Diode Clipper

Clipping means a small piece trimmed from something. The same function we get from a diode when it is used to trim a certain value of voltage or not allow voltage to increase beyond certain level. Just like a rectifier circuit where diode allows one half of AC cycle to conduct through the load. But here diode clipper or diode limiter allows only a part of it.(see fig-1)

Fig-1: Output of a diode limiter

Its potential application are those circuits which do not want to increase a voltage or signal from certain threshold level

Recall rectifier circuit where diode is connected in series to the load here the diode is connected parallel to the load. Based on the direction of connection of diode, the limiter circuit is divided into following two types

1. Positive Limiter

Refer fig-2A to understand the application of diode as positive limiter

Fig-2A: Positive Limiter

In the above circuit the diode is off within 0.7 V, so no voltage drop takes place at resistor R.  Hence potential difference between points A & B is 0.7.

After 0.7 V diode is forward biased and conducts. So voltage drop takes place across the resistor. hence we get final output for the positive half cycle as below:

Fig-2B: Diode becomes a shunt in diode limiter circuit

When negative half cycle comes the polarity at the both ends of the diode changes so the diode becomes reverse bias. Then again there is no voltage drop takes place across the resistor. Hence we get the output voltage same as the input voltage i.e Vin = Vout. See fig-2C

Fig-2C: Diode is off at -ve half cycle

2. Negative Limiter

In negative limited circuit the function of the diode is same as positive limiter. But here instead of clipping positive half cycle diode is clipping negative cycle. We just reverse the direction of the diode by 180° in the circuit. See fig-3 for the final output of the circuit

Fig-3: Negative Limiter

Both Half Cycles can be clipped:

We can trim the both half cycles by connecting two parallel diodes in reverse direction. See Fig-4

Fig-4: Positive limiter and negative limiter in the same circuit

Now when positive half cycle comes diode D2 conducts and and clips off the voltage above 0.7 V. For the negative half cycle diode D1 conducts and clips off the voltage below – 0.7 V.

Bias Diode Limiter

With bias limiters we can trim the output voltage as per our requirements.  we just add a voltage source in series to the diode. See Fig-5 below

Fig-5: Bias Diode limiter for positive cycle

To clip from a certain positive level we added a bias voltage in series to the diode. After V1+0.7V diode will shunt so above voltage levels will be clipped off.

Similarly we can cut voltage from certain negative levels. In that case diode must be connected as in fig-6

Fig-6: Bias Diode limiter for negative cycle

Complete Video Lecture on Diode Clipper in Urdu/Hindi