The usage of a switching diode, why a diode can be used as a switch

In fact, the diode also has a very special performance, that is, it can be used as a temperature detection device very well, stable, reliable, convenient and very cheap. Many people may not know that it can be used in this way.

The principle is very simple: the PN junction of the diode has negative temperature characteristics, and its positive voltage drop decreases by about 3mV for every degree C increase in temperature. If five 1N4148 diodes are connected in series, there is a change of 15mV degree C.

For op amps with LM358 and LM324 or LM339, a change of 2MV is enough to flip the output. In specific use, as long as a resistor and the diode are connected in series, the resistor plays the role of current limiting, so that the forward current of the diode is between 3mA. Take the forward voltage from both ends of the diode and give it to the comparator input.

In the early years, I used this thing to replace the temperature sensor resistor in Toshiba refrigerators that was easily damaged, and so far none of them have a temperature runaway problem, and the people in Toshiba's maintenance department are also dizzy and never understand the mystery.

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 the PN junction of the diode has a negative temperature characteristic, the positive voltage 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.

Switching diodes and ordinary diodes are both PN junctions, the difference is that the junction capacitance of switching diodes is small and the response speed is fast. Ordinary diodes can also be used as switching circuits, the diode has very little resistance under the action of forward voltage, and is in the on-state state, which is equivalent to a switch-on; Under the action of the reverse voltage, the resistance is very large, and it is in a cut-off state, like an open switch. Using the switching characteristics of diodes, various logic circuits can be composed.

It plays the role of opening and closing, and is mostly used in oscillating circuits.

A switching diode is actually a high-current high-frequency tube.

This is due to the fact that semiconductor diodes have the property of unidirectional conductivity.

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 silicon diodes are more than 10m, and germanium tubes also have tens of thousands of ohms to hundreds of kiloohms. 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.

Semiconductor diode structure

A semiconductor diode is formed by an electrode at each end of the p-n junction and a tube shell. The electrode that emerges from one end of the p-type semiconductor of the p-n junction is called the anode, and the electrode that emerges from the n-type semiconductor end of the p-junction is called the cathode. Semiconductor diodes can be divided into point contact type, surface contact type and planar type according to different structures.

The point-contact semiconductor diode is made of a metal wire in contact with the surface of the semiconductor, and through a special process, a PN junction is formed on the contact point, a lead wire is made, and the tube shell is packaged. The point contact diode has a small PN junction area and good high-frequency performance, making it suitable for high-frequency detection circuits and switching circuits.

The PN junction of the surface contact semiconductor diode is made by the alloy process. Surface-contact diodes have a large PN junction area and can pass large currents, and are generally used in low-frequency rectifier circuits.

The switch cannot be unilateral, it must reach the distribution capacitor to act as coupling saturation in the circuit, so that its current is saturated and there is no longer the flow of current. In the electrogenic part of the DC appliance, a diode of sufficient power can be connected in series to protect the positive and negative electrodes of the electric wish, so that no current will pass through. This can be said to be a switch effect!

The resistance of the diode is very small under the action of forward voltage, and it is in the conduction state, which is equivalent to a switch-on; Under the action of the reverse voltage, the resistance is very large, and it is in a cut-off state, like an open switch.

1. Diode, (English: diode), among electronic components, a device with two electrodes, only allows current to flow in a single direction, and many are used to apply its rectification function. Varactor diodes (VAFIC diodes) are used as electronic tunable capacitors.

2. The current directivity of most diodes is usually called "rectifying" function. The most common function of a diode is to allow only current to pass through a single direction (known as forward bias) and to block it in reverse direction (known as reverse bias). Therefore, the diode can be thought of as an electronic version of the check valve.

First, the nature is different.

1. Switching diodes.

Properties: A type of semiconductor diode, which is made to be carried out on the circuit"On"、"off"The specially designed and manufactured type of diode is a type of diode.

2. Rectifier diode.

Properties: One will alternate current.

A semiconductor device that can be converted into direct current energy.

Second, the characteristics are different.

1. Characteristics of switching diode: the time from cut-off (high-resistance state) to on-conducting (low-resistance state) of the switching diode is called the opening time; The time from turn-on to cut-off is called the reverse recovery time; The sum of the two is called the switching time. In general, the reverse recovery time is greater than the turn-on time, so only the reverse recovery time is given in the switching diode usage parameters.

The switching speed of a switching diode is quite fast. For example, a silicon switching diode has a reverse recovery time of only a few nanoseconds.

Even germanium switching diodes are only a few hundred nanoseconds.

2. Rectifier diode characteristics: using PN junction.

The unidirectional conductivity of the alternating current turns the alternating current into a pulsating direct current. The rectifier diode has a large leakage current, and most of the rectifier diodes are sealed with surface contact materials. The shape of the rectifier diode is shown in Figure 1.

In addition, the parameters of the rectifier diode include the maximum rectifier current, which refers to the maximum current that the rectifier diode can pass through for a long time. It is the main parameter of the rectifier diode and the main basis for the selection of the rectifier diode.

The high-frequency performance of the switching diode is good, and it is mainly used for the switching circuit as an electronic switch, while the rectifier tube is generally not very high-frequency performance (the high-frequency performance of the rectifier tube in the switching power supply is also very good), and it is mainly used for the rectification of the power frequency current. It usually operates at high voltages and high currents.

Switching diodes:

1. The switching speed of the switching diode is high, that is, the application frequency is high.

2. The switching diode has good high-frequency performance and is mainly used as an electronic switch in the switching circuit.

Rectifier Diode:

1. Rectifier diodes are used in the field of power frequency and high current.

2. The general high-frequency performance of the rectifier tube is not very good (the high-frequency performance of the rectifier tube in the switching power supply is also very good), which is mainly used for rectifying the power frequency current. It usually operates at high voltages and high currents.

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. It takes less time than the general diode to change from on-to cut-off or from cut-off to on, and the common ones are 2AK, 2DK and other series, which are mainly used in electronic computers, pulse and switching circuits.

A rectifier diode is a semiconductor device used to convert alternating current into direct current.

The positive connection of the diode is that the positive potential is connected to the positive pole of the diode, and the negative potential is connected to the negative pole of the diode. That is, in the circuit principle, the positive pole of the diode is in the absence of high electric rolling and the negative electrode is in the low potential, which is the positive connection of the diode.

The diode has a limit to the forward maximum current; There is a maximum limit on the reverse voltage; Today's diodes are basically found in rectifier circuits and integrated circuits.

Electrical conductivity: The most important characteristic of a diode is its unidirectional conductivity. In an ascending 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 terminal is connected to the low potential end, and the diode will be turned on, and this connection method is called forward bias. It must be noted that when the forward voltage applied to both ends of the diode is very small, the diode still cannot be conducted, and the forward current flowing through the diode is very weak.

Only when the forward voltage reaches a certain value (this value is called "threshold voltage", also known as "dead zone voltage", germanium tube is about, silicon tube is about that), the diode can really be turned on. The voltage across the diode remains essentially the same after turn-on (about germanium tubes, about silicon tubes, and is called the "forward voltage drop" of the diode). <

<> 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.