In some important applications of diodes, devices often change alternately between high resistance and low resistance at high speed. In these applications, some voltage waveforms in the circuit are in the form of pulses, that is, square waves that vary between a high level (usually 5v) and a low level (usually 0V). The switching frequency of these high and low voltage signals is very high, which makes the diode switch between "on" and "off" at high speed. Connect a resistor to the silicon diode. When the power supply voltage changes alternately from 0V and 5v, the current at both ends of the resistor also changes alternately. When e (z)=5v, the diode is in a forward bias state, and it is in a conducting state. The nail current flows through the resistor, and the voltage across the resistor is equal to 5-0.7 = 4.3V. When e(j)=0V, the diode is in a high resistance state, that is, in an off state. Because no current flows through the resistor, the voltage across the resistor is equal to zero. This mode is very similar to the function of rectifier. These are two extreme states in digital circuits-high level and low level. In other words, it is assumed that the combined voltage value is in one of these two states. Because the role of diodes in these circuits is to turn on or off at different voltage levels, this application is also called switching circuit.

A typical diode switching circuit includes two or more diodes, each connected to an independent voltage source. To correctly understand the working process of the switching circuit, we must first determine which voltage source determines each diode, which is in the on state and which is in the off state. The key to correctly distinguish which state it is in is that if the anode potential of the diode is positive relative to the cathode potential, it is in a positive bias state, that is, when the anode potential of the diode (relative to the ground) is higher than the cathode potential (relative to the ground), it is in a positive bias state. Of course, it can also be said that the cathode potential of the diode is (relatively) lower than the anode potential (relatively). On the contrary, if you want the diode to be in a reverse bias state, let the anode of the diode be negative relative to the cathode potential, which is equivalent to the cathode of the diode being positive relative to the anode.