Switching diode — SUNMATE

working principle

When the semiconductor diode is turned on, it is equivalent to the switch closing (circuit on) and when it is turned off, it is equivalent to the switch opening (circuit off). Therefore, the diode can be used as a switch. The common model is 1N4148. Due to the unidirectional conductivity of semiconductor diodes, the PN junction is turned on under positive bias voltage, and the resistance in the on state is very small, about tens to hundreds of ohms; Under the reverse bias voltage, it is in the cut-off state, and its resistance is very large. Generally, the resistance of silicon diode is 10 Μ Ω or more, germanium tubes also have tens to hundreds of kiloohms. Using this characteristic, the diode will control the current on or off in the circuit, and become an ideal electronic switch.

The above description is actually applicable to any ordinary diode, or the principle of the diode itself. But for switching diodes, the most important feature is the performance at high frequency.

At high frequency, the barrier capacitance of the diode shows very low impedance and is connected in parallel with the diode. When the capacitance of the barrier capacitor reaches a certain level, it will seriously affect the switching performance of the diode. Under extreme conditions, the diode will be short circuited, the high-frequency current will no longer pass through the diode, but directly bypass the barrier capacitor, and the diode will fail. The barrier capacitance of switching diode is generally very small, which is equivalent to blocking the path of barrier capacitance, which can maintain good unidirectional conductivity at high frequency. [1]

Working characteristics

The time of switching diode from off (high resistance state) to on (low resistance state) is called on time; The time from conduction to deadline is called reverse recovery time; The sum of the two times is called the switching time. Generally, the reverse recovery time is greater than the on time, so only the reverse recovery time is given in the service parameters of the switching diode. The switching speed of switching diodes is quite fast. For example, the reverse recovery time of silicon switching diodes is only a few nanoseconds, and even germanium switching diodes are only a few hundred nanoseconds.

Switching diode has the characteristics of fast switching speed, small volume, long service life and high reliability. It is widely used in switching circuit, detection circuit, high frequency and pulse rectification circuit and automatic control circuit of electronic equipment.

type

Switching diodes are divided into ordinary switching diodes, high-speed switching diodes, ultra-high-speed switching diodes, low-power switching diodes, high back voltage switching diodes, silicon voltage switching diodes and so on.

Common switching diode

Common domestic common switching diodes include 2ak series germanium switching diodes. Table 4-8 shows the main parameters of 2ak series switching diodes.

High speed switching diode

Compared with ordinary switching diodes, high-speed switching diodes have shorter reverse recovery time and faster on and off frequency.

The commonly used domestic high-speed switching diodes are 2ck series.

Imported high-speed switching diodes include 1n series, 1s series, 1SS series (with lead plastic packaging) and RLS series (surface mounting).

Ultra high speed switching diode

The common ultra-high speed switching diodes are 1SS series (with lead plastic packaging) and RLS series (surface packaging).

Low power switching diode

The power consumption of low-power switching diode is lower, but its zero bias capacitance and reverse recovery time are lower than those of high-speed switching diode.

The commonly used low-power switching diodes are RLS series (surface package) and 1SS series (lead plastic package).

High back voltage switching diode

The reverse breakdown voltage of high back voltage switching diodes is above 220V, but its zero bias capacitance and reverse recovery time are relatively large.

The common high back voltage switching diodes are RLS series (surface package) and 1SS series (lead plastic package).

Silicon voltage switching diode

Silicon voltage switching diode is a new type of semiconductor device, which can be divided into unidirectional voltage switching diode and bidirectional voltage switching diode. It is mainly used in trigger, overvoltage protection circuit, pulse generator, high voltage output, time delay, electronic switch and so on.

Unidirectional voltage switching diode, also known as turning diode, is composed of silicon semiconductor material with pnpn four-layer structure. Its positive is negative resistance switching characteristic (it means that when the applied voltage rises to the positive turning voltage value, the switching diode changes from off state to on state, that is, from high resistance to low resistance), and the reverse is stable characteristic. Bidirectional voltage diode is composed of silicon semiconductor material with NPN five layer structure. Its forward and reverse have the same negative resistance switching characteristics.

Diode (English: Diode), a device with two electrodes in electronic components, which only allows current to flow in a single direction. Many uses are its rectification function. The varactor diode is used as an electronic adjustable capacitor. The current directivity of most diodes is usually called "rectifying". The most common function of diodes is to allow current to pass only in a single direction (called forward bias) and block in reverse (called reverse bias). Therefore, the diode can be thought of as an electronic check valve.

Early vacuum electronic diode; It is an electronic device that can conduct current in one direction. There is a PN junction and two lead terminals inside the semiconductor diode. This electronic device has the conductivity of unidirectional current according to the direction of applied voltage. Generally speaking, crystal diode is a p-n junction interface formed by sintering p-type semiconductor and n-type semiconductor. A space charge layer is formed on both sides of the interface to form a self built electric field. When the applied voltage is equal to zero, the diffusion current caused by the carrier concentration difference on both sides of the p-n junction is equal to the drift current caused by the self built electric field, which is also the diode characteristic under normal conditions.

Early diodes included "cat's whisker" crystals "and vacuum tubes (called" thermal valves "in the UK). Nowadays, most of the most common diodes use semiconductor materials, such as silicon or germanium.