode) – this is a special type of diode that blocks reverse current to a certain voltage level, and then begins to conduct it. Excess voltage is dissipated as heat through a power resistor (pink) driven by a transistor and a zener diode (because this approach wastes power, modern high efficiency PSUs do not use this method of regulation).

The ?12V supply is regulated by a tiny ZD6 zener diode about 3.6mm long on the underside of the PCB. The corresponding power resistor and transistor A1015 are on the top side of the board.

Perhaps the most interesting regulation circuit is the 3.3 V output, which is controlled by a magnetic amplifier. A magnetic amplifier is an inductor with special magnetic properties that make it work like a key (switch). When current is applied to the inductor of a magnetic amplifier, it initially blocks the current almost completely as the inductor becomes magnetized and the magnetic field increases. When the inductor reaches full magnetization (that is, saturates), its behavior suddenly changes – and the inductor allows particles to flow unhindered. The magnetic amplifier in the PSU receives pulses from the transformer. The inductor blocks the variable part of the pulse. 3.3V output adjustable by changing the pulse width ⁷ .

The magnetic amplifier is a ring of ferrite material with special magnetic properties. Several turns of wire wound around the ring

The power supply has a small board on which the control circuit is placed. This board compares the voltage with a reference to generate feedback signals. It also monitors voltage to generate a “power good” signal. The circuit is installed on a separate perpendicular board, so it does not take up much space in the PSU.

The main components are mounted on the top side of the board with through holes, and the bottom side is covered with tiny SMD components that are applied by surface mounting. Note zero resistance resistors as jumpers

There is also a second circuit in the PSU – for backup power ⁹ . Even when the computer is formally “off”, the five-volt backup power supply provides it with 10 watts of power for functions that continue to work: real time clock, wake-up on LAN, etc. The backup power circuit is almost an independent power supply: it uses a separate control chip, a separate transformer and separate components on the secondary side of the DC, but the same components on the main side of the AC. This system is much less powerful, so there is a smaller transformer in the circuit.

Black/yellow transformers: the backup transformer is on the left and the main transformer is on the right. In front of it is a microcircuit for managing backup power. The large cylindrical capacitor on the right is the voltage doubler component. The white drops are the silicone that isolates the components and holds them in place

An ATX power supply is internally complex, with many components ranging from massive inductors and capacitors to tiny surface mount components ¹⁰ . However, this complexity allows the production of efficient, small and safe PSUs. For comparison, I once wrote about a 1940s power supply that put out only 85 watts of power, but was the size of a suitcase, weighed 50 kg and cost crazy money. Nowadays, with advanced semiconductors, they make much more powerful PSUs for less than $50, and such a device will fit in your hand.

Model 19 TTY Power Supply REC-30 (US Navy) 1940s

I’ve written about PSUs before, including the history of power supplies in IEEE Spectrum. You may also like the detailed dissections of Macbook Charger and iPhone Charger.

¹ Intel introduced the ATX standard for personal computers in 1995. The ATX standard (with some updates) still defines the motherboard, chassis, and power supply configuration of most desktop computers. Here we are looking at a 2005 power supply, and modern PSUs are more advanced and efficient. The basic principles are the same, but there are some changes. For example, instead of magnetic amplifiers, DC / DC converters are used almost everywhere.

PSU label

The PSU label indicates that it was manufactured by Bestec for the Hewlett-Packard Dx5150 desktop computer. This PSU is slightly different from the ATX format, it is more elongated in length. [back]

² You may wonder why 230 V AC is converted to 320 V DC. The reason is that AC voltage is usually measured as RMS, which in a sense averages out the changing waveform. In fact, there are peaks up to 320 volts in a 230 volt AC signal. The PSU capacitors are charged through the diodes to peak voltage, so the DC current is about 320 volts (although it sags a bit during the cycle). [back]

³ The power transistor is a FQA9N90C power MOSFET. It withstands 9 amps and 900 volts. [back]

⁴ The integrated circuit is powered by a separate winding on the transformer, which provides 34 volts for its operation. There is a chicken-and-egg problem: the control chip creates pulses for the transformer, but the transformer powers the control chip. The solution is a custom trigger circuit with a 100 kΩ resistor between the IC and the high voltage current. It provides a small current to start the chip. As soon as the chip starts sending pulses to the transformer, it is powered by it. [back]

⁵ The method of using one control loop for two outputs is called cross regulation. If the load on one output is much higher than the other, the voltages may deviate from their values. Therefore, many PSUs have minimum load requirements on each output. More advanced PSUs use DC/DC converters for all outputs to control voltage accuracy. See these two presentations for more information on cross-regulation. One of the discussed methods is the multi-level laying of the output windings, as in our PSU. Specifically, the 12 volt output is implemented as a 7 volt output on top of the 5 volt output, resulting in 12 volts. With this configuration, a 10% error (for example) in a 12V circuit would be only 0.7V, not 1.2V. [back]

⁶ Opto-isolators are PC817 components that provide 5000 volts of isolation between the sides of the PSU (that is, between the high and low sides). Pay attention to the slot in the PCB under the opto-isolators. This is an additional safety measure: it ensures that high voltage current does not pass between the two sides of the opto-isolator along the PCB surface, for example, in the presence of contamination or condensation (in particular, the notch increases the creepage distance). [back]

⁷ The pulse width is set via the magnetic amplifier by a simple control circuit. In the reverse part of each pulse, the inductor is partially demagnetized. The control circuit regulates the degaussing voltage. Higher voltage increases degaussing. The inductor then takes longer to remagnetize and thus blocks the input pulse longer. With a shorter pulse in the circuit, the output voltage decreases. Conversely, a lower demagnetization voltage results in less demagnetization, so the input pulse is not blocked for as long. As a result, the output voltage is regulated by changing the demagnetization voltage. Please note that the pulse width in the magnetic amplifier is controlled by the control chip. The magnetic amplifier reduces these pulses as needed while adjusting the output voltage to 3.3 V. [back]

⁸ The control board contains several ICs, including the LM358NA op-amp, TPS3510P supervisor/reset chip, LM339N four-channel differential comparator, and AZ431 precision reference. The supervisor chip is interesting – it is specifically designed for the PSU and controls the output voltage so that it is not too high and not too low. The AZ431 precision reference is a variant of the TL431 reference chip that is often used in power supplies to provide a reference (control) voltage. I already wrote about TL431. [back]

⁹ The backup power supply uses a different configuration, a flyback transformer. The A6151 control chip with a switching transistor is installed here, which simplifies the design.

PSU schematic using A6151. It is taken from the reference book, therefore it is not identical to our PSU circuit, although it is close to it
[back]

¹⁰ If you want to study detailed circuits of various ATX format PSUs, I recommend Dan Melnick’s site. It’s amazing how many BP implementations exist: various topologies (half-bridge or direct), the presence or absence of power factor conversion (PFC), a variety of control, regulation and monitoring systems. Our PSU is pretty similar to the straight topology PSU without PFC at the bottom of that page on Dan’s site. [back]

How to choose a power supply – a quick guide – Hardware on DTF

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This article is a small guide and will tell you about choosing a power supply for your personal computer. At the end there will be a kind of tl;dr – those who wish can go directly to it.

Well, let’s get started!

You select PC components for your immediate needs. What components do you start with? I’ll try to guess: from the processor and video card. What’s next? RAM, motherboard and drives? Cooling system, case and monitor?

What about the power supply?

PSU is that PC element that people think about last, sometimes leaving its purchase “for change” and not attaching serious importance to its critical role in any assembly. But in vain. After all, the right choice of PSU can save you from many problems, starting with the unstable operation of the entire system and ending with a fatal component failure.

In this small “guide for dummies” (without going deep into circuitry, serious analysis of power circuits and detailed consideration of standards), we will consider the main characteristics of power supplies and points that you should pay attention to when choosing a PSU.

PSU – the heart of your PC

The power supply is the sole source of power for all components of your PC and is responsible for providing stable and correct power.

The main tasks of the BP are as follows:

1. Current “rectification”.

The mains uses alternating current. The components of your PC, in turn, need a constant. Converting AC to DC and provides power supply.

2. “Delivery” of current of various voltages to the elements of your PC

Different components of your computer require different supply voltages, and some components require several power lines with different voltages at once. The main voltage lines are +3.3V , +5V and +12V . The most powerful consumers (processor, video card and northbridge) use lines +12V and +5V .

Characteristics of power supplies.

Power

The main characteristic of a PSU is its power, measured in watts. The value of the power supply unit for the stable operation of our system must be no less than the value that our system consumes in maximum performance mode. The most “gluttonous” consumers include a video card and a processor. The remaining components consume less electricity.

For an approximate calculation of the PSU power suitable for our system, it is necessary to add up the energy consumption values ​​of all system components and add up to 20% “in reserve”, thereby laying a certain reserve.

It’s easy to find out the amount of power consumption of a processor and a video card: just look at the description of this parameter in their performance characteristics. When overclocked, these components begin to consume significantly more electricity than in stock mode – tests tell about this in detail.

An example of increasing the power consumption of the i7-9700K processor at various stages of overclocking

Also, when calculating the maximum possible consumption of a video card, you can focus on the number of connectors and their allowable power transfer limits: PCI-E 16x – 75 W, 6 -pin – 75 W, 6 + 2 -pin – 150 W. Thus, the theoretical power consumption limit of a video card with two 6-pin and 6+2-pin connectors is limited to 300 watts.

The power consumption of the motherboard depends on the following factors: the number of power phases, the type of voltage regulator, the chipset and additional modules (integrated sound chip, Wi-Fi module, the number of ports and connectors and their type). As a rule, motherboards consume around 40-50 watts, but the power consumption of some top models can reach 80 watts or more under heavy load.

The optical drives should also be considered in the calculation: their power consumption can be up to 30 W for some models of SATA DVD and Blu-Ray drives.

Data drives are generally not major energy consumers. When calculating the approximate power consumed by the system, the amount of electricity consumed can be taken as: 8-10 W for each hard drive, and 3 W for each SSD.

Elements of the cooling system (both the processor and additional case fans) are often not considered as serious consumers of electricity – and in vain. 120mm and 140mm fans, when operating at 2000 rpm, can consume up to 6-7 watts each, depending on the model. Therefore, they definitely need to be considered, especially if there are several such turntables inside the case. Up to 20 watts can be put on the processor cooling system itself, whether it’s a tower cooler or an AIO dropsy.

The RAM is one of the most economical consumers in the system, so 5 watts per stick should be more than enough. The power consumption of RAM is weakly correlated with its volume, that is, an 8 GB bar will consume almost as much as a 4 GB bar, all other things being equal.

To facilitate the calculation of the total power consumption of , you can use specialized programs or online calculators on the websites of PSU manufacturers. From myself, I recommend this one as an easy-to-use and visual version of the power calculator.

efficiency

High power does not guarantee the quality of the PSU and its efficiency. The efficiency of the power supply is evidenced by its efficiency.

Power supply efficiency shows how much power from the network goes to your system. The higher the efficiency value, the less the power supply heats up, consuming electricity more efficiently. Due to less heating, both a better temperature regime and a quieter operation of the cooling system are ensured.

PSU efficiency rated to 80 PLUS. This standard implies several levels of performance, in ascending order:

• 80 PLUS White/Standard
• 80 PLUS Bronze
• 80 PLUS Silver
• 80PLUS Gold
• 80PLUS Platinum
• 80 Plus Titanium

As you can see from the table, the main difference between the various levels of certification of the 80 PLUS standard is the efficiency of the power supply at loads of 20%, 50% and 100%. The higher the level to which the PSU corresponds, the higher its efficiency and, accordingly, the price.

Poorly designed power supplies generally fail certification, so 80 PLUS compliance is an added guarantee of quality. You can check the actual compliance of the PSU with the 80 PLUS standard on the Plug Load Solutions website.

Current on individual lines

The total power of the power supply is the sum of the powers it can provide on the individual power lines. If the load limit on one of the lines is exceeded, the system may lose stability, even if the total power consumption is far from the nominal. As mentioned above, the main lines of force are +3.3V , +5V and +12V :

• +12 volts are supplied primarily to the video card and processor. On this line, the power supply must provide as much power as possible
• +5 volts supplied to motherboard, drives and optical drives
• +3.3 volts are supplied to the motherboard and RAM.

Information on the power lines and the current transmitted through them is available on the technical data sheet of the PSU as a sticker (the application of information and its appearance may differ depending on the PSU model / manufacturer). Most often it is expressed as a description of the maximum load.

An example of a sticker with performance characteristics – designations of current and power on power lines

Power factor correction

The Power Factor Correction (PFC) module allows you to increase the efficiency of the power supply. It is a special element designed for power factor correction and aimed at protecting the network.

PFC modules are divided into active and passive. An active power factor correction (APFC) module equalizes the input voltage, allowing stable operation of all devices that output an analog signal from the computer. PSU models with APFC are more expensive than models with a passive version of this module.

Dimensions and form factor. Weight.

Consider the most common modern standard for the PSU mass segment – ATX.

The ATX standard guarantees dimensional compatibility with standard ATX cases and electrical specifications for ATX motherboards.

In most cases, the only electrical specification that matters to us will be ATX12V 2.x.

A standard ATX power supply has dimensions of 150mm * 86mm in width and height, while the length (aka depth) varies depending on the model.

If you decide to build a compact system and the space for the power supply is limited by the small size of the case, you should take a closer look at the SFX and SFX-L form factor devices.

Comparison of ATX, SFX-L and SFX PSU dimensions (from largest to smallest) Source: smallformfactor.net

They are more compact in size while meeting the ATX12V 2.X standard in terms of electrical performance.

The weight of a power supply usually indicates the quality of the components used. The heavier the power supply, the better. Weight is not an absolute indicator when choosing, however, a suspiciously light PSU should immediately lead you to the idea that the product is not of the highest quality.

Cable management

With regard to the method of fixing cables, power supplies can be divided into three main groups:

• Non-modular PSU
• PSU of semi-modular design (semi-modular)
• PSU fully modular

The main difference between the types of construction is the ability to disconnect the complete wires and install only the ones you need in the quantity that your system components need. Let’s look at them in a little more detail:

1. Non-modular

The main feature is that all bundled cables for all connectors are connected to the PSU without the possibility of disconnecting them.

As such, this design has no pluses, but “macaroni” can be written down as minuses – it can be difficult to achieve a neat management of all cables. If you don’t need some complete cables due to the small number of components in your system, then remove them you can’t – they will remain inside the case of the system unit.

2. Semi-modular

Only the main cables come with no detachable option: 24-pin ATX, PCIE, 8-pin cable for the CPU and one or two SATA/MOLEX cables for peripherals.

The main plus is easier cable management and efficient organization of space inside the system unit.

3. Full Modular

Full modular design allows you to disconnect any cables from the PSU, thus adjusting everything for yourself.

Of the benefits – the easiest of all three types of cable management and the most efficient organization of space inside the system unit.

An important consideration when considering cable management options is cable sheathing. It allows you to avoid clamps and fractures when organizing space inside the system unit, and also greatly simplifies installation.

Cooling.

Depending on its characteristics, size and form factor, the power supply can be equipped with a fan size from 40mm to 140mm.

Many modern models allow you to adjust the fan speed, thereby achieving a reduction in noise level. But do not forget about the cooling efficiency of a PSU with not the highest efficiency.

Upgrading stock cooling to higher quality is a common option among enthusiasts. Installing a better fan can, in some cases, significantly improve temperature performance.

Some models are equipped with a so-called “hybrid cooling system”. This term is used to automatically turn off the fan when the load on the PSU is low (for example, when the system is idle). This allows, to a certain extent, to reduce the noise emission of your assembly, but is not a mandatory element of the power supply.

Manufacturer’s warranty.

Typical power supply warranty options are 2 years, 3 years, 5 years, 7 years, and 10 years. It would be logical to assume that the longer – the better for the consumer. A long warranty period also indirectly indicates the quality of the PSU – the manufacturer is confident in a lower probability of component failure over time.

Manufacturer

Again, everything is quite simple – a well-known brand and the presence of good reviews on the trading floors allow you to make the right choice. Personally, I would recommend a PSU from Corsair, EVGA, Seasonic, Chieftec, Silverstone. But that doesn’t mean that Thermaltake, Enermax, Cooler Master, NZXT, and others make bad PSUs.

It is also worth noting that behind all the variety of manufacturers of power supplies and their lines on the market, there are basically the same OEMs. Most well-known companies do not have their own production, and you can find out the real manufacturer by markings on the boards inside the power supply.

Certification

FCC, CE, UL, TUL approval and certification is an important consideration when choosing a device. And if FCC and CE certification is de facto mandatory for most consumer devices, then passing additional third-party certifications is at the discretion of the manufacturer, and is a sign of the quality of the device.

In addition to being mandatory, most PSUs are also certified by Underwriters Laboratories and TÜV.

The American company Underwriters Laboratories is engaged in standardization and certification.

UL listed power supplies are marked with their logo and serial number. By this serial number, starting with the letter E, you can determine the manufacturer and view the PSU parameters. To do this, simply enter this serial number in the online UL database.

As a result, you will receive information about the real PSU manufacturer, as well as a link to a document that contains the main characteristics of the device, including the maximum load on the lines.

Example of designation of different types of certification

TÜV is a German organization responsible for product safety control. It includes three holdings: TÜV SÜD, TÜV Rheinland and TÜV Nord.

Similar to UL certification, TÜV-certified power supplies have the company logo and certificate serial number imprinted on their body. Also, similar to UL certification, this serial number can be entered on the TÜV website and get detailed information about the device.

Please note that the full information on UL and TÜV certification may not be applied to the label on the power supply itself, but located on the box. In extreme cases, you can contact the manufacturer’s support service to clarify the availability of a specific type of certification.

TL;DR

To summarize. How to choose a power supply?

So, the following points must be considered:

• Sufficient power. Choosing a PSU with 15-20% headroom will avoid system stability issues and provide headroom for overclocking components and possible upgrades in the future
• High efficiency. Consider buying an 80 Plus certification PSU, the more efficient the better
• Sufficient power on +12V lines for main consumers (video card and processor)
• Presence of PFC module
• ATX12V 2.X Compliant
• Cable connection diagram. A fully modular design is the preferred allows you to assemble the system with greater ease and more efficiently organize the space inside the system unit
• Proven and well-known manufacturer providing a long-term power supply warranty (minimum 5 years, preferably all 10)
• Certification FCC, CE, UL, TÜV
• Power supply weight.