Voltage Comparator

Hi everyone.

I am designing a power supply/battery management circuit and have come across a problem I have not met before.

I want to enable/disable the smoothing reg depending on the input voltage. The regulator should only turn on when a stable 9V is detected.

**broken link removed**

My question is - what IC could be used for this purpose? A point in the right direction is all that is required.

Many thanks,
Dave

A part number for the buck regulator, if it is an IC or a packaged product, would be helpful. A full schematic would be better.
It is always better to provide too much info, rather than too little.

Hi Ron,

Thanks for your reply. I am using a Linear LT1765 9-5V step down buck switching regulator. Datasheet link:

https://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1032,C1064,P2154,D3864

This reg has a SHDN (shutdown) pin - the regulator turns on when the pin's input is high and off when low. The threshold for the pin is (min-ave-max) (1.27-1.33-1.40) whereas I only want the regulator to turn on between say (8.8-9-9.2).

I was thinking about a potential divider using two resistors so that the common of the two is at 1.33V when V+ is at 9V:



This solution doesn't seem very elegant though. I also don't know what would happen if the voltage is >9V and therefore >1.33 at the SHDN pin. The datasheet quotes the max SHDN threshold as 1.4V but I don't know the results of providing more than that.

Many thanks,
Dave

Hi there,

An LM339 with four comparators on the chip comes to mind, or LM393 which only has
two comparators. A few resistors also, and a zener diode for a reference.
With the either chip you would have enough comparators to build a small delay circuit
too, so that the enable is delayed for short time after the 9v supply comes up.