What are clamp diodes?
Clamping refers to a measure that limits the potential of a certain point to a prescribed potential, and is an overvoltage protection technology. The circuits that produce this action are called clamping circuits. The function of the clamp circuit is to keep the top or bottom of the periodically changing waveform at a certain DC level. Thereby improving the working stability of the whole circuit. There is a clamping diode in the clamping circuit. The clamping diode generates a clamping voltage.
High-precision operational amplifiers allow system designers to condition the signal (amplify, filter, and buffer) while maintaining the accuracy of the original signal. When the information is contained in a signal with very small fluctuations, it is extremely necessary for the operational amplifier on the signal path to have very low DC and AC error performance during operation. The overall system accuracy depends on the accuracy of the signal path. In some applications, it may appear that a voltage other than the supply voltage drives the input of the op amp—this situation is called an overvoltage condition. Long-term (or even short-term) excessive input current—if the current is high enough—may damage the op amp. Faced with this possibility, system designers usually add an overvoltage protection (OVP) circuit to the amplifier input. Therefore, it is difficult to introduce the OVP circuit without increasing the error (loss of system accuracy).
Clamping, is a classic overvoltage protection technology.
The diagram shown is a common method of OVP (overvoltage protection). When the amplitude of the input signal (VIN) exceeds one of the power supply voltages plus the forward voltage of the diode, the diode (DOVPP or DVPN) will be forward biased and current will flow to the power rail. Excessive current may damage the op amp. In this application, we used the ADA4077, a highly accurate operational amplifier with a maximum power supply range of 30V (or ±15V). The clamping diodes are 1N5177 Schottky diodes, because their forward conduction voltage is equal to about 0.4V, which is lower than the forward conduction voltage of the op amp input electrostatic discharge (ESD) protection diode; therefore, the clamping diode will be before the ESD diode Start to conduct current. The overvoltage protection resistor ROVP limits the forward current flowing through the clamping diode, keeping it below the maximum current rating, and preventing damage from excessive current. The feedback loop resistor RFB is used because any input bias current on the non-inverting input will flow through the ROVP and produce an input voltage error-increasing the RFB value can eliminate the error because it will produce a similar voltage at the inverting input.