The Power Supply Modding Guide (or TL494 -> Anything)

[Th3_uN1Qu3]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

Tweaking the voltage divider at the pin 4 is not a good idea, the voltage there is already near the lower threshold of the Disable-UVP function. Lowering the voltage will only void the short circuit protection!

Also, from what i see, unfortunately pin 12 only affects the powergood signal, so it would be no good for shutting down the supply. I don't think disabling the UVP would have any adverse effects - as long as a short on the output causes pin 4 to go above 1.25v, it will still trigger the OPP and in effect, do the same thing.

Another thing, the error amp in the WT7520 has its inverting input biased to 2.5V, as mentioned in the datasheet. Dealing with this kind of error amp, what is the best approach to take? It doesn't seem feasible to apply the 2pole-2zero compensation circuit, or I missed something?

Of course you can - just put the second RC pair over the top resistor in the feedback divider, it doesn't matter if it goes to the noninverting rather than the inverting input.

[badcoils]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

Hmm...wouldn't it be too "late" if the overpower protection is used for short circuit protection? It has a capacitor after the diode that samples the peak voltage from the base drive transformer, which will delay for quite some time before it shuts down the supply I don't want to replace the transistors if the cheap power supply blows!

Of course you can - just put the second RC pair over the top resistor in the feedback divider, it doesn't matter if it goes to the noninverting rather than the inverting input.

In fact I already did so. But I thought there are some other ways that won't affect the bode plot of the stage...

[Th3_uN1Qu3]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

Hmm...wouldn't it be too "late" if the overpower protection is used for short circuit protection? It has a capacitor after the diode that samples the peak voltage from the base drive transformer, which will delay for quite some time before it shuts down the supply

What value does the cap have? If there's no resistor in series with the diode, either on the transformer side or before the cap, and the cap is 10uF or under, that will react pretty quickly. The reason the cap is there is to prevent switching noise from falsely triggering the protection circuit.

[panos1]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

hi...
it's my firts post here...
i have a pc psu with tl494....
i want to make you board with tl494 but i dont know where i will conect it at the psu pcb...
please can you help me?
i mean that i don't know at which pins of tl494 i will conect your pcb..
i want to convert the psu to an unregulated power supply for a class d amp...

[mariushm]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

Download the datasheet for TL494 , search the internet for combinations of "application note" and the word TL494, read how TL494 works.

It won't help you at all if we just give you some schematic. Need to understand what the chip works and where each pin connects to, then you'll understand how to use it.

[panos1]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

thank you for your reply...
i don't want any scheme...
i just want someone to tell me where i will conect eror amp1-eror amp2-protection...
for start i don't want any protection...
i just want to make the smps work...
after if everything is ok i will add protection....

[budm]

Re: The Power Supply Modding Guide (or TL494 -> Anything)

@PANOS1, if you do not want protection then you do not connect the feedback for the over current, just ground that sensing line. Since we do not have the diagram of the circuit you wan to build, then I gave example of the application notes of the IC, you will still need feedback control for voltage output regulation.
App notes and spec sheet gives lots of info.