Triangular, Saw tooth and pulse waves are typical examples of non-sinusoidal
waveforms. A conventional AC voltmeter cannot be used to measure these
sinusoidal waveforms because it is designed to measure the RMS value of the
pure sine wave. One possible solution to this problem is to measure the peak
values of the non-sinusoidal waveforms. Peak detector measures the +ve peak
value of the square wave input.
During the positive half cycle of Vin:
o/p of the op-amp drives D1 on. (Forward biased)
capacitor C to the positive peak value Vp of the input volt Vin.
During the negative half cycle of Vin:
is reverse biased and voltage across C is retained.
only discharge path for C is through RL since the input bias IB is
proper operation of the circuit, the charging time constant (CRd )
and discharging time constant (CRL) must satisfy the following
Rd = Resistance of the forward-biased diode.
= time period of the input waveform.
>= 10T (2)
RL = load resistor.
RL is very small so that eqn. (2) cannot be satisfied.
a (buffer) voltage follower circuit between capacitor C and RL load
is used to protect the op-amp against the excessive discharge currents.
= minimizes the offset problems caused by input current
conducts during the –ve half cycle of Vin and prevents the op-amp from going
into negative saturation.
-ve peak of the input signal can be detected simply by reversing diode D1