The switching power supply does NOT hold the load
The reason for the failure of the power supply, or why the technique stops working. Recently, I began to notice more and more that people began to apply, and I myself find myself in a strange and monotonous repair of equipment. It all starts in approximately one scenario. the device worked for an hour or two and then suddenly it started to turn on slowly, or NOT to start at all, or when turned on, it turns off abruptly, or it tries to turn on but does not turn on! In general, we take a tester and check the power supply by measuring the voltage on it, more precisely at the output terminals, it is usually within acceptable limits, or, as an option, it differs by 0.3-0.4 volts downward, for example, in 12 volt power supplies, it is usually 11.4 volts.
But if you check with an oscilloscope, or a simple tester from a speaker, you can hear high-frequency ripples, so without smoothing this equipment with such a power supply cannot work!
Such capacitors, as a rule, externally noticeably swell on the lid or explode altogether, when checked, they may show a noticeable decrease in capacitance. instead of 1000 μF, there will be 120-150 μF, or even less, or in the tester the capacitor can be defined as another element.
With such a miracle, when the capacitor suddenly becomes a resistor or diodes, the power supply tries to turn on, but the currents become high and in large branded TVs such blocks go into protection. With a new attempt to turn on everything is repeated in a circle.
Often, replacing the filter capacitor can be done with an increased capacity, for example, instead of a battery of three capacitors of a rare capacity of 1500 uF, you can put it in 4000 uF. The main thing is to check then the stability of the device and the level of ripple, so that everything is normal, well, so that the capacitor is at the required voltage, or better with a voltage margin, then it will be additionally protected from surges.
In this article, I will talk a little about the basics of repairing computer, switching power supplies of the ATX standard. This is one of my first articles, I wrote it about 5 years ago, for this I ask you not to judge strictly.
Repairing impulse power supplies is a rather dangerous activity, especially if the malfunction concerns the hot part of the power supply. Therefore, we do everything thoughtfully and carefully, without haste, in compliance with safety measures.
Power capacitors can hold a charge for a long time, so do not touch them with bare hands immediately after turning off the power. Under no circumstances should you touch the board or the heat sink when connecting the power supply to the network.
In order to avoid fireworks and keep the elements still alive, you should solder a 100 cotton bulb instead of a fuse. If the lamp flashes and goes out when the power supply is turned on, everything is fine, and if the lamp lights up and does NOT go out when turned on, there is a short circuit somewhere.
Check the power supply after repairs have been carried out away from flammable materials.
Soldering iron, solder, flux. We recommend a soldering station with power regulation or a pair of soldering irons of different capacities. A powerful soldering iron is needed to solder transistors and diode assemblies, which are located on radiators, as well as transformers and chokes. A lower power soldering iron solders various small things.
Solder suction and / or braid. Serve to remove solder.
Side cutters. Used to remove plastic clamps that tighten the wires.
100 watt light bulb
Refined gasoline or alcohol. Used to clean the board from traces of soldering.
Power supply device.
A little about what we will see by opening the power supply.
Internal view of an ATX power supply
A. diode bridge, used to convert AC to DC
B. power capacitors, used to smooth the input voltage
Between B and C. the radiator on which the power switches are located
C. pulse transformer, serves to form the required voltage ratings, as well as for galvanic isolation
Between C and D. a radiator on which the rectifier diodes of output voltages are located
D. group stabilization choke (DGS), serves to smooth out noise at the output
E. output, filter, capacitors, serve to smooth out noise at the output
24 pin connector pinout and voltage measurement.
We will need knowledge of the contacts on the ATX connector to diagnose the power supply. Before proceeding with the repair, you should check the voltage of the standby power supply, in the figure this contact is marked in blue 5V SB, usually it is a purple wire. If the attendant is in order, then you should check the presence of the POWER GOOD (5V) signal, in the figure this contact is marked in gray, PW-OK. Power good appears only after turning on the power supply. To start the power supply by shorting the green and black wires, as in the picture. If PG is present, then most likely the power supply has already started and the remaining voltages should be checked. Please note that the output voltages will differ depending on the load. So, if you see 13 volts on the yellow wire, do not worry, it is likely that under load they stabilize to the standard 12 volts.
If you have a problem in the hot part and you want to measure voltages there, then all measurements must be made from a common ground, this is minus the diode bridge or power capacitors.
The first thing to do is to open the power supply and make a visual inspection.
If the PSU is dusty, clean it. We check if the fan is spinning, if it is standing, then this is most likely a prerequisite for the failure of the power supply unit. In this case, you should look at the diode assemblies and VTS. They are most prone to failure due to overheating.
Next, we examine the power supply unit for burnt-out elements, darkened by the temperature of the PCB, swollen capacitors, charred insulation of DHS, broken tracks and wires.
Before opening the power supply unit, you can try to turn on the power supply unit in order to determine the diagnosis for sure. Correctly Diagnosed. Half of the Treatment.
The power supply unit does not start, there is no standby power supply voltage
The power supply unit does not start, but the standby voltage is present. Sun signal PG.
BP goes to defense,
BP works but stinks.
Output voltages are overestimated or underestimated
Checking with a multimeter
If the method did NOT give anything and the alternating current is supplied to the power supply unit, it is worth finding out if it correctly converts the alternating current into the direct current required by the internal parts of the PC. This requires a multimeter.
For this you need:
Connect something to the PSU: floppy drive, HDD, coolers, etc.
Connect the negative test lead of the multimeter to the black contact of the pin connector. This will be ground.
The positive terminal should be connected to the contacts with colored wires and compare the values with the reference values.
The main symptoms and malfunctions
The power supply rarely fails. The most often broken are low-quality PSUs, which usually produce brand names. Unstable voltage in the power grid is another cause of breakdown. In this case, the entire device may even “burn out”.
In addition, one of the most important reasons for the unstable operation of the power supply unit is the incorrectly calculated power. Each component of the computer needs power, and if the required minimum is NOT met, problems can not be avoided: the new device will NOT withstand the load.
In fact, there are concrete signs that the unit has lost its efficiency. But there are indirect symptoms:
- DOES NOT respond to switching on: the coolers remain motionless, the lights are off, there is sound.
- PC does not always start the first time.
- The computer shuts down itself at the stage of loading the OS, slows down.
- Memory error.
- Winchester stopped working.
- Unfamiliar noise during PC operation.
Before drawing conclusions and delving into the technical jungle, the first step is to check everything visually.
What is needed for this:
Completely de-energize the system, wear an electrostatic bracelet or gloves for safety.
Open the case.
Disconnect all components from the PSU: storage, oregano, video adapter, etc.
Tip: before disconnecting the components, it is best to take a photo, so that later quickly and easily assemble the computer back.
Armed with a screwdriver, detach the unit and disassemble it.
You need to see if the device is dusty, and if its capacitors are swollen. Also pay attention to the fan stroke. He must be free. If everything, at first glance, is in order. go to the next item.
In addition to hardware solutions, there is a lot of software with which you can test the condition of components, perform diagnostics and get the necessary information about the device. One of these utilities is OCCT Perestroika, which is available on the official website for free.
- Accurate diagnosis.
- Simple and intuitive interface.
- Easy installation.
- Works with both 32- and 64-bit OS.
How to check a power supply for a computer: correctly checking a power supply in 4 ways
If something is wrong with the power supply unit, other elements of the computer filling are not able to work correctly. Periodic check of the unit will help identify the problem at an early stage and quickly deal with it.
How to check your computer’s power supply: options
There are four diagnostic methods that work. They are described below.
The so-called paper clip method is a simple and effective diagnostic method. Naturally, before performing this procedure, it is also necessary to de-energize the PC, while the PSU must be disconnected Not only from the outlet, but also using the off / on button located on the device itself, and disconnect all components from it.
- Take a paper clip, it will play the role of a jumper, bent it in an arc.
- Find the 20-24 pin connector coming from the PSU. It is not difficult to recognize it: it takes 20 or 24 colored wires. It is he who serves to connect to the motherboard.
- Find the two marked with numbers 15 and 16. Or it can be black and green wires, which are next to each other. How correctly the first. several, and the second. one. They indicate the connection to the motherboard.
- Insert a paperclip firmly into these pins to simulate the process of connecting to the motherboard.
- Release the jumper from your hands, as current can pass through it.
- Reapply power to the power supply unit: if its cooler starts up, everything is in order.
Tips for using the power supply
The stability of the system depends on which power supply unit is in the computer. It is certainly not worth saving on this component, and even more so you should not trust noun-name firms. The fact is that in this case, the declared characteristics, most likely, will NOT coincide with the real ones.
As mentioned above, when choosing a power supply, it is necessary to correctly calculate its power. There are quite handy online calculators for this.
Interesting: CTG-750C-RGB has backlighting, and extra wires can be disconnected from it.
Do NOT overload the PSU too much. For example, even if the user has chosen a suitable option in terms of power, the block may NOT pull new components after the upgrade. In order not to buy another power supply unit, it is better to choose a device with a margin of 20-30%.
When using the power supply, it is important to remember about possible voltage surges, short circuits and other problems in the electrical network, which may occur unexpectedly. Better pay attention to the protected options: they last longer. For example, PS-SPR-0850FPCBEU-R overloads, voltage drops are terrible. He is also not afraid of short circuit.
It is not difficult to carry out a physical examination of a computer PSU. However, this requires skill, because you will have to disassemble the PC case, as well as the component itself.
Computer literacy with Hope. Filling in the Gaps. Expanding the Horizons! 7 rules for using laptop batteries
The block cannot last forever,
but you can extend the period of its flawless work.
The block is not forever. Eternal laptop batteries are NOT invented yet. But the battery life can be extended. How? Observing the following 7 rules for using the laptop battery.
Rule 1. When you turn on the laptop for the first time after buying it Wait until the unit is charged to 100%. DO NOT unplug your laptop and charger until this happens. Even if the laptop battery takes a long time to gain its charge.
At the same time, when you turn on the laptop for the first time after purchasing it, adjust the power settings to continue using the laptop battery. How to do it? In Windows 7: left-click on the battery icon located in the taskbar on the right side (more precisely, in the notification area), and select the “Advanced power options” option. You can also “get” there from the Control Panel “Start”. “Control Panel”. “Hardware and Sound”. “Power Supply“.
The recommended power settings have been listed in the “Automatically manage laptop power supply” article. However, these are only recommended parameters, since each user can and should adjust these parameters “for themselves” and for their laptop and for their own operating modes of the laptop battery.
Rule 2. When using the laptop for the first time (immediately after turning it on for the first time after purchase), it is recommended to fully discharge the battery three times and then immediately (without leaving the battery completely discharged for a long time!).
During a three-fold full discharge and battery charge, it is not recommended to load the laptop to the maximum (in terms of power consumption), for example, watching movies from DVD. Allow the battery to run at partial load for the first time. By doing so, you will extend the battery life of your laptop in the future. It’s like driving a car, until you drive it in, you don’t need to drive at maximum speed.
Subsequently, repeat this cycle of full discharge and FULL charge of the battery three times approximately once a year. The phrase “FULL charge” means. up to 100%! Disable the maximum battery limit during this “workout”. see the following rule.
Rule 3: Limit the maximum battery level if the laptop management software allows you to adjust the maximum battery level. If there are such adjustments, they should be used immediately after completing a three-fold cycle of full battery discharge and subsequent full battery charge.
It is believed that limiting the maximum battery charge of a laptop to 80% or 50% will result in much longer battery life than if the maximum battery charge is at the usual 100%. At the same time, 80% should be installed by those laptop users who more often use a laptop from a battery outside the house and away from a 220V electrical network. And 50% should be installed by laptop users who use it mainly from a 220V network.
How to make these settings? Check your notebook documentation, and if it contains recommendations for battery management, refer to them as soon as you complete the three discharge-to-charge cycle. When you set the maximum battery level to 80% or 50%, all subsequent rules are not overridden!
Rule 4. When using a laptop battery in the future, never leave the battery completely discharged for a long time. At the first opportunity, you need to immediately put it on charge if the battery is discharged to the minimum critical values (0%. 10%).
Rule 5. When using a laptop in the future, never leave the laptop turned off and at the same time connected to a charger, which in turn is connected to a 220V electrical network.
You can leave the laptop connected to the charger if at the time the laptop is turned off, its unit is not fully charged and needs to be charged to 100%. In this case, the laptop should remain connected to the charger only until the battery is fully charged. Then the laptop should be disconnected from the charger or the charger should be disconnected from the 220V network.
Rule 6. When using the laptop battery in the future, use the charger wherever there is access to the 220V network. This will reduce the number of discharge cycles. battery charges.
The duration of the correct operation of the laptop battery depends directly on the number of discharge cycles. charge, which this battery “lived”. The more THESE cycles are performed, the less the battery “lives”.
Rule 7. When using a laptop, exclude situations of uncontrolled discharge of the battery, up to a complete discharge.
What does this mean? For example, leaving a laptop for an indefinite time in the so-called standby mode (a mode when the laptop is turned off, but its state is recorded in the laptop’s RAM for quick recovery when it is turned on again), the user risks forgetting about it for a long time. And the standby mode, albeit a little, but consumes electricity.
If you do not think about the laptop for a long time, then in standby mode you can completely discharge the battery. This means that it can fail with a high degree of probability.
You can also inadvertently forget for a long time about turning on and running on battery laptop. This will also cause a complete discharge of the battery, and rather quickly, in contrast to the economical standby mode, in a matter of hours.
For those who DO NOT rely on their memory, and who understands that they can forget about the included laptop for a long time, we can only advise you to set a high level of low battery power and almost complete battery discharge. For example, instead of the usual 10% and 5%, you can set 50% and 45%. Of course, this will halve the battery life of the laptop, but it will not completely drain the battery.
Summarizing all the rules for using a laptop battery, you can summarize how to extend battery life.
And similarly, it is necessary to prevent a long stay of the battery in a state of full charge (100%) when the laptop is off and at the same time when the laptop is connected to a 220-powered charger.
These are, in fact, all the rules for operating a laptop battery. They sound simple, it is not always possible to fulfill them, but you need to strive to fulfill them. And then the battery pack will not fail, and serve exactly as long as its developers and manufacturers have put in it. And they have already tried, and do not hesitate!
DIY electronic load for the power supply
During testing of the next home-made or repaired power supply, in order to create a load, you have to connect various light bulbs, powerful resistors and pieces of a spiral from an electric stove. Selecting the right load in this way is very time consuming. In order not to waste your precious time and nerves. It’s easier to assemble a simple electronic load with your own hands.
In fact, this is a simple device consisting of powerful transistors that allow you to smoothly load the power supply with a stable regulated current.
This figure shows a diagram of an electronic load on powerful transistors that can load any power supply up to 40A.
Electronic load circuit for power supply
How does this scheme work? The voltage from the tested power supply is supplied to the base of transistor T1 through a voltage divider assembled on resistors R1, P1 and P2 and limiting resistor R2. Transistor T1 controls four powerful transistors T2, T3, T4 and T5 that act as switches and create a controlled load on the power supply. For a more accurate and coarse setting of the load current, the circuit has two variable resistors P1 and P2. The load current and voltage are measured by a Chinese electronic voltmeter ammeter. It is also possible to install pointer devices in place of the electronic.
This circuit is designed for input voltage up to 50V and current strength up to 40A. If you want to increase the amperage, add the required number of TIP36C transistors and 0.15 Ohm 5 W shunt resistors to the circuit. Each added transistor increases the amperage by 10A.
In the process of operation, transistors T2, T3, T4 and T5 get very hot, therefore good cooling is required. Install each transistor on a large radiator with a size of 100x63x33 mm without insulating spacers after that the collectors of the transistors in the diagram are still connected together.
The radiators are cooled by two powerful 120×120 mm fans. Which are powered from a separate power supply through the L7812CV voltage regulator, and a Chinese voltmeter ammeter is also powered from here. Transistor T1 and voltage regulator L7812CV are installed on a separate small heat sink from the computer power supply, so as not to interfere with the power transistors.
With this simple and reliable device, it is easy to load and test any transformer and switching power supplies, as well as batteries and other power supplies.
I hope the electronic load for the power supply will be a useful homemade product for your home radio workshop.
Radio parts for assembly
- Transistor T1 TIP41, MJE13009, KT819
- Transistors T2, T3, T4, T5 TIP36C
- Voltage stabilizer L7812CV
- Capacitor C1 1000 uF 35V
- Diodes 1N4007
- Resistors R1, R2 1K, R3 2.2K, R4, R5, R6, R7 0.15 Ohm 5 W, P1 10K, P2 1K
- Radiators 4 pcs. Size 100x63x33 mm
- Fans 2 pcs. From computer 12V size 120×120 mm
- Chinese voltmeter ammeter for 50A with a shunt, you can put a dial gauge, it will be much more accurate and reliable
Friends, I wish you good luck and good mood! See you in new articles!
80 comments on “DIY electronic load for the power supply
In the characteristics of the device, they say 50V 40A, were they NOT mistaken anywhere? 2kw of power, this handcraft clearly will not stand.
There is one thing here, the higher the voltage, the less current the transistor can withstand. I checked up to 40A at a voltage of 12V. Usually batteries are tested with such a device. So 50V is indicated, which means that you can connect to a 50V power source, only the maximum load current that is safe for transistors will not be more than 1-3A. For example, a fully charged battery from a scooter produces 42V. Connect to an electronic load, I set the discharge current to 1A and determine the battery capacity.
Sergey, hello, I am a beginner radio amateur, I am 27 years old and thank God at my age I found myself a hobby, but unfortunately, I really lack the theoretical part, at the moment I have an idea to collect a load for a computer power supply, but unfortunately for me Lack of experience. Tell me, is it possible to talk to you, so to speak, to hire you part-time as my teacher? I am ready to discuss with you the financial part of this proposal.
Hello, can you tell me if this circuit can be used to discharge various batteries (lithium ion, lithium polymer, etc.)?
Good evening, Yuri! You can discharge any batteries, in fact the device is made for this, the main thing is not to exceed the discharge current permissible for the battery and Monitor the battery voltage, especially if the battery is without a BMS protection board.
Sergey, tell me on the connection terminals of the tested power supply unit should there be a short circuit? Or should there be some kind of resistance? And then I collected everything like yours, but they are also short-circuited, the power supply goes into protection, and the batteries are instantly heated from short-circuit. Ammeter shows 15A.
Comments, KZ are not required. Although it can be done easily by turning the knob of the variable resistor. Try to twist the knobs of both variable resistors all the way in different directions or put them in the middle to find out in which direction the increase occurs and in which direction the load decreases. Wires to variable resistors can be soldered in different ways. When you turn the knob of a variable resistor, transistors T2-T5 open and close, thereby creating resistance. It’s like connecting different resistances to a power source. Transistors serve as a kind of powerful controlled variable resistors to load the power supply. Check how the voltage on the collector of the T1 transistor changes when the knobs of the variable resistors are rotated. If the transistor T1 is NOT serviceable then there will always be a short circuit at the load input.
When heated, the current will NOT float?
Sun with current everything will be fine.
Good evening, Sergei! The shunt from the volt ammeter should be cut out and a 50 A shunt should be connected in its place or what? Regards, Ivan
Good evening, Ivan! The shunt does not need to be cut. If the ammeter is designed for 10A, then the shunt should also be at 10A, when the shunt is installed at 50A, the readings of the device will not be correct.
Thank you. Must buy.
Good evening Sergey! I collected everything according to your scheme, but when turned on, the TIP36 transistors fly out, there was no way of changing the switch for 1k, put it on 120 Ohm, maybe because of it?
Good evening, Ivan! Comments, a variable on 1K, you can not put at all without it, it will work. Something wrongly assembled or transistors from China. I was sent a batch of transistors all Pogorely. The Chinese are doing a disadvantage. Ten Chinese transistors are equal in power to one original. Now only in Chip and Deep I buy normal parts there and sell.
Ivan, it’s all about the initially crookedly constructed scheme. Here is an explanation of the reasons why It will not work normally and some refinement (as far as possible for such a simple scheme):
forum.Cxem.Net/index.php?/topic/180026-%D1%8D%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0% BD% D0% B0% D1% 8F-% D0% BD% D0% B0% D0% B3% D1% 80% D1% 83% D0% B7% D0% BA% D0% B0 / # comments
Dear author, I repeated your design. except for the power supply for coolers and a voltmeter, I used a 12V / 1A power adapter, but I don’t think it’s important. I checked it on linear stabilizers L7812 from the second device. no difference.
As a load for a power supply unit, it works. there are questions here. But I can’t figure out what current the ammeter of your device indicates. The thing is that your tester does not show more than one ampere with kopecks. under any tests: all real indicators can be seen only on the indicators of the tested power supply unit. And if you have to test, say, a power supply unit for an LED strip (as in your photo)? As luck would have it, I didn’t have anything like that at hand.
In a word, the ratio between the Amperage indicators on the tester and on the tested power supply units remained unclear: how to evaluate it. For example, this Chinese PSU:
clearly demonstrates its maximum parameters under load with your tester. 24V / 6A, but it is the VA indicator installed in the same place as this Chinese power supply unit, that is, in a homemade Laboratory power supply unit (the indicator, by the way, is exactly the same as on your tester). And the tester itself at this time. less than 1 A. In short, it remained unclear: what current is the tester showing. The only thing that is more or less consistent is the tension. Naturally, there is a dependence of the current growth on voltage, but everything is within the same specified limits. I also checked the same adapter, which I asked for the design: the voltage of 12V corresponds, but does not even close to the nominal 1A: a maximum of 200mA. I checked the power supply unit where the L7812 stands: it swings at 400mA, although this linear regulator has a maximum of 1.5A. The key did not measure heating, but to the touch it somewhere corresponds to the current.
I checked this BP with your tester:
It can be “shaken” by the tester to the limit values. But again: at 30V / 10 A on the tester indicator. up to 1.12 A. Probably, I have not figured out something. help :).
It’s all about Chinese electronic voltmeters. If you connect a power supply unit with a built-in Chinese voltmeter to an electronic load, then the readings of the two devices on the power supply unit and on the power supply unit will differ twice. The only way out of this situation is to install analog dial gauges on an electronic load or turn off the voltmeter in the tested power supply during the test.
I ordered a switchman from the Chinese for 10A: I’ll see what happens. But there is an idea that the reason is in the shunt: they are usually calculated in the range from 1:99 (say, for a milliammeter) to 5-6 times. as in our case. In addition, the Chinese digicam has its own 10A shunt, so the lion’s share of the current simply flows past the indicator. after all, exactly the same indicators show quite reliable figures on the tested power supplies. Apparently, this requires some other calculation of the shunt, taking into account the “spreading” along the parallel circuits. And so the load is very comfortable. In the end, no one forbids the sequential inclusion of an ammeter in a multimeter: I did just that, having received quite real current figures. True, multimeters that allow you to measure more than 20A, I did not come across.
In the course of the design, the idea came to use the device’s cooling system for Chinese 4Ω / 100W resistors, usually used to test ULF. They are NOT electrically connected to the main circuit. just added to heatsinks and coolers. I put 4 pieces, which makes it possible to combine the load with jumpers on the terminals: for example, two channels of 8 Ohm / 50 W or 2 Ohm / 200 W. I recommend making your life easier :). These are resistors of this kind: aliexpress.ru/item/33026780964.html?Spm=a2g0s.9042322.214.171.1244d33edl5qqu1
Hello. What section guide should you go from transistors to the terminals for checking the power supply? That is, what current flows in the collector circuit of transistors T2-T5? If you use all 40 amperes, then the question becomes relevant. And it is desirable to indicate the power of the resistor R3. thanks.
Good evening! The cross-section of the wire from the bundle of transistors to the PSU should be 4 mm / sq. The current will flow at 10A per transistor. A 0.25 W resistor R3 will suffice.
Hello Sergey! I’m about reworking your circuit ?! Somehow the MJ11032_11033 transistors came to me! Complementary pair! Ideal for electronic loading. True, they are on the Darlington scheme! But on the Internet I have come across an electronic load scheme for Darlington! In my opinion, they were collected on KT827, or KT825!? So here’s a question for you as a Doku, is it possible to apply from in an electronic load. Still according to the Datasheet, it has a power dissipation of up to 300 W.