Hello guys.
I’ve closed below circuit.
And I see this figure in oscope. Does somebody know where my problem is?
Very thank you.
It looks like the power supply is shutting down due to what it thinks is excess current.
This waveform is known as “ motor boating “ it is a result of supplying a voltage, too much current being drawn and so shutting down. When it is shut down then there is not too much current being drawn and so it starts up again.
It looks like you have got the feedback from the current sensor set to too much.
Thanks Mike.
Now everything is okay, just one problem,the Thyristor is getting so hot.why?
He's Mike. I'm Mark!
No thyristor there, just a high voltage zener diode - which will obviously get a lot of power
dissipated in it due to the high voltage once it starts to conduct.
I presume the secondary circuit keeps the transformer voltages low at startup, but once C6 is
charged enough the zener on the primary will start to conduct and limit further voltage rise.
However all the power is then being dumped into the zener.
Perhaps the zener is kicking in too soon, so that the voltage feedback via the opto coupler
isn't high enough to get the chip to ease back on the switching power?
The zener's main purpose is to prevent over-voltage damage to the switching element.
I'd also check that C2 is doing its job and not letting inductive spikes from L2 through to
the primary circuit
I look up the TNY274PN and its datasheet and find a similar circuit where that device has a
part number, P6KE150A, which is a 150V TVS diode, rated for upto 5W on large heatsink, and
150V nominal, not 130.
Is that the device you have?
https://www.power.com/sites/default/files/product-docs/tny274-280.pdf