Applications of diode: Clamper circuit

 

Applications of diode: Clamper circuit

Clamping circuits are basically used to change the DC level of waveforms by using capacitor. Basic principle of clamping circuit is the charging and discharging of capacitor used. In clamper circuit charging time of capacitor is made very small than discharging time. For example if discharging time is 50ms then charging time is 50µs.  To achieve less charging time than discharging time, values of capacitor C and load resistor RL are chosen accordingly.

There are basic two types of clamper circuits

1.     Positive clamper

2.     Negative clamper

 

1.    Positive clamper: In positive clamper circuit values of C and RL are selected in such a manner that values of time constant Ʈ=CRL is very high which causes voltage across the capacitor will not discharge considerably during reverse bias of diode.

During negative half cycle of input signal, diode is forward biased and behaves like short and capacitor will charge rapidly and hence output is “0”.

During positive half cycle of input signal, diode is reverse biased and behaves like open. Since discharging time of capacitor us higher than input signal, capacitor remains fully charged and we get output which is twice of input. Finally output signal is shifted upward. Figure below shows the circuit diagram and input/output waveforms of positive clamper.

Fig: Circuit diagram of positive clamper using diode

Fig: Input (red) and output (blue) waveforms of positive clamper

2.     Negative clamper:  In negative clamper direction of diode is reversed than positive clamper.

During positive half cycle of applied input waveform, the diode is forward biased and behaves like short. Since charging time of capacitor is very small it got charged quickly and we get “0” output across the circuit.

During negative half cycle of applied input waveform, the diode is reverse biased and behaves like open. Since discharge time of capacitor is higher, it remains charged during OFF time of diode and we get output across the circuit which is twice of input but in minus. Finally signal is shifted downward.

Figure below shows the circuit diagram and input/output waveforms of negative clamper

 

Fig: Circuit diagram of negative clamper using diode

 

Fig: Input (red) and output (blue) waveforms of negative clamper

 For detailed explanation of clipper and clamper circuit along with experimental details, please check video.