mod an atx supply with the at2005 chip.

[Damien]

Hey there

I'm trying to mod an atx supply with the at2005 chip.

I've put a 50k pot between 12v rail and ground with the wiper going to pin 2 (voltage adjust)

Problem is that as soon as it hits about 13 volts it shuts down due to I suspect over voltage protection circuitry.

Is there a way of disabling this?

Your help would be appreciated, thanks in advance -

knifey

 

[GPG]

Is pin6 floating?

 

[Damien]

Hey GPG

Yeah I dissconnected pin 6 and grounded it with a 1k resistor but still doing the same thing.

Another guy I spoke to on a forum suggested that you have to use the preset resistors (variable pots forming voltage dividers) on the other pins to stop the chip from shutting down, as it senses all 3 outputs. He said to set pin 3 to 3.5, pin 5 to 4.5 and also to connect pin 4 to 15.

Well, sounds like he knows more about this than I do haha.

I guess I'll try that next.

 

[GPG]

Yeah I dissconnected pin 6 and grounded it with a 1k resistor

Floating means no connection.

 

[rickselectricalprojects]

Hey there

I'm trying to mod an atx supply with the at2005 chip.

I've put a 50k pot between 12v rail and ground with the wiper going to pin 2 (voltage adjust)

Problem is that as soon as it hits about 13 volts it shuts down due to I suspect over voltage protection circuitry.

Is there a way of disabling this?

Your help would be appreciated, thanks in advance -

knifey

i had a cheap atx psu with an AT2005 chip, it dosent work anymore but i can take some photos of the parts around it if it would be helpful.

 

[Damien]

Ohh ok I learnt something today. Thanks guys I havn't had a chance to look at it but when I do I'll let you know how it all goes. =)

 

[Damien]

Got it to work but short circuited it and now it won't turn on anymore =(

I guess it has no short circuit protection now. :/

I got variable voltage though and set the potential with a trimmer pot to go from 12v to 15v for charging batteries with a small 240v generator while camping.

Could I have fried the mosfets? I will check them tomorrow.
Hopefully that's all it is otherwise it's going in the bin. I spent 5 hours on this thing. I just hate it when stuff like this happens.

 

[davenn]

Floating means no connection.

how did you determine that grounded means floating ?

 

[GPG]

The pt pin-says lower than .6v or above 1.2v protection of under/over voltage is activated. Its biased internally so I took a shot that floating it would work I still don't know what the result is/was

 

[Damien]

how did you determine that grounded means floating ?

I guessed. Now I know it means isolated. =)

 

[Damien]

GPG: I'm wondering if setting up a voltage divider with a pot to set the pin at a specific voltage would work?

 

[GPG]

Try it and see, then you can tell me!

 

[Damien]

No can do! I blew my psu up lol
If I come across another one, I'll come back to this thread but that could be years of months down the track. Watch this spot lol. =P

 

[Damien]

Hey guys just while I have your attention and we're familiar with one another I was wondering if someone could answer a completely un-related question for me.

In the circuit diagram I have provided (I'm using it for a class ab guitar amp) I have read that when using a darlington pair the total current gain of both transistors is just one multiplied by the other so if I use (Just for the NPN side to simplify things)
Tip41c which has a current gain of 75 to drive a 2n3055 which has a current gain of 25 I think it was I'd end up with a total current gain of 1125 which is great I guess as I'm looking for more loudness or D.B (more current) as I have the voltage gain side of it sorted with an op amp.

My power supply is 50v rail to rail or 0 to +25 and 0 to -25 in total.

If I use these same resistors I'm going to have an idle current of er.. 9 amps. Is that right?

I'm having trouble working backwards with the maths but I think I calculated something in the ballpark of two 150,000k
to give me a few milli amps of current flowing at idle.

I suck at maths and slipped through the cracks at school due to my autism but I am willing to learn more if I have to.

I was thinking around 30ma would be good for stray idle current for best efficiency with minimal distortion.

So far I've got 25V divided by 150,000 ohms = 0.00025a at the tip41c's base but that times 1125 ends up being 0.0281a (28ma)

Is that right? Should I use 150k resistors?

 

[Damien]

Oh almost forgot

Here are the datasheets for both transistors (Just for the NPN side) I'll copy whatever is decided for the PNP side.

Tip41c - https://www.fairchildsemi.com/datasheets/TI/TIP41C.pdf

2n3055
http://www.onsemi.com/pub_link/Collateral/2N3055-D.PDF

Am I heading in the right direction to get more punch from my amp than using just the tip41 and tip42 complementary pair by themselves (not darlington) providing I have already taken care of voltage gain?