Switch mode power supply. Help!

[juh1]

I tried repairing a switch mode power supply. Whenever I measure the output, it gives the expected voltage rating. But when I supply it to a load, it does not give anything. What can be the problem? Please help. Thank you!

 

[buzzelectrician]

In order to pinpoint the problems as quickly as possible, you must first learn as much as possible about voltages and waveforms in multiple sections of an SMPS unit.

Once you’ve fully comprehend these critical points, you’ll be able to solve all sorts of switch mode power supply repair problems.

Vital Tip (2)

As a precautionary measure, you should conduct multiple tests without plugging in the equipment. An ohm meter can be used to determine whether the power supply failure is caused by short cicuits.

Electrical devices like LCD TVs contain power supply with semiconductors that can be measured with an ohm meter unit.

Vital Tip (3)

If you can’t find the voltage of a zener diode (lack of marking), then use a zener diode tester to help you out. This tester is primarily used for determining the exact cause of a zener diode however…

You can use it on other components as well! That’s right my friend. You can actually use tester on your SMPS voltage regulator, schottky diodes and more!

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[Johnsteave7]

A switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.
All three fundamental topologies include a MOSFET switch, a diode, an output capacitor, and an inductor. The MOSFET, which is the actively controlled component in the circuit, is interfaced to a controller (not shown). This controller applies a pulse-width-modulated (PWM) square-wave signal to the MOSFET's gate, thereby switching the device on and off. To maintain a constant output voltage, the controller senses the SMPS output voltage and varies the duty cycle (D) of the square-wave signal, dictating how long the MOSFET is on during each switching period (TS). The value of D, which is the ratio of the square wave's on time to its switching period (TON/TS), directly affects the voltage observed at the SMPS output. This relationship is illustrated in equations 4 and 5.

I’m recommending you to visit transistor because boths are switching device and perhaps you could check out  of this.