Clamp Diodes: Principles, Functions, and Applications

Clamp means jamming the position. In circuit, is means controlling the voltage. Clamp Diode is a kind of diode that is used to limit the potential of a certain point in the circuit, controlling the input voltage to a peak value to a predetermined voltage, without changing the signal. The working principlealso the unidirectional conductivity of the diode.

What is the principle of clamping diodes? To understand this question, you must first understand clampping circuit. A circuit that can fix a certain part of the input and output signal waveform at a selected level is called a clamp circuit. If you want to change the clamp level, you can connect a DC potential in the circuit. If you want to clamp the bottom of the pulse, you can reverse the diode on the side. The following figure shows the input signal clamping circuit of a typical integrated operational amplifier block.

The clampping diode protection circuit is consisted of two diodes in reverse series. Only one diode can be turned on at a time, and the other is in the off state. As a result, the forward and reverse pressure drop of it will be clamped to the forward conduction of the diode. The voltage drop is below 0.5-0.7, so as to protect the circuit.

The function of the clampping circuit is to keep the top or bottom of the periodically changing waveform at a certain DC level. Take a common diode clamp circuit as example, suppose the input signal, at zero time, uO(0+)=+E, uO produces a positive transition with amplitude E. After that, between 0 and t1, the diode D is turned on, the charging current of the capacitor C is very large, and uC quickly becomes equal to E, causing uO=0. At t1, ui(t1)=0, and uO has an amplitude -E jump again. During t1~t2, D is turned off, and the charging capacitor C can only be discharged through R. Usually, the value of R is very large, causing uC drops very slowly, and uO changes very little. At t1, uI(t2) = E, and uO has a jump of the amplitude E. During t2 to t3, D is turned on and capacitor C is recharged. Unlike the period from 0 to t1, there is a large amount of charge stored on the capacitor at this time, so the charging duration is shorter, and uO decreases to zero more quickly. Repeat the above process later, the waveforms of uO and uC. It can be seen that the top of uO is basically limited to zero level, so the circuit is called a zero-level positive peak (or top) clamp circuit.

Connect the diode reversely to clamp the bottom of the input rectangular wave at zero level, forming a zero-level negative peak (or bottom) clamp circuit.

Triode clamp circuit, if its BE junction is also seen as a diode, then, in terms of the principle of clamping, the circuit shown is exactly the same, except that the circuit also has an amplifying effect.

To get to know the priciples of clamp diodes better, here are the introductions of the principles of two different ciucuits

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