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This article refers to what is the function and principle of diode clamping? - Know almost
The errors in some articles have been corrected, and the unclear explanations have been explained in detail. Please read the two articles together for better results.
Clamp circuit description
1. We all know that diodes have unidirectional conductivity. This characteristic of diodes can be used to rectify the circuit, which is our rectifier circuit. In addition, this feature can be used to clamp the voltage at a certain point in the circuit, which is the so-called clamping circuit.
2. The definition of clamping: It is to forcibly clamp the signal to a certain potential, raising or lowering the reference potential of the signal, but not changing the waveform of the original signal. This is clamping.
3. Circuit structure: diode D, capacitor C, resistor R
4. The clamp circuit is divided into: forward clamp and negative clamp circuit
5. When analyzing the circuit, we imagine the diode as an ideal state. The RC time constant is unlimited and large enough, and there is no waveform distortion. And all AC signals can generate clamping function
6. Taking advantage of the unidirectional conductivity of the diode, when the cathode of the diode is grounded, and the potential of the positive terminal circuit is higher than the ground, the diode will conduct and pull its potential down, that is, the positive terminal circuit is clamped to zero potential or below. (Ignore tube pressure drop).
7. Taking advantage of the unidirectional conductivity of the diode, when the anode of the diode is grounded, when the potential of the negative terminal circuit is higher than the ground, the diode will cut off, and its potential will not be affected by the diode in any way.
8. Diode clamping takes advantage of the unidirectional conductivity of the diode, that is, when the negative electrode voltage of the diode is greater than the positive electrode, the diode is turned off, and when the anode voltage is greater than the negative electrode, the diode is turned on.
How the clamp circuit works
Diode clamping takes advantage of the unidirectional conductivity of the diode. That is, when the negative electrode voltage of the diode is greater than the anode electrode, the diode is turned off. When the anode voltage is greater than the cathode electrode and is turned on, the voltage across the diode is limited to its tube voltage drop. The silicon tube is about 0.7V, which means that the voltage across the diode is clamped at 0.7V. If the cathode of the diode is connected to 5V, then the anode voltage is 5V+0.7=5.7V. If the anode of the diode is connected to 5V, then the cathode voltage is 5V-0.7V=4.3V.
Classic circuit applications
Diodes D1 and D2 also play a clamping role. When the input signal is greater than 3.3V, diode D1 conducts and clamps the input voltage at 3.3V+0.7V=4V. When the input signal is less than -3.3V, diode D21 turns on and clamps the input voltage at -3.3V-0.7V=-4V. This clamps the input signal to a certain range from +4V to -4V. After reaching the protection level circuit.
This circuit is a little difficult to understand. My understanding is as follows:
First, Vout is equivalent to the voltage of a parallel load, and then the actual current flow should be from Vcc to Vdd . Based on this condition, we will look at the following three situations.
1. When Vin is greater than or equal to 0.7V, then it is obvious that D1 is conductive, so there is current flowing through it. Then we require that the current flow direction is from Vcc to Vdd, then D2 should at least be conductive, so there can be no reverse direction. The voltage is applied to D2, so Vout is clamped at 0.7V at this time.
2. Similarly, when Vin is less than or equal to -0.7V, Vout is clamped at -0.7V to ensure that there is no reverse voltage on D1.
3. When Vin is less than 0.7V and greater than -0.7V, it meets the requirements.
(The above are all personal understandings, if there are any errors, please point them out)
