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where to put oscilloscope probe of switch mode power supply
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khatus:

Hello guys i want to measure switching frequency of a 220 to 12 volt dc switch mode power supply.But i am confuse where to put the oscilloscope probes.Can anybody tell me where i can put those probes..






MosherIV:
If you do not know - DO NOT DO IT !!!

These types of smps are incredibly dangerous!
They work by first rectifying the mains voltage to give you 240V DC , with all the energy of live main as well !

Then this is switched/pulsed into the small transformer at high (50KHz or higher) frequency.
The secondary side is rectified into a capacitor.
This voltage is measured and the difference from the setpoint voltage is fed back to adjust the  frequency of the pulses.
The freq or pulse width is adjusted to keep the output voltage (or current for constant current psu) at the correct value.
tunk:
Connect them to the 12V output - the filtering isn't perfect so it should give you some idea of the frequency.
PA0PBZ:

--- Quote from: tunk on August 19, 2019, 07:25:41 pm ---Connect them to the 12V output - the filtering isn't perfect so it should give you some idea of the frequency.

--- End quote ---

Otherwise the anode of D7 should show you what you want, with the ground clip of the probe connected to the negative of the output. But beware, if you don't know what you are doing it can kill you, your scope and your cat!  :scared:
Canis Dirus Leidy:

--- Quote from: khatus on August 19, 2019, 06:53:15 pm ---Hello guys i want to measure switching frequency of a 220 to 12 volt dc switch mode power supply.

--- End quote ---
For some practical purpose or just out of curiosity? In the first case, just look at the datasheet - the switching frequency of VIPer22A is fixed (60 kHz).

P.S. But in any case, poking into the power supply with the oscilloscope (unless PSU is connected to mains through isolation transformer) is a really bad idea.
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