Using Components Recovered From Old PC Power Supplies

This article is an application from:

https://www.instructables.com/Recovering-Old-PC-Power-Supplies/

which set out to recover the components of old PC power supplies.

Perhaps the most efficient method is to build a new switching power supply from recovered components.

Such a power source is the one we propose to build further. Made around the IC type IR2153, it uses a significant part of recovered components. Once done, such work can be very useful in powering devices with a power up to 200W.

A problem that it can solve would be that of replacing mains transformers (more and more expensive) which are followed by rectifiers and DC voltage stabilizers. Thus, with a power source like this one can obtain a single continuous voltage that can be lowered or raised with other power sources, according to needs (for total powers up to 200W).

From the old PC power sources will be used:

Tr1. chopper-1pc.

C7-1uF-1pc.

C1,C2-220uF-470uF/200V-1+1 pcs.

D1-rectifier bridge-1pc.

NTC-Te1-1pc.

Heat sinks for Q1,Q2, D3-1+1pcs.

Metalic case (if appropriate).

The notations refer to diagram 1.1. It can be seen that these are important components that can be recovered.

The other components are recommended to be new.

They can be purchased from any website specialized in the sale of electronic components according to the list of materials given further in the article.

The device was made in two distinct constructive versions from the PCB point of view. However, the electrical diagrams is the same in both versions. Only the notations in the diagrams differ. The discussion on the schematic diagram will be done in relation to Variant A.

In Photo 1.1 this is given in the case of the mains voltage of 220-230V.

This voltage is rectified by diode bridge D1 (double alternating ) and is applied to C1 in series with C2, on which equal voltages of approx. 160V are obtained.

Sig1(3A) is a protection in case of an internal short of the power supply.

NTC marked with Te1 limits the current when the power source is turned on, current absorbed by C1, C2. After a while, it heats up and reduces its resistance to a few ohms, reducing losses and thus increasing the efficiency of the power supply.

C1, C2, Q1, Q2 form a half-bridge circuit to which diagonal the TR1 chopper primary is mounted.

The operation of this circuit is the same as that of PC power supplies, for this reason the reused components adapt very well to the operation here.

Through R1, D2 (C3, C4 filtering) IC IR2153 is fed to pin 1 (15,6V).

Once powered, the IC oscillates at a frequency given by R2, C5 (ca. 50KHz) and opens into "Push-Pull" Q1 and Q2.

D5 in series with C6 allows that by charging C6 with a voltage approximately equal to that of the IC supply, Q1 can be opened when necessary (the voltage on pin 7 is higher than that on pin 6 when opening Q1).This configuration allows us not to using the transformer driver.

C7 eliminates the continuous current component that inevitably appears due to the asymmetry of the components used, which would saturate the Tr1 core.

The voltage in the primary Tr1 (W1) appears at a lower level in the form of 2 antiphase voltages in the 2 secondary windings W2, W3.

These 2 voltages are rectified by the 2 diodes in capsule D3.

D3 is a fast, high current diode.

C8, C9 (low ESR) filters the output voltage.

For countries where the mains voltage is 110...120V, use the diagram in Photo 1.2.

This differs from the previous one only by the appearance of a new connection, AB, in the mains voltage rectifier.

This causes only two diodes to work in bridge D1, d1 which charges C1 and d2 which charges C2. d3 and d4 are reverse polarized and do not work. A doubling of the mains voltage is obtained, with two monoalternating rectifiers. The voltage on C1, C2 is also in this case 160...165V.

Datasheet for IR2153 is attached below.

At adress:

https://drive.google.com/drive/folders/1eAXpRK6pV5ERyVXqVpY1k-BGFzonQaDY?usp=share_link

the project for Variant A is located. Here you can find the schematic diagram (with bill of materials) and the PCB. The ExpressPCB program was used, a freely available program that allows PCB execution in "home" mode.

In Photo2.0 you can see the PCB as given by ExpressPCB.

Photo 2.1 shows the components before mounting on the PCB.

Photos 2.2 to 2.6 show various stages of mounting the components on the PCB. Tin, tin soldering tools, and cutting pliers are used.

Photos 2.7 and 2.8 show assembled power supplies.

Special attention must be paid to the connection of secondary Tr1 to D3 and to the choice of D3. Wrong connections of the secondaries lead to the burning of IC, Q1, Q2 and Sig1. The incorrect choice of D3 has the effect of destroying it and the previous components.

Choosing D3 is not difficult. For output voltages lower than 15V, SB3045 or equivalent can be used. For higher voltages, the MBR20100 diode or equivalent is recommended.

Choosing and connecting the Tr1 chopper in the circuit is more difficult. For this I will write a more detailed tutorial, which will deal with the analysis of a transformer that we don't know much about or that we want to rewind in the secondary to be used to obtain a certain voltage.

A transformer can be used even without this tutorial if we have some information about how it is connected to the power source from which it comes. It will be noted here how to connect the secondaries to the rectifier diodes and the voltages they deliver.

The respective connection method will be respected. The choice of windings is made considering that those that delivered 5V will now deliver 10..12V, and those that delivered 12V will now deliver 24..29V.

At the address:

https://oshwlab.com/TedyS/sursa-ir2153-m1

we will find the project for Variant B.

The free EasyEda programming environment is used and offers us Schematic Diagram, bill list and PCB that can be ordered from the factory at a convenient price.

Photo 3.0 offers us a 3D image of the PCB assembled under EasyEda.

Photo 3.1 gives us an image of the PCBs as it comes from the factory.

Photo 3. 2 makes a comparison between PCB Variant A and B. It can be seen that VariantB is more compact.

Photo 3.3 shows the components necessary to assemble a PCB in Variant B.

Photo 3.4 represents an assembled power supply, with the radiators arranged horizontally. If there is available space, the 2 radiators can be mounted in this way, on a common support, possibly metallic, which provides good cooling and mechanical rigidity.

If there is no available space, the 2 radiators are mounted vertically, as in Photo 3.5. It is a more compact assembly.

In the case of Variant B, it can be seen on the Schematic Diagram and on the PCB that any of the secondary pins of Tr1 can be connected to the anodes D3, through two wires. This gives great flexibility in using a varied range of chopper transformers. But special attention must be paid to the way the connections are made, as there is a danger (as in the previous case) of destroying components in case of a mistake. We must also be careful when choosing D3, as in the previous case.

Some time ago a friend asked me to solve the following problem: he had a car refrigerator (12V supply) that he used in portable mode, on trips. Overnight, it could not be left unsupplied with voltage (the content can be altered) but it also cannot be left in the car, because due to the high consumption (8-9A) it can discharge the car battery. Hence the need to be taken into the room and powered overnight at 230V.

The idea of building a power supply comes naturally, as in the previously discussed cases, but in a box.

I used Variant A of the power supply.

I used a recovered metal box as in the link in the Introduction. This is cover with a sticker (green) bought from DIY stores.

Photo 4.1 shows the front assembly. A car cigarette lighter adapter was mounted here. The load is connected to it, in our case the refrigerator.

Photo 4.2 shows the rear assembly. The coupler for the 230V power supply network and the original fan have been kept here. The latter is powered at 12V provided by the power supply.

Photos 4.3, 4.4, 4.5 show the general assembly of the power supply.

Connections are made with wires of minimum 1.6 mm diameter, insulated.

Note that in this case Tr1 has been rewound in the secondary, to obtain a voltage of 12V.

Many years ago, when I started working on switching power supplies, I was greeted with announcements such as:

"Switching power supplies are not for beginners!"

If I had thought like that, I wouldn't have done anything. Neither in this nor in others.

However, it should not be overlooked that switching power supplies are not only difficult, but also carries a fairly high risk of life-threatening incidents.

The safest method of protection for a beginner is to use the supervision of a person with experience in the field. I recommend this way.

Another way to reduce the risk of electrocution is to use a 1:1 isolating transformer as in Photo 5.1. It can be used at the power supply input both at 120v ac and at 230V ac, power up to 400W.

To measure the parameters of the power source, a (old) resistive load like the one in Photo 5.2 can be used.

It is actually two resistive loads, each of which can be: 4, 8, 12, 16 ohms. Each load supports max. 5A.

In various combinations, these loads can be connected (with thick wires) to the output of the power supply. With a digital multimeter you can read the output voltage of the power source. Of course, other suitable loads can be used.

Using these tools, the following results were obtained:

1.

No load, Uout=13,5V

Load=2ohms, Uout=12,8V, Iout=6,4A, Pout=82W

2 loads of 4 ohms were used in parallel, to admit 10A.

2.

No load, Uout=28V

Load=4 ohms, Uout=26V, Iout=6,5A , Pout=169W

2 loads of 8 ohms were used in parallel, to admit 10A.

The efficency of the power supply is in all cases over 85%, that is, very good.

And that's it!