Thread: Looking for undervoltage lockout circuits!

If there is no Zener diode devices,How to design undervoltage lockout circuits?


Best regards,

most times uvlo simply uses a comparator with a little hysteresis. VDD is divided down (say in half), and compared to the bandgap voltage. (Say 1.25v) Now your uvlo trips when VDD = 2Vbg or 2.5v. There ya go.

Do you have a bandgap? If not it's a little trickier..

I also suggest you use a simple comparator .use devided Vdd compared with a stable reference.it must need a reference voltage.

qutang - please don't repeat answers, or post junk. it really bothers me.

Originally Posted by electronrancher

most times uvlo simply uses a comparator with a little hysteresis. VDD is divided down (say in half), and compared to the bandgap voltage. (Say 1.25v) Now your uvlo trips when VDD = 2Vbg or 2.5v. There ya go.

Do you have a bandgap? If not it's a little trickier..

Hi, what if the supply voltage drops to a level that both bandgap and comparator are not able to work, at this moment, the output signal is uncertain, it will be 0.6v or something like that, so how to make sure when VDD drops (under 2Vbg in your case), the UVLO circuit can give a reliable 0V output? Thanks.

hi,cmosbjt

you can use pull up Res to fit your request

you need a "UNDERVOLTAGE SENSING CIRCUIT". you could use an IC like MC34064. i advise you to check spec sheet of MC34064.

-Erkan

how can i do if for high voltage?if i dont' want to waste so much current the voltage divided, another method?as long as i don't want to draw a big resistor in my IC also
thanks

up to about 12v, i usually see resistor dividers of a few hundred k. other alternative is if you have an internal regulated supply voltage, do uvlo on that rather than on the input.

what is your uvlo voltage you want?

I don't see how you can do away with some form of potential divider. it can be resistor/mos. use natural mos for higher thresholds.

How can i include hysteresis?
Is it sufficient to introduce hysteresis in comparator? or i have to introduce it externally?

If externally, how to include it?

Look here

http://cdn.vicorpower.com/documents/...OV_APPNote.pdf

cheers