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Design >> Analog Design >> Over current protection
https://designers-guide.org/forum/YaBB.pl?num=1188897290

Message started by quangtay on Sep 4^th, 2007, 2:14am

Title: Over current protection
Post by quangtay on Sep 4^th, 2007, 2:14am

Hi eve'one,
Can anyone tell me about the "Over current/temperature protection" in a design? If you have a circuit/temp please share with me.
Thanks,
quangtay

Title: Re: Over current protection
Post by tosei on Sep 4^th, 2007, 2:05pm

Hi,

For over current protection, one simple and effective method is to use a sens resistor and a switch in series with the current you want to control and a comparator. That comparator would be looking at the voltage drop accross the sense resistor and would switch when a certain threshold is reached. When this happens, you could do several things. One option is to use negative feedback: the comparator would remain in the linear region and should control the switch in series with the sense resistor. In this way, by means of the feedback the switch would have its on resistance modulated in order to keep the voltage drop accross the resistor constant.

Hope this helps
Tosei.

Title: Re: Over current protection
Post by quangtay on Sep 4^th, 2007, 8:07pm

Hi tosei,

Can you tell me more detail about sense resistor in IC design? Does it have any secial character? (I use Cadence software). Because I want to use it in internal protection. You mean, that I should use the negative feedback signal and compare it with a ref signal. I wonder how to find a stable reference signal? (I think to find a stable signal in IC with high accurate is not easy :-[).

Thank you very much.
quangtay.

Title: Re: Over current protection
Post by Berti on Sep 5^th, 2007, 12:12am

The reference voltage is usually not the problem. An (untrimmed)
bandgap should be accurate enought for an over-current protection
(...and usually a bandgap-voltage is available on every IC).
But the process variation of the sense resistor (normal resistor) can
cause large variation. But there you can find many publications dealing
with that problem.

Cheers