# How to use diodes to achieve different voltage output in a single chip microcomputer? 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.

The unidirectional conductivity of diodes can be used to design interesting and practical circuits.

Limiter circuit

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

When VIN is less than 0.7V, the diode is in the cut-off state. In the negative half cycle, the current is reversed and the diode is also in the cut-off state. At this time, VOUT=VIN, and the VOUT waveform changes with VIN. Schematic diagram of limiter circuit

According to the principle of the above limit limit circuit, the following two-way limit limit circuit can be designed. Schematic diagram of bidirectional limiter circuit

However, sometimes the 0.7V voltage cannot meet the requirements, so how to generate different amplitude limiting voltages?

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 conduction voltage drop of the diode is not considered in the analysis, and it is assumed that the RC time constant is large enough so that the output waveform will not be distorted.

Principle of Clamping Circuit

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 off, and Vout is equal to the voltage on the capacitor plus the positive half-cycle voltage V, at this time Vout=2V. Principle of Clamping Circuit

Bias clamp circuit

Similar to the limiter circuit, in order to obtain the required clamp 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 diode conduction direction, the clamp value will increase by V1, Vout=2V+V1.

Application examples of bidirectional diode clamp circuit

In some circuits, the clamping effect of two diodes is used for protection. As shown in the figure below, suppose 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