Help Biasing precision rectifiers

[stl_jones@yahoo.com]

I've spent so much time trying to figure this out myself, but I can't

I'm currently using an LM324 op amp, and need to rectify a signal that has a negative peak of 0V and positive of either 2V, or 12V(which ever is easier)

I'll be using this in a car, so my supply voltage is 12V and 0v. I've spent the past 4 hours trying to figure out how to get a precision rectifier to work, and have came up with absolutely nothing.

I've tried all of the rectifiers on this site. **broken link removed**

I think I am having trouble with modifying these circuits to work on an all positive input signal. If anyone could suggest a precision rectifier that would work, and also tell me which values I should be using for the resistors, I'd appreciate it A loT!

 

[audioguru]

Your input never goes negative so why do you need a rectifier circuit?
The circuits you found all have their input going positive and negative. Most use a positive and negative supply.

 

[stl_jones@yahoo.com]

If I use the signal that is 0V to 12V Peak to peak, I want "ground" to be set at 6V, then have the negative alternation from 6V to 0V be rectified.

Now I would have an all positive signal that will be able to drive a load (LED's) with a very high duty cycle, instead of just less than 50% making them appear dim.

 

[audioguru]

You can bias the precision rectifier at +6V to do almost what you want. But the LM324 opamp max output high is about 1V less than its supply voltage.

 

[ronv]

If your current requirement is not to high could you not use a 6 volt zener diode to rectify it?