Useful Information | 5 Common Protection Circuits (with Circuit Diagrams)

木犯001号

Useful Information | 5 Common Protection Circuits (with Circuit Diagrams) [Copy link]

In the real world, the environment around electronic circuits is always unpredictable. Human static electricity, lightning surges, misoperation and many other unpredictable factors always threaten the normal operation of electronic equipment. Therefore, the role and significance of protection circuits are very important. After years of development, protection circuits have gradually developed from the simplest fuses to the various complex devices today, each of which plays a different role. Today, let us take a look at how they can stably protect our daily lives!

1. Short circuit protection

The main function of the short-circuit protection circuit is to disconnect the closed circuit in time when a short circuit occurs in the circuit system to ensure the safety of subsequent devices.

When a short circuit occurs in the power system, the current in the circuit will instantly increase to several times or even more than ten times the normal level. We can use this feature to insert a fuse in series in the circuit . When the current increases to the fuse's breaking current, the fuse will melt due to its own overheating, thus disconnecting the circuit. This is one of the most common protection circuits .

However, this type of fuse has a disadvantage: when the fuse blows, the engineer must manually replace it with a new one after troubleshooting, which is very inconvenient in some narrow spaces, so the "resettable fuse" was born. After the fuse blows, it will be reconnected as the temperature drops, so that the power switch can be disconnected when a fault occurs, and the power switch can be turned on again after troubleshooting. How does the resettable fuse achieve "self-recovery"?

The resettable fuse is composed of specially treated polymer resin and conductive particles distributed inside it.

Under normal conditions, the polymer resin tightly binds the conductive particles outside the crystalline structure to form a chain-like conductive path. At this time, the resettable fuse is in a low-resistance state. The heat energy generated by the current flowing through the resettable fuse on the line is small and will not change the crystal structure. When the line is short-circuited or overloaded, the large current flowing through the resettable fuse generates heat to melt the polymer resin, rapidly increase in volume, form a high-resistance state, and rapidly reduce the working current, thereby limiting and protecting the circuit. Therefore, the protection circuit composed of the resettable fuse can also bear overheating and overcurrent protection.

2. Overvoltage protection

Overvoltage protection refers to a protection circuit that automatically disconnects the power supply circuit when the power supply voltage exceeds the rated voltage. In electronic circuit design, a common protection method is to use Zener diode overvoltage protection. As shown in Figure 2-1:

Figure 2-1

The 1N4099 is a 6.8V diode, if the input exceeds 6.8V, the output will be clamped around 6.8V.

3. Anti-reverse connection protection

Many electronic components do not allow the positive and negative poles of the power supply to be reversed. In the designed circuit board, if the external interface does not have a reverse connection protection design, users can easily connect the positive and negative poles incorrectly during use, causing the device to burn and cause property losses. The principle of the reverse connection protection circuit is to rectify the power supply to a certain polarity at the front stage of the power input and then connect it to a fixed back stage. As shown in Figure 3-1:

Figure 3-1

Another anti-reverse connection method is to automatically shut down when the power is reversed, as shown in Figure 3-2:

Figure 3-2

This circuit uses a MOS tube to shut down. Since the parasitic diode voltage drop of the MOS tube is small, it can withstand a larger current during normal use.

4. Lightning surge protection

Lightning is one of the most serious natural disasters. Early electronic devices such as televisions and refrigerators were severely damaged by it. In my childhood memories, I often heard that televisions were damaged after thunderstorms. With the development of technology, this situation almost never happens in daily life. This is thanks to the lightning surge protection circuit.

When lightning strikes, the zero potential near the grounding point will be raised, causing unstable power supply voltage. If lightning strikes near the power line, the induced voltage generated should not be underestimated. The waveform of the surge is very similar to the sudden waves on a calm beach, which we figuratively call a surge.

In order to eliminate this surge voltage, the more commonly used devices are: discharge tubes , varistors , TVS , common mode inductors and other devices.

The protection principle of the discharge tube, varistor and TVS is that when the voltage exceeds a threshold, the resistance of the device will decrease rapidly. We connect the device in parallel in the circuit to provide a discharge channel to the ground. The common mode inductor uses the characteristics of the inductor to only allow two voltages of the same phase and opposite amplitude to pass through. The surge is generally two identical signals, so the surge will be suppressed. Common mode inductors are usually used in the post-stage of devices such as discharge tubes and varistor.

The common mode surge suppression circuit is shown in Figure 4-1:

Figure 4-1

5. Electrostatic protection

Electrostatic discharge often occurs when the human body touches electronic equipment, especially in winter. In fact, voltages of thousands of volts are similar to the lightning surge mentioned above and can also be handled with the above solution.

no814987

The host gave a good lecture, the content was very detailed and easy to understand, I learned a lot.

dsl7392

This is a very good and often used circuit.

kalin2023

1. Programming and adjusting the patch machine: According to the sample BOM patch position map provided by the customer, program the coordinates of the location of the patch components, and then compare the first piece with the SMT patch processing data provided by the customer. 2. Printing solder paste: Use a steel mesh to leak the solder paste onto the pads of the PCB board where the electronic components SMD need to be soldered, to ensure the uniformity, flatness and consistency of the paste after printing, and to prepare for the soldering of components. 3. SPI: Solder paste detector, detect whether the solder paste printing is good, whether there are poor phenomena such as insufficient tin, tin leakage, and excessive tin, and timely screen out PCBs with poor printing 4. Patch: Accurately install the electronic components SMD to the fixed position of the PCB. 5. High-temperature solder paste melting: It is mainly to melt the solder paste at high temperature, and after cooling, the electronic components SMD and the PCB board are firmly soldered together. 6. AOI: Automatic optical inspection instrument detection is to detect whether the components after soldering have poor soldering, such as tombstone, displacement, empty soldering, etc. through a computer. 7. Visual inspection: The key items of manual inspection include whether the PCBA version is the changed version; 8. Packaging: The qualified products will be packaged separately. The packaging materials generally used are anti-static bubble bags, anti-static cotton, and blister trays.

lanhua

Five common protection circuits

Another important protection is overcurrent (overload) protection!