When the semiconductor diode is turned on, it is equivalent to the switch is closed (the circuit is connected) and when it is turned off, it is equivalent to the switch is opened (the circuit is cut off). Therefore, the diode can be used as a switch. The common model is 1N4148. Due to the unidirectional conductivity of the semiconductor diode, the PN junction is conductive under the positive bias voltage, and the resistance in the conductive state is very small, about tens to hundreds of ohms; Under the reverse bias voltage, it is in the off state, and its resistance is large. Generally, the silicon diode is in the range of 10 Μ Above Ω, the germanium tube also has tens of thousands to hundreds of thousands of ohms. Using this characteristic, the diode will play the role of controlling the current on or off in the circuit, and become an ideal electronic switch.
The above description is applicable to any ordinary diode, or the principle of the diode itself. But for switching diodes, the most important feature is the performance under high frequency conditions.
At high frequency, the barrier capacitance of the diode exhibits extremely low impedance and is connected in parallel with the diode. When the capacitance of the barrier capacitor reaches a certain level, the switching performance of the diode will be seriously affected. Under extreme conditions, the diode will be short circuited, and the high-frequency current will no longer pass through the diode, but directly bypass the barrier capacitor, and the diode will fail. However, the barrier capacitance of the switching diode is generally very small, which is equivalent to blocking the barrier capacitance, achieving the effect of maintaining good unidirectional conductivity under high frequency conditions.
