Troubleshooting and repairing Switch Mode Power Supplies

How Switch Mode Power Supply works

Understanding The Functions Of Switch Mode Power Supply

Troubleshooting linear power supply is extremely straightforward as opposed to SMPS or switch mode power supplies. AC voltage gets into the primary part in linear transformer after which modified the AC in a decreased or increased AC voltage with regards to the second transformer winding.

The result AC voltage is after that rectified and also filtered using a diode and electrolytic capacitors to generate a nice and clean DC voltage. Whenever you have a fault within the linear transformer circuit, We can declare it is not hard to find the problem. It is certainly different when it comes to an SMPS power supply in LCD televisions for example or a computer ATX power supply. The concepts tend to be challenging and several technicians seen it pretty tricky to completely know how the switch mode power supplies function.

The operating process of SMPS power supplies differs from linear model. Initially the AC voltage is going to get into a full wave bridge rectifier that generates a DC output which will be filtered utilizing a big capacitor generally 220 uF and until 450V.

SMPS power supply

The clean DC voltage will after that go to start up resistors as well as the input of switch mode transformer. When the voltage crossed via the high ohms start up resistors, the voltage will decrease to a value in which after that gets into the VCC supply pin of the PWM IC or the Pulse Width Modulation circuit.

As soon as the PWM IC obtained the voltage, it’s going to produce a signal to drive the FET transistor and generates a varying within the magnetic field on the transformer primary winding. This changing magnetic field in the primary induces voltage in the secondary windings.

Every one of these AC voltage generated by the secondary windings will be after that rectified, filtered, and finally regulated to make a clean DC voltage. In a Monitor or TV Circuit, one of the main DC output voltage is the B+ that supply to flyback transformer.

SMPS output voltage

The output from the B+ voltage is next linked, via a “feedback” loop (which contain an optoisolator ic and an error amplifier TL431 IC), back to the PWM IC. Once the voltage through the B+ supply increases or decrease a bit, the Pulse Width Modulation IC is going to take action to adjust the output. You need to question yourself precisely what is the aim and the functionality of the electronic components in the SMPS power supply circuit and the right way to verify them in case they fail. Discover the functions of each element in the switch mode power supplie circuit:

  • Bridge rectifier
  • Filter capacitor
  • Start up resistors
  • Chopper/Power FET
  • Pulse Width Modulation (PWM IC)
  • Current sense resistor

Bridge rectifier

  • Switch mode power transformer
  • Optoisolator/optocoupler
  • Error Amplifier IC (TL431)
  • Secondary inductors
  • Secondary diodes
  • Secondary filter capacitors

output capacitors

Motivate your self further more through exploring the web for PWM IC part number datasheet document. For instance, UC3842 circuit is usually found in SMPS power supplies. Have you learnt precisely what the job of pin 5 of that PWM circuit is? Have you any idea what is the exact voltage which gets into the switching IC? Have you learnt what pin is the VCC supply voltage? Have you any idea which pin number that drives the power transistor FET? Will i find a substitution for this circuit? Etcetera…

Feedback circuit

Why don’t we take a soldier to illustrate. Soldiers not just excellent in handling rifle but additionally understands every detail regarding it. They understand how to dismantle and gather again the rifle rapidly. These people know the amount every bullet value, how large could be the size of the bullet, what lengths the firing range, etc… Wish nobody get tired of the soldier’s example, could you get the concepts?

Power board

Whatever power supply which arrives to the repair bench, I would certainly not instantly repair it, actually I may get a few moments to examine the circuit design to check it through every sides prior to I start to fix. SMPS troubleshooting isn’t restricted to a single technique actually several electronic repairers technicians own their own methods and strategies to fix  switching mode power supply problems. A lot of them choose to utilize light bulb to isolate SMPS faults and some decide to employ resistors. Troubleshooting switch mode power supply is exciting and adaptable however in a few situations might make you get extremely distressed as well. Bear in mind, never restrict yourself to simply a couple of sources to to help you get understand and be capable to repair SMPS power supplies. If you possess a budget, obtain the training books which have based on SMPS repair guides and begin performing practical over it. Discuss your difficulties with other electronic repairers and the essential issue is never stop trying. There are many mountain within the path of our live and you oneself must climb and beat it. Good luck!

Troubleshooting and repairing Switch Mode Power Supplies
LCD Monitor Repair Secrets
Electronic Repair Information

Check Also

Electronics Projects: Configurable RS232 To TTL To I2C Adaptor

RS232 signals cover a much longer distance than standard TTL and I2C signals. Also, RS232 …


  1. I would like to know more details about smps cct.pls help me.thanks

  2. I have to say that this is really a good influencing look at thios particular subject matter.

    Im really pleased yoou shared youur thoughts plus smart ideas
    annd I discovered I somewhat agree. I seriously like your
    clear writing additionally , the efforts you might have
    used writing this submit. Numerous thanks yous for your
    strong work and very good luck with your website, I most certainly will
    be awaiting new pieces within the future.

  3. Thanks for taking your time to write this. I enjoyed reading it, and especially liked the labeled pictures.

Leave a Reply

Your email address will not be published.