Introduction to Clamper Circuit, Diode Clamper Circuit Analysis


In this video, I will talk about clamper circuit, its classification, and working principle of a clamper circuit. So, what is a clamper circuit? Clamper circuit is a network, that consists of diode, resistor and capacitor. And it shifts the dc level of any ac signal or alternating voltage. So, clamper circuit is a circuit that consists of diode, resistors, and capacitor and it shifts the dc level of an alternating signal. Remember, a clamper circuit does not change the waveshape If I apply any sinusoidal voltage in the input side, I will get another sinusoidal signal in the output and it does not change the peak to peak value. Another thing, if we want to make any further shift in the dc level, we can do that by adding external bias voltage – either in positive direction or in negative direction. Now, assume I have an alternating voltage It has a positive peak at +5V, and negative peak at -5V. Therefore, it has a peak to peak value of 10V. Assume, I applied this sine wave in a positive clamper circuit. Positive clamper will push up the dc level of the alternating voltage so that it’s negative peak touches the horizontal axis or the time axis. This is the output of the positive clamper. In the input voltage, the dc level was at zero. The positive clamper pushes up the dc level of the alternating voltage, so that the negative peak of alternating voltage touches horizontal or time axis, and so the positive peak is at +10V. As a result, the dc level of alternating voltage will be at +5V. So, initially dc level was at 0V, and due to shift, the new dc level will be at +5V. Therefore, positive clamper will push the dc level in upward direction Okay.. Now let’s say I have another alternating voltage. This is also a sine wave with positive peak +5V and negative peak -5V.. Therefore, peak to peak value of 10V. Now, If I pass this input voltage through a negative clamper, negative clamper pushes down the dc level in downward direction. As a result, positive peak touches the horizontal or time axis. Now, look at this waveform. If the positive peak touches the horizontal axis, the negative peak will be at -10V. Therefore, the new dc level will be at -5V. So, negative clamper shifts the dc level in downward direction , and positive clamper shifts the dc level in upward direction. That’s it. Negative clamper pushes the input in downward direction, so that the positive peak touches the time or horizontal axis. So, negative clamper shifts dc level in negative direction. In conclusion, we are applying a sine wave at input, and getting another sinusoidal voltage at the output. Input has peak-to-peak value of 10V, and output has peak-to-peak value of 10V. So, a clamper circuit does not change the waveshape and peak-to-peak value of applied voltage. Now, I will talk about the working principle of a clamper circuit. A clamper circuit consists of a diode, a load resistor RL and a capacitor. A clamper circuit is working based on the charging and discharging of the capacitor. The capacitor is charged when the diode is in forward bias, and is discharged when the diode is in reverse bias. Now, let me clarify. This is the structure of a basic clamper circuit. If the diode is in upward direction, that will be a positive clamper and if the diode is in downward direction, that will be a negative clamper. If I apply an alternating voltage here, During the positive half cycle, this terminal will be positive and this terminal will be negative. As a result, the diode will be in forward bias. When the diode is in forward bias, we can replace that with a 0.7V source in series with forward resistance Rf. Usually, Rf varies from 1 to 25 ohm. If we consider Rf=1ohm, a current I starts flowing in indicated direction. As the current gets into this point, current I has two paths to divide. One way is through 1ohm resistor and another way is through load resistor of 50k. As current follows low resistance path, therefore we can assume all the current will flow through forward resistance Rf, and the capacitor gets charged. As the diode is on, we can replace it with short path (ideal model) or a low resistance path of 1ohm. And the capacitor gets charged. As the capacitor is charging this way, we can calculate the charging time constant , by using the forward resistance Rf and capacitance C. That means, τ=Rf *C=1*1E-6=1μS. Total charging time is 5 times of charging time constant τ. So, τc=5*Rf*c=5μS. So, I can conclude that when the diode is in forward bias, the capacitor would get charged instantly. During the positive half cycle, This terminal will be negative and this terminal will be positive respectively This will put the diode in reverse bias. and when a diode is R.B., we can replace that with an open circuit, As if it does not exist in the circuit. The capacitor is holding a a voltage Vc across it. As the diode is in reverse bias and is acting like an open circuit, Therefore, the capacitor will get discharged through the load resistor RL So, the discharging time constant is τ=RL *C=50E3*1E-6= 50mS. The total discharging time for the capacitor is 5 times of the discharging time constant. So, τD=5 RL*C=250ms=0.25 sec That means, it will take only 0.25 seconds for the capacitor to fully discharge through the load resistor. That means, during the positive half cycle of the applied voltage, the capacitor holds up a voltage Vc across it. The operation of a clamper circuit is based on the fact, that the charging time of a capacitor is made very very small compared to discharging time (5us

15 thoughts on “Introduction to Clamper Circuit, Diode Clamper Circuit Analysis

  1. Finally a perfect explanation on cap charge/discharge and TCs. I was stuck trying to
    figure it out using electron flow. now i understand! thaanks

  2. Sir,i didn't understand that how is charging or discharging time is 5 times times constant.??.plzz explain me the logic behind it!!!

  3. When capacitor starts charging and its two plates are charged, those stored charges in plates opposes taking out and delivering electrons it those plates. So it takes longer time for the capacitor to be fully charged.
    a capacitor takes 5 time constants to get fully charged. In first 63.2%, 86.5, 95, 98.2 & 99.3% of total charge is stored ( thanks to dhanesh nair)

  4. This video is a little difficult for English only speakers to understand, but this gentleman is obviously very sharp and knows exactly how these circuits work. Watch it twice and you got it. I highly recommend this video for anyone seeking to better understand clamping circuits. Two thumbs up.

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