Output OVP of tOP switch
Hi,
I have designed an 24V 1.5 A output power supplyi I use the hysterisis output OVP circuit in PIEXPERT with 30 V zener and BAV20 and 22K,
But when ı increase the output voltage of the Power supply by changing TL431 reference voltage, the output voltage start to increase beyond 36V but after 38V , OVP protection starts,( I decrease the ZD voltage to 24V but the problem does not solved) my safe output voltage limit is maximum 30 V,
How can I solve the problem,
Best regards,
Comments
When I test the SMPS in full load and no load its OVP voltage to enter protection changes, with full load when I increase the voltage its works as expected but in no load condition it doesn't enter OVP.. I thing it is the problem of coupling between Bias and output winding,
May be adding a parallel Optocoupler to normal feedback Optocoupler and adjust it to control the OVP will be solution. but it will be expensive, is there any easy way?
In real life I thing if the feedback voltage resistors and optocoupler doesn't damage when the output voltage increases beyond adjusted value, TL431 reference also increase and TL431 shutdown the SMPS am I right? How does OVP characteristic of the SMPS is tested in real life?
Best regards,
As PI-Cochrane was trying to explain, implementing a primary-side output OVP function is going to have tolerance issues. This is due to: secondary-bias coupling, output load level, bias winding capacitor size, OVP zener tolerance, etc. There are a lot of different variables in this type of OVP implementation.
If you need a fairly precise OVP threshold, PI-Cochrane's advice of implementing a dedicated secondary side OVP circuit is going to be your best solutation. You could do this many different ways but they're all going to involve adding some kind of additional opto component across the safety barrier.
-The Traveler
It should be understand that it is hard to have consistent OVP voltage because of the cross regulation between output and primary side bias. To improve this issue, the coupling between bias winding and output winding is very important, so you may have to modify your transformer configuration.
And if a resistor is connected between bias winding diode and bias cap (normally 1-10 ohm resistor), PLS short it. Try zenners withdifferent voltage rating and try bias capacitor with low value capacitance.
If the SPEC for the OVP is very tight, you may have to use OVP circuit in the secondary side. I mean sense output directly and use optocoupler to trigger the OVP.
PLS upload your schematic, and hopefully I can find something else.