The switching principle of the diode, the role of the switching diode

For example, a child is short and wants to go out but can't reach the deadbolt and can't open the door, and an adult is tall enough to reach the deadbolt, and the child can enter and exit after he opens the door.

The diode is equivalent to the door above, it has a certain opening voltage (also called on-voltage, threshold voltage, equivalent to the deadbolt), the small signal that does not reach the opening voltage can not pass through it, and the switching signal that controls whether the diode is turned on or not is equivalent to the adult above, its voltage is higher than the opening voltage of the diode, and when the switch control signal is added to the diode, the diode is turned on, and then the small signal can pass through the diode.

The switching signal is generally a DC voltage signal, and the small signal to be controlled is generally an AC signal.

The diode does not have the function of switching, and the triode does, which control the collector and emitter of the triode through the base current of the triode to make it in a saturation conduction and cut-off state.

The diode characteristics are forward conduction and reverse shut-off. There is a voltage drop (about volts) in the forward conduction, and the forward resistance is small, and the reverse resistance is large. There is a ...... of withstand voltage parameters in reverse

The principle is the same as that of ordinary diodes, (pn junction, unidirectional conduction).The switching speed is fast (high frequency) and the junction capacitance is small.

The 1N4148 is a typical example of a small signal switching diode.

The voltage drop of this diode is relatively large, so that the signal amplitude is greater than the voltage drop of the tube.

The role of switching diodes for people who are not familiar with electrical knowledge, and do not know what the diode is, the switching diode plays a great role in the circuit, the following I have collected some relevant information about the role of the switching diode, I hope it can help you!

1. It is used as a switching circuit. In the on-state state, the resistance of the diode under the action of forward voltage is very small, which is equivalent to a switch-on; In the cut-off state, the resistance is large, like an open switch. With this characteristic, various logic circuits can be composed.

2. As a temperature detection device. Because of the pn junction of the diode.

It has negative temperature characteristics, and its positive pressure drop decreases by about 3mV for every degree C increase in temperature. As long as a resistor and diode are connected in series, the resistor acts as a current limiter, and the temperature of the appliance can be detected.

Uses of switching diodes:

In addition to meeting the requirements of ordinary diodes and performance indicators, switching diodes also have good high-frequency switching characteristics (short reverse recovery time), and are widely used in home appliances, computers, televisions, communication equipment, household audio, DVD players, instrumentation, control circuits and various high-frequency circuits.

Classification of switching diodes:

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

1. Switching diode concept

A switching diode is a type of semiconductor diode that is designed to be carried out on an electrical circuit"On"、"off"A type of diode that is specially designed and manufactured.

2. The role of switching diodes

In fact, to put it simply, it plays "on" and "off" in the circuit'Function. So how is this role achieved? Since the on-resistance of the semiconductor diode is very small under the forward bias voltage, and when the reverse bias cut-off is applied, the one-way conductivity of the semiconductor diode can be used to turn the current on and off in the switching circuit.

3. The parameters required when selecting the specific model

When selecting a switching diode, the main parameters that need to be paid attention to are: forward current, maximum response voltage, reverse recovery time, etc.

4. How to choose a switch diode

The medium-speed switching current and detection circuit can be selected with 2AK series ordinary switching diodes. High-speed switching diodes of the RLS series, ISS series, 1N series and 2CK series can be selected for high-speed switching circuits.

5. The main application of switching diodes

Switching diodes are mainly used in radios.

Household appliances and electronic equipment such as televisions and DVD players have switching circuits, detection circuits, high-frequency pulse rectifier circuits, etc.

1. The most important feature of the switching diode is its performance under high-frequency conditions. At high frequencies, the diode's barrier capacitance exhibits extremely low impedance and is connected in parallel with the diode. When the capacitance of this barrier capacitor itself reaches a certain level, it will seriously affect the switching performance of the diode.

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. The barrier capacitance of the switching diode is generally very small, which is equivalent to blocking the path of the barrier capacitor and achieving the effect of maintaining good unidirectional conductivity under high-frequency conditions.

2. When the semiconductor diode is turned on, it is equivalent to the switch closing (circuit on), and when it is cut-off, it is equivalent to the switch opening (circuit cutting), so the diode can be used as a switch, and the commonly used model is 1N4148. Due to the unidirectional conductivity of the semiconductor diode, the PN junction is turned on under the positive bias voltage, and the resistance in the conduction state is very small, about tens to hundreds of ohms; Under the reverse bias, it is in a cut-off state, and its resistance is very large, generally the silicon diode is more than 10, and the germanium tube also has tens of thousand ohms to hundreds of thousand ohms. With this feature, the diode will play a role in controlling the current on or off in the circuit, making it an ideal electronic switch.

The above description actually applies to any ordinary diode, or the principle of the diode itself.

<> the commonly used switching components in digital circuits are mainly known as follows:

1. Triode, the full name should be semiconductor transistor, also known as bipolar transistor, transistor, is a semiconductor device that controls the current, and its function is to amplify the weak signal into an electrical signal with a large amplitude value, and is also used as a contactless switch. Crystal transistor is one of the basic components of semiconductors, which has the effect of current amplification and is the core component of electronic circuits;

2. Lu Sui diode, a device with two electrodes, only allows the current to flow in a single direction, and many of the use deficit sections are applied to its rectification function. Varactor diodes, on the other hand, are used as electronic tunable capacitors. The most common function of diodes is to allow only current to pass through a single direction, so they can be used as switching elements;

In the digital circuit, there are only two levels of high and low, generally the high level of the bridge is 5, representing "1", and the low level is 0, representing "0", and as the requirements of the switching diode in the digital circuit: working under the pulse circuit, the signal is the two levels of high and low voltage, requiring the diode to work at a high frequency, fast speed, and steep performance on the front and back edges, and the high-brightness Sun level diode is applied at both ends of the diode to be turned on, and the low level is not conducted. This is the switching diode element, such as the commonly used 1N4148 and other two-finch-key mammode.

A diode, a device with two electrodes that allows current to flow in a single direction, is used in many electronic components to apply its rectification function. and varactor diodes (varicaps

diode) is used as an electronic tunable capacitor. The current directivity of most diodes is often referred to as "rectifying". The most common function of a diode is to allow only current to pass through a single direction (known as forward bias) and block it in reverse.

This is called reverse bias). Therefore, the diode can be thought of as an electronic version of the check valve.

a) VD cut-off, UO=3V.

Process: Assuming VD cut-off, the cathode is 6V, the anode is 3V, and the diode is subjected to a reverse voltage, cut-off. Output voltage UO = 3V.

b) VD1 cut-off, VD2 on, assuming VD1, VD2 is the ideal diode, then the output voltage UO=0V

Procedure: Assuming VD1, VD2 cut-off, then VD1 cathode 6V, anode -12V, back pressure, cut-off. VD2 anode 0V, cathode -12V, forward voltage on, assuming that the diode management, no voltage drop, then the cathode is 0V, VD1 is still subjected to back pressure, maintain the cut-off state.

The final output voltage is short-circuited by VD2 and the output is 0V.

c) VD1 is turned on, VD2 is cut-off, and the output voltage UO=-3V is assumed to be managed by the diode.

Process: Assuming VD1 and VD2 cut-off, then VD1 cathode -3V, anode +12V, conduction, its anode is embedded at -3V, so VD2 anode -3V, cathode 0V, backpressure cut-off. Output voltage UO = 3V.

The working principle of the diode: the crystal diode is a p-n junction formed by a p-type semiconductor and an n-type semiconductor, which forms a space charge layer on both sides of the interface of its cavity and failure, and has a self-built electric field.

When there is no applied voltage, the diffusion current caused by the difference in carrier concentration on both sides of the p-n junction and the drift current caused by the self-built electric field are equal. When there is a forward voltage bias in the external area, the mutual suppression effect of the external electric field and the self-built electric field increases the diffusion current of the carriers and causes the forward current.

When there is a reverse voltage bias in the outside world, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current i0 that is independent of the reverse bias voltage value within a certain reverse voltage range.

The most important characteristic of diodes is their unidirectional conductivity. In a circuit, current can only flow in from the positive pole of the diode and out from the negative pole. In electronic circuits, the positive pole of the diode is connected to the high potential end, and the negative pole is connected to the low potential end, and the diode will be turned on, which is called forward bias.

In electronic circuits, the positive pole of the diode is connected to the low potential end, and the negative terminal is connected to the high potential end, at this time there is almost no current flowing through the diode, and the diode is in a cut-off state at this time, this connection method is called reverse bias.

The main parameters of the diode

1. Rated forward working current: refers to the maximum forward current value allowed to pass through the diode when it works continuously for a long time. When the current passes through the tube, the die heats up, and when the temperature exceeds the allowable limit (about 140 for silicon tubes and about 90 for germanium tubes), the die will overheat and be damaged.

Therefore, the diode should not exceed the rated forward dry section working current value of the diode.

2. Maximum reverse working voltage: When the reverse voltage added to both ends of the diode reaches a certain value, the tube will break down and lose the unidirectional conductivity. In order to ensure safe use, the maximum reverse operating voltage value is specified.

For example, the reverse withstand voltage of the IN4001 diode is 50V, and the reverse withstand voltage of the In4007 is 1000V.

3. Reverse current: refers to the reverse current of the diode flowing through the diode under the action of the specified temperature and the maximum reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the tube.