# How to use diodes to achieve output of different voltages in a microcontroller?

The unidirectional conductivity of diodes can be used to design interesting and practical circuits. Share this article to analyze how clipping circuits and clamping circuits are implemented with diodes.

The unidirectional conductivity of diodes can be used to design interesting and practical circuits. Share this article to analyze how clipping circuits and clamping circuits are implemented with diodes.

Limiter circuit

As shown in the figure below, when in the positive half cycle, and VIN is greater than or equal to 0.7V, the diode is conducting forward. At this point, VOUT is clamped at 0.7V.

When VIN is less than 0.7V, the diode is in the off state, which is equivalent to the current reverse in the negative half cycle, and the diode is also in the off state. At this time, VOUT=VIN, and the VOUT waveform changes with VIN.

Radiation Limiting Circuit Diagram

According to the principle of the radiation limiting circuit above, the following bidirectional radiation limiting circuit can be designed.

Bidirectional Radiation Limiting Circuit Diagram

However, sometimes the 0.7V voltage can not meet the requirements, so how to generate the clipping voltage of different sizes? The bias voltage VBIAS is added to the circuit, and the diode can be turned on only when VIN is greater than or equal to VBIAS. At this time, VOUT is clamped, and its value is 0.7V+VBIAS, as shown in the figure below.

Schematic diagram of bias limiting circuit

clamp circuit

The following is a clamp circuit implemented by a diode combined with a capacitor. The diode conduction drop is not considered in the analysis, assuming that the RC time constant is large enough so that the output waveform is not distorted.

Clamp Circuit Principle

When the input Vin is negative during the negative half cycle, the current is shown by the red arrow in the figure below. The diode is turned on and the capacitor is gradually charged to V, during which Vout=0.

When the input Vin is positive in the positive half cycle, the current is shown by the blue arrow. The diode is cut off, Vout is equal to the voltage on the capacitor plus the positive half-cycle voltage V, at this time Vout=2V.

Clamp Circuit Principle

Bias Clamp Circuit

Similar to the limiter circuit, in order to obtain the required clamping value, a bias voltage should be added to the circuit, as shown in the figure below.

Bias Clamp Circuit

When the applied bias voltage is consistent with the conduction direction of the diode, the clamping value will increase by V1, Vout=2V+V1.

Application example of bidirectional diode clamp circuit

In some circuits, the clamping effect of two diodes is used for protection, as shown in the figure below, assuming that 0.7V is the turn-on voltage of D1 and D2.

Vin is greater than or equal to Vmax, D1 is turned on, and Vout will be clamped at Vmax

When Vin is less than or equal to Vmin, Vout is clamped at Vmin

Diode Clamp Protection Circuit

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