How to remove protections from SG6105?

[m111920]

I want to remove all protections from SG6105 powered ATX PSU,
I have removed all wires except +12v and I will use this PSU for powering 12v stuff



I want to remove protections and everything because PSU won't work without proper voltage on vsense pins.

[999999999]

Re: How to remove protections from SG6105?

Normally a person would put a dummy load on the 5V rail to keep it from drifting to an excessively high voltage, something like a 2 ohm, 20W power resistor on a heatsink.

That controller chip has a built in voltage divider so there isn't an external one that could be modified as with some designs. Instead you must give it a fake reference voltage and since it will be regulating based on 12V rail load, that is the rail you would use for the fake reference.

What you can do instead is sever the signal line leading to the controller V5 pin, the one which senses 5V rail voltage. After that line is cut, use a resistor divider circuit from the 12V rail to cause 5.0V to be sensed when the 12V rail is 12.0V.

See the following page which is a voltage divider calculator. http://www.calculatoredge.com/electr...e%20divide.htm Ra resistor would go in series from the 12V to the controller signal pin V5 and Rb would go from
a point between Ra and V5 pin, to ground.

You can input the 12V source "Vin", 5V output "Vout", then pick a few thousand ohms resistor for "Ra" and it will tell you the "Rb" value you need. It is up to you to determine if you have acceptable resistor values at high enough precision to get close enough to 5.0V. For example if you had a 6K8 (6800ohm) "Ra" and a 4K7 "Rb", you would get close to 4.9V. If that is close enough you are done. If it is not close enough you need to use a little lower value "Ra" with a high precision rating, something less common so sources from an electronics supply house.

If after doing the above for the 5V rail sense circuit you find that it still needs the same done for 3.3V, repeat all the above for that rail and V33 sense pin, to divide voltage down from 12V to 3.3V.

[m111920]

Re: How to remove protections from SG6105?

Isn't there a way to disable it completely as SG6105 is TL494+ two 431 in one chip.
I have already removed 3.3v and other components and I don't want to solder it back

TL494 is very simple, just unsolder a few pins(13, 14 and 15 i think) from board and protection is disabled..

[999999999]

Re: How to remove protections from SG6105?

I wrote nothing about adding back 3.3v. On the contrary you are to sever the 3.3V and 5V, effectively getting rid of both then using a voltage divider between the 12V rail and each detection pin.

You are welcome to try doing whatever you can think of instead of my suggestion. I did not read the entire datasheet, only enough to come up with the potential solution I mentioned.

[999999999]

Re: How to remove protections from SG6105?

Edit for more clarity:

I wrote nothing about adding back 3.3v. On the contrary you are to sever the 3.3V and 5V traces leading to their respective voltage sense pins on the controller, effectively getting rid of both so you don't need the components specific to those rails any longer, then using a voltage divider between the 12V rail and each detection pin to lower the 12V to 3.3V at the 3.3V detection pin and lower 12V to 5V at the 5V detection pin.