Peak detector is not working when there is change in voltage.

[veerubiji]

Hi,

I am trying to design a peak detector in Multisim simulation tool. I have designed buffered peak detector to get peak voltage of sine signal. The designed circuit is working when signal voltage is constant, for example when signal voltage changes from 1V to 0.5V then it is giving 2V as peak detector output. The designed circuit as shown below.


In the above circuit I am using switch to change the voltage of sine wave from 1V to 0.5V. I am using one more switch to clip negative cycle of sine wave, then i am using buffered peak detector to get maximum voltage.

When i apply 1V sine wave it is working perfectly and giving peak voltage as DC. The problem is when I change signal voltage from 1V to 0.5V then also it is giving 1V as peak. ANy one suggest me what mistake i am doing. I want to design peak detector that will give max voltage even there is voltage variations.

 

[keith1200rs]

How do you reset the peak detect - there is no reset switch or capacitor discharge path?

Keith

 

[FvM]

A peak detector needs a reset mechanism, usually a discharge time constant. Unfortunately it will cause a voltage ripple with constant input voltage. There are more complex circuits to avoid this effect, e.g. using filters, sample and hold circuits. You should start with a specification of intended circuit behaviour.

 

[IanP]

In addition to what was said above keep in mind that the type of OPAM used in your project requires +/- supply to deal with input signals below 0V, so add another 12V source acting as -12V (-V) ..

:wink:
IanP

 

[veerubiji]

A peak detector needs a reset mechanism, usually a discharge time constant. Unfortunately it will cause a voltage ripple with constant input voltage. There are more complex circuits to avoid this effect, e.g. using filters, sample and hold circuits. You should start with a specification of intended circuit behaviour.

I have small doubt if i add resistor to discharge capacitor C1, is there any formula to calculate charging and discharging time. My voltage will vary at every 100 ms thus peak detector has to give max peak? the voltage will vary in-between 0-2V at every 100ms. So how to find the exact values of capacitor and resistor combination? is it 1/2*pi*R*C?