A semiconductor diode is switched on equivalent to a switch closed (circuit on) and off equivalent to a switch on (circuit off), so the diode can be used as a switch, common model 1N4148. Because the semiconductor diode has the characteristics of unidirectional conduction, PN junction conduction under positive bias, in the on-state resistance is very small, about tens to hundreds of euros; In the reverse bias, the cut-off state, the resistance is very large, silicon diode in 10 MPA above, germanium tube also has tens of thousands of euros to hundreds of thousands of euros. Using this property, the diode will play a role in the circuit to control the current on or off, becoming an ideal electronic switch.
The above description, in fact, applies to any ordinary diode, or the principle of the diode itself. But for switching diodes, the most important characteristic is the performance under high frequency conditions.
At high frequencies, the barrier capacitance of the diode exhibits an extremely low impedance and is in parallel with the diode. When the barrier capacitance itself reaches a certain level, it will seriously affect the switching performance of the diode. Extreme conditions will short-circuit the diode, high-frequency current will not pass through the diode, but directly detour the barrier capacitor, diode failure. However, the barrier capacitance of the switching diode is generally very small, which is equivalent to blocking the barrier capacitance this road, to achieve the effect of maintaining good one-way conductivity under high frequency conditions.
Switching diode from cut-off (high resistance state) to conduction (low resistance state) time is called opening time; The time from conduction to cut-off is called reverse recovery time; The sum of the two times is called the switching time. Generally, the reverse recovery time is longer than the opening time, so only the reverse recovery time is given in the parameters of the switching diode. Switching diode switching speed is quite fast, like silicon switching diode reverse recovery time is only a few nanoseconds, even germanium switching diode, it is only a few hundred nanoseconds.
Switching diode has the characteristics of fast switching speed, small size, long life, high reliability, widely used in electronic equipment switching circuit, detection circuit, high frequency and pulse rectifier circuit and automatic control circuit.
Switching diode is divided into ordinary switching diode, high-speed switching diode, ultra-high-speed switching diode, low power switching diode, high reverse voltage switching diode, silicon voltage switching diode and so on.