Voltage Comparator

[daveguk]

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

 

[Roff]

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.

 

[daveguk]

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

 

[MrAl]

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.