Switch power supply Let's talk about repairing a computer power supply with your own hands. Power supply device, step-down converter of mains voltage

A typical ATX power supply circuit is shown in the figure. Structurally, it is a classic pulse unit on a TL494 PWM controller, triggered by a PS-ON (Power Switch On) signal from the motherboard. The rest of the time, until the PS-ON pin is pulled up to ground, only the Standby Supply is active with +5 V at the output.

Consider the structure of the ATX power supply in more detail. Its first element is
:

Its task is to convert alternating current from the mains to direct current to power the PWM controller and the standby power supply. Structurally, it consists of the following elements:

• Fuse F1 protects the wiring and the power supply itself from overload in the event of a PSU failure, leading to a sharp increase in current consumption and, as a result, to a critical increase in temperature that can lead to a fire.
• A protective thermistor is installed in the "neutral" circuit, which reduces the current surge when the PSU is connected to the network.
• Next, a noise filter is installed, consisting of several chokes ( L1, L2), capacitors ( C1, C2, C3, C4) and a choke with counter winding Tr1. The need for such a filter is due to the significant level of interference that the pulse unit transmits to the power supply network - this interference is not only picked up by television and radio receivers, but in some cases can lead to malfunctioning of sensitive equipment.
• A diode bridge is installed behind the filter, which converts alternating current into a pulsating direct current. The ripples are smoothed out by a capacitive-inductive filter.

Standby power supply- This is a low-power independent pulse converter based on the T11 transistor, which generates pulses, through an isolation transformer and a half-wave rectifier on the D24 diode, feeding a low-power integrated voltage regulator on the 7805 chip. Although this circuit is, as they say, time-tested, its significant drawback is high voltage drop across the 7805 stabilizer, leading to overheating under heavy load. For this reason, damage in circuits powered from a standby source can lead to its failure and subsequent inability to turn on the computer.

The basis of the pulse converter is PWM controller. This abbreviation has already been mentioned several times, but not deciphered. PWM is pulse-width modulation, that is, changing the duration of voltage pulses at their constant amplitude and frequency. The task of the PWM block, based on a specialized TL494 microcircuit or its functional analogues, is to convert a constant voltage into pulses of the appropriate frequency, which, after an isolation transformer, are smoothed out by output filters. Voltage stabilization at the output of the pulse converter is carried out by adjusting the duration of the pulses generated by the PWM controller.

The problem of choosing a case equipped with a modern high-quality power supply, which, in turn, has decent electrical and ergonomic parameters, is quite relevant. Often cases are equipped with power supplies based on the principle of minimum sufficiency - "it works well." However, given the fact that the complete set of the case with a power supply for the buyer and user is not at all free, and the requirements for testing such power supplies should be appropriate.

Case testing will consist of two parts: testing the case itself and testing the complete power supply, the latter being tested according to a standard methodology, the same as for power supplies sold separately. This decision is also due to the fact that often the PSU, which is equipped with any case, can be seen on sale separately under its own name.

Today we're going to take a look at the ISO-450PP power supply included with the case. This PSU is manufactured by ISO Electronics (Mingbo) Co. LTD, part of the CWT Group, headquartered in Taiwan, with two factories producing power supplies and converters in China.

Let's proceed directly to the external examination.

General description of the power supply

The power supply is made in a steel case with a thickness of about 0.6 mm, the edges are processed quite well, but not perfectly. There are some fairly sharp edges that can scratch or cut yourself. Burrs, chipped edges and other unacceptable defects are absent. The case of the PSU has a standard gray color, no visible surface defects were also found.

On the outer panel of the power supply unit are located:

• mains switch
• standard power cord connector
• marking of permissible supply voltage (AC 230V)
• 75mm x 75mm stamped air vent.

I would like to additionally note the well-known disadvantage of stamped gratings of holes compared to ventilation holes closed with mesh or wire - this is a higher noise level that occurs when air passes through them, and also, often, a reduction in the usable area of ​​the ventilation hole itself.

On the back panel are:

• a hole for the output of power wires with a plastic gasket that protects the wires from abrasion against the PSU case
• 23 vents 28x3mm.

Additional vents designed to cool the passive PFC module are located on the top, relative to the main printed circuit board, and on one of the side walls of the PSU case.

• 24 pin ATX connector - monolithic. The length of the wires to the connector is 33 cm, after 24 cm from the body a plastic tie is installed on them.
• 4-pin ATX12V connector, wire length to the connector is 35 cm, a plastic tie is installed at a distance of 24 cm from the PSU case
• 1 SATA power connector, the length of the wires to the connector is 34 cm, the cable tie is installed at a distance of 24 cm from the PSU case.
• 2 Molex connectors - wire length up to the 1st connector 34 cm, up to the 2nd - 14 cm, the tie is installed at a distance of 24 cm from the block body
• 2 Molex connectors plus a power connector for FDD - wire length up to the 1st connector is 34 cm, up to the 2nd - 14 cm plus another 14 cm to the FDD connector, the tie is installed at a distance of 24 cm from the PSU case

In total, to power devices inside the system unit, the following are provided:
• 4 Molex connectors
• 1 power connector for SATA devices
• 1 x FDD power connector

A common plastic tie is installed on all wires directly near the PSU case.

Wires for connecting external devices and ATX connectors are used with a cross section of 18 AWG, which is quite enough for this power.

This power supply model uses a sleeve bearing fan manufactured by Xinruilian model with a maximum current consumption of 0.11A and a rated rotation speed of 2500 rpm.

The wire from the fan is connected via a two-pin connector to the main printed circuit board. No circuits controlling the fan speed were seen.

One of the parts of the surge protector is soldered on an additional board, installed on the radiator of the key transistors with the elements down and fixed with two self-tapping screws, the second part is on the main printed circuit board.

The high-voltage part of the PSU uses two 680uF capacitors manufactured by Teapo, designed for a maximum temperature of 85 degrees

The radiators of key transistors and diode assemblies are the same, their base has a thickness of 2 mm, the length of the radiators is 7 cm, the height is 5 cm, the size in cross section is 1 cm. In general, they do not shock with their dimensions, God forbid that they are enough for normal cooling BP elements in the process of work. The direction of the fins coincides with the axis of rotation of the fan, which should have a positive effect on the heat sink. Radiators used are standard F-shaped with double-sided finning. The block provides for the installation of a passive PFC module, it is located on the top cover. A microchip of the type was used as the main controller.

The output circuits are equipped with capacitors manufactured by Teapo, designed for a maximum temperature of 85 degrees with a capacity of 2200uF and 1000uF.

There were no places for unsoldered elements on the board.

The installation is neat enough, however, the wires connecting some of the PSU elements create an untidy look, despite the use of nylon ties.

Power supply testing

So, let's move on to testing.

The ripple test was carried out at 75% of the declared maximum output power in accordance with the distribution of load currents recommended by the manufacturer. Ripple was also measured at the maximum load on the 12V channel.

In general, the ripple values ​​are low and within acceptable limits. So, the maximum ripple value for the 5V channel was 9mV in the first case and 4mV in the second (permissible limit 50mV), and for the 12V channel - 6mV in the first case and 8mV in the second (permissible limit 120mV).

The voltage stability test was carried out on a number of output load currents, calculated according to the principle of their combination within the parameters declared by the manufacturer, but in the original proportions, which are 33, 66 and 100% for each channel of the calculated limit value, taking into account the maximum power consumption on the 12V line. Additionally, measurements were taken in two arbitrary load combinations. As usual, the voltages were measured with True RMS multimeters.

There are no complaints only to the 5V channel, voltage deviations in most cases are within three percent. Voltage deviations on the 12V channel can be considered generally satisfactory, although a couple of times they exceeded the permissible five percent threshold. The voltage value of 3.3V, as a rule, left the zone of permissible values ​​\u200b\u200bwhen the load of this line was more than 6A. In general, the power supply can be considered suitable for use in systems with low power consumption.

At the end of this stage of testing, the temperatures of the radiators were around 50 degrees, and the temperature of the power case was 32 degrees.

To assess the temperature regime of the power supply, additional measurements were taken with fixing the temperatures of its structural elements. Testing was carried out with the top cover of the PSU case closed.

Noteworthy is the high temperature of power element heatsinks at a load very far from the maximum for this unit, and the 80mm fan rotated at a speed of 2500 rpm all the time and provided a very powerful air flow and, unfortunately, no less noticeable noise. According to the test results, we can conclude that the design of the radiators is not well thought out, in other words, these radiators are not suitable for such operating modes.

For the next stage of testing, a computer of the following configuration was used:

• Processor AMD Athlon 64 3000+
• cooler
• matplata
• RAM Patriot LL 512 MB
• Video card Gigabyte GV-N66256DP
• Hard drives: 2 HDD Samsung SP 0812C in RAID 0, HDD WD 1600JD
• Frame

When installing in the case, there were no problems.

For testing, we used: the utility in Demo mode (90 minutes) and the FarCry game (60 minutes). During testing, there were no freezes, reboots, errors, in a word, the system worked stably. The temperature of the PSU was around 40 degrees. In general, the power supply worked for two days without any complaints. The only remark concerns the increased noise level, due to the fact that the fan rotates at maximum speed all the time.

Voltage deviations from the nominal within the normal range.

conclusions

This power supply should not be used with systems that consume more than 250W peak. The disadvantages of the design include small heatsinks, as well as the lack of fan control circuits, as a result of which a high level of noise is observed.

Repair of switching power supply. Any person with basic electronic skills can repair the power supply or voltage converter on their own. Take action, identify the problem and fix it. (10+)

We repair the switching power supply ourselves, with our own hands. Faults

Attention! Some elements of the power supply are under mains voltage during operation. Make sure you are qualified to safely repair the switching power supply.

Diagnostics and repair of a switching power supply in most cases can be performed with basic skills in radio electronics.

Power supply device, step-down converter of mains voltage

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    This page contains dozens of electrical circuit diagrams and useful links to resources related to equipment repair. Mostly computer. Remembering how much effort and time I sometimes had to spend searching for the necessary information, a manual or a schematic, I collected here almost everything that I used during the repair and that was available in electronic form. I hope someone will find something useful.

Utilities and reference books.