A semiconductor diode is equivalent to a closed switch (circuit connected) when it is turned on, and an open switch (circuit cut off) when it is cut off, so a diode can be used as a switch, and the common model is 1N4148. Because of the unidirectional conduction characteristic of the semiconductor diode, the PN junction is turned on under positive bias, and the resistance in the on state is very small, ranging from tens to hundreds of ohms; under reverse bias, it is in the cut-off state, and its resistance is very large. Generally, silicon diodes are above 10MΩ, and germanium tubes also have tens of kilohms to hundreds of kilohms. Using this characteristic, the diode will play a role in controlling the current on or off in the circuit, becoming an ideal electronic switch. The above description actually applies to any ordinary diode or the principle of the diode itself. But for switching diodes, the important feature is their performance under high-frequency conditions. Under high-frequency conditions, the barrier capacitance of the diode exhibits a very low impedance and is parallel to the diode. When this barrier capacitance itself reaches a certain level, it will seriously affect the switching performance of the diode. Under extreme conditions, it will short-circuit the diode, and the high-frequency current will no longer pass through the diode, but directly bypass the barrier capacitance, and the diode will fail. The barrier capacitance of switching diodes is generally very small, which is equivalent to blocking this path, achieving the effect of maintaining good unidirectional conduction under high-frequency conditions.

Switching diode circuit analysis

Switching diodes are also PN junction structures like ordinary diodes, but they require better-switching characteristics for these diodes. When a positive voltage is applied to the switching diode, the diode is in an on state, which is equivalent to the on state of the switch; when a reverse voltage is applied to the switching diode, the diode is in a cut-off state, which is equivalent to the off state of the switch. The on-and-off states of the diode complete the function of opening and closing. Switching diodes use this characteristic and through the manufacturing process, they have better-switching characteristics, that is, faster switching speed, smaller junction capacitance, smaller internal resistance when turned on, and very large resistance when cut off.