8 Common Uses of Diodes

btty038

8 Common Uses of Diodes [Copy link]

 

There was a previous version with 7 uses

Diodes are very commonly used basic components. This article mainly introduces some functions of diodes, such as anti-reverse, rectification, voltage regulation, freewheeling, detection, voltage doubling, clamping, and envelope detection.
1. Anti-reverse
In the main circuit, a diode is connected in series to utilize the unidirectional conductive characteristics of the diode to achieve the simplest, most reliable, and low-cost anti-reverse connection circuit. This low-cost solution is generally used in small current situations, such as small toys.
Because the diode will have a 0.7V (silicon tube) conduction voltage drop when it is turned on, if the actual current is very large, then a heat loss will be generated, which will cause heating. Moreover, if the reverse voltage is very large, it will exceed the reverse cut-off voltage and will also break down the diode itself, causing the diode to fail and fail to play the role of anti-reverse connection, thereby failing to protect the subsequent circuit.

2. Rectification
The function of the rectifier circuit is to convert the low-voltage AC output of the AC step-down circuit into unidirectional pulsating DC. This is the rectification process of AC. The rectifier circuit is mainly composed of rectifier diodes. The voltage after the rectifier circuit is no longer an AC voltage, but a mixed voltage containing DC voltage and AC voltage, which is usually called a unidirectional pulsating DC voltage.

3. Voltage stabilization
The diode with voltage stabilization function is called Zener diode, also known as Zener diode. By using the reverse breakdown state of PN junction, its current can vary in a wide range while the voltage remains basically unchanged. Its basic circuit structure is shown in the figure below.

4. Freewheeling
The freewheeling diode is connected in parallel at both ends of the coil (inductive component). When the current passes through the coil, an induced electromotive force will be generated at both ends. When the current disappears, the induced electromotive force will generate a reverse voltage on the components in the circuit. When the reverse voltage is higher than the reverse breakdown voltage of the component, it will damage the components such as transistors.
The freewheeling diode is connected in parallel at both ends of the line. When the current flowing through the coil disappears, the induced electromotive force generated by the coil is consumed by the circuit formed by the diode and the coil, protecting the safety of other components in the circuit.

Or the freewheeling diode in the BUCK chip circuit.

5. Detection
The peak detection circuit detects the maximum value of the input signal amplitude. Its working principle is: when the input voltage amplitude is greater than the forward voltage of the diode, the diode is turned on, the output voltage is applied to the capacitor C1, and the capacitor is fully charged. When the input voltage amplitude is lower than the previous input voltage amplitude, the diode is in a reverse bias cutoff state. At this time, the voltage across the capacitor remains basically unchanged; if the signal is input again, the input voltage amplitude must be higher than the voltage across the capacitor at this time (that is, the forward voltage applied to the diode) for the diode to be turned on.

6. Voltage doubling
The following figure is a schematic diagram of a 2-voltage doubling circuit. Its working process can be roughly analyzed as follows:
During the negative half cycle of the power supply, diode D1 is turned on and D2 is turned off. The current flows out from the lower end of the power supply through D1 and C1 and returns to the power supply. Therefore, capacitor C1 is positive on the right and negative on the left, as shown by the red arrow in the figure below. During the positive half cycle of the power supply, the voltage on capacitor C1 is superimposed on the power supply voltage, so that diode D2 is turned on and diode D1 is turned off. Capacitor C2 is positive on the top and negative on the bottom. The peak voltage can reach 2 times the peak voltage of the power supply, that is, double voltage is achieved.
The current flow during this half cycle is shown by the orange arrow in the figure below:

7. Voltage clamping
In some ADC detection circuits, two diodes are used for clamping protection. The principle is very simple. 0.7V is the conduction voltage drop of D1 and D2. When the voltage of Vin is greater than or equal to 3.3V+0.7V, D35 is turned on and Vout will be clamped at 4V; when Vin is less than or equal to -0.7V, Vout will be clamped at around -0.7V.

8. Envelope detection
The circuit structure is shown below. The key point of the design is that the RC time constant must be much larger than the carrier frequency period and much smaller than the modulation signal period.

乐在其中1100

Happy Mid-Autumn Festival! Thank you for the popular science,,,,,

btty038

Enjoy it 1100 Posted on 2022-9-10 10:09 Happy Mid-Autumn Festival! Thank you for the popular science,,,,,

Happy Mid-Autumn Festival

xiaosong06

Thanks for sharing, happy Mid-Autumn Festival

bigbat

Thank you. I have used anti-reverse, voltage stabilization, clamping and freewheeling, but have not used the others independently.

btty038

bigbat posted on 2022-9-10 16:00 Thank you very much. I have used anti-reverse, voltage stabilization, clamping, and freewheeling, but have not used the others independently.

The scenarios are different, and the application methods will be inconsistent. Some are really different environments, which is already amazing.

btty038

xiaosong06 posted on 2022-9-10 11:31 Thanks for sharing, happy Mid-Autumn Festival

Happy Double Festival. Wishing you a happy holiday with a grateful heart.

tianmeimei

The functions of a diode are:

1. Rectification: By using the unidirectional conductivity of the diode, the alternating alternating current can be converted into a single-direction pulsed direct current.
2. Switching: Under the action of the forward voltage, the resistance of the diode is very small and it is in the on state, which is equivalent to a switched on switch; under the action of the reverse voltage, the resistance is very large and it is in the off state, like a switched off switch. Using the switching characteristics of the diode, various logic circuits can be formed.
3. Limiting: After the diode is forward-conducted, its forward voltage drop remains basically unchanged (0.7V for silicon tubes and 0.3V for germanium tubes). Using this characteristic, it can be used as a limiting element in the circuit to limit the signal amplitude to a certain range.

4. Freewheeling: It plays a freewheeling role in the inductance of the switching power supply and inductive loads such as relays.

5. Detection: It plays the role of detection in the radio.

6. Variable capacitance: used in the high-frequency head of the television.

7. Display: used on displays of VCD, DVD, calculator, etc.

8. Voltage regulation: The voltage regulator diode is essentially a junction silicon diode, and the voltage regulator diode works in the reverse breakdown state. The manufacturing process of the diode makes it have a low-voltage breakdown characteristic. The reverse breakdown voltage of the voltage regulator diode is constant. A current limiting resistor is connected in series in the voltage regulation circuit so that the current after the voltage regulator tube breaks down does not exceed the allowable value. Therefore, the breakdown state can last for a long time without damage.

9. Trigger: The trigger diode, also known as the bidirectional trigger diode (DIAC), is a three-layer structure and a symmetrical two-terminal semiconductor device. It is often used to trigger bidirectional thyristors and for overvoltage protection in circuits.

gaon

Happy Mid-Autumn Festival! Thank you for popularizing science,,,,, Happy Mid-Autumn Festival! Thank you for popularizing science,,,,,

吾妻思萌

In fact, the diode is used to construct the most basic logic circuit. If it is above 0.7V, it is 1, and if it is below 0.7V, it is 0. It is simply a magical tool.

秦天qintian0303

Happy Mid-Autumn Festival, thanks for sharing!

btty038

Qintianqintian0303 posted on 2022-9-12 14:33 Happy Mid-Autumn Festival, thank you for sharing!

Happy Mid-Autumn Festival and Happy Unblocking!

se7ens

To add, is there also a lighting function?

btty038

se7ens posted on 2022-9-12 22:55 To add, does it also have a lighting function?

This is called the darkest place under the lamp, which triggers the blind spot of knowledge.

damiaa

10. Make a simple OR gate circuit.

Thank you for sharing.

baopodao

Used for infrared emission, can be used for detection, and can also be used for communication.

btty038

baopodao posted on 2022-9-14 10:20 It is used for infrared emission, which can be used for detection and communication.

Remote control that we use every day

Honghuzaitian

I learned a lot of knowledge that I didn't know before. I usually only use distillation voltage stabilization and have never used detection circuits.

476700838

baopodao posted on 2022-9-14 10:20 It is used for infrared emission, which can be used for detection and communication.

Infrared emitting tube (IR LED) is also called infrared emitting diode, which belongs to the diode category. It is a light-emitting device that can directly convert electrical energy into near-infrared light (invisible light) and radiate it.

btty038

476700838 Published on 2022-9-16 12:42 Infrared emitting tube (IR LED), also known as infrared emitting diode, belongs to the diode category. It can directly convert electrical energy into near-infrared light (invisible...

It is easy to ignore its existence and value when it is always with you.