# Voltage Latch/Memory

#### lattesurf

Joined Mar 6, 2007
9
As the title suggests, i'm now stuck with another problem. After solving the DC voltage averaging circuit (see post http://forum.allaboutcircuits.com/showthread.php?t=5075 ), i now need to somehow "latch" or "store" the voltage level.

So for example, i have a DC voltage input of 5Vdc. i need a circuit or IC that can "remember"/"latch"/"store" this 5Vdc, even if the input now drops from 5Vdc to 2Vdc.
The input ranges from 0-10Vdc, so the circuit or IC should be able to "store" any levels within the range.

I tried the capacitor charging method, and the voltage only holds for 1-2seconds before dropping down to 2Vdc. i'm looking for a solution that would last for a longer time, maybe even a few hours. A supercapacitor might work, but again, the charge time would be very long. A maximum response time of less than 2-3seconds would be prefered.

Currently i'm trying to limit the circuit to purely analog, i know it would be a piece of cake using a digital solution.

Thanks for any suggestions!

#### ashokcp

Joined Mar 8, 2007
50
Maybe a low drift peak detector can work. But I am not sure whether it can hold for hours, though! I am giving a link below from National Semiconductors, which has one ckt for a low drift peak detector. Maybe, you could use ultra low leakage capacitor for holding the peak value.

Application Note 31 Op Amp Circuit Collection - AN007057

http://http://www.national.com/an/AN/AN-31.pdf#page=1

Hope this would be useful.

#### nomurphy

Joined Aug 8, 2005
567
If you use an ADC it will convert your voltage into a digital value (byte) that you can store into memory -- which could theoretically last for years with the proper design.

#### beenthere

Joined Apr 20, 2004
15,819
You could look into a sample-and-hold circuit. If the voltage level is critical as to the level and a long hold time, then the A to D and digital storage may be the only way out.