PCB Tech - PCB protection of five high-power devices at this stage

At this stage, the following protection methods are suitable for PCB electronic products, automated electronic control equipment and power semiconductor devices:

1. Fuse method

This is a commonly used protection method. The fuse is often connected in series at the power input end of the circuit to control the total current of all circuits. Its working principle is to cut off the power supply to realize the protection purpose by relying on the increased fault current flowing through the fuse after the circuit has a problem, causing it to heat up and melt by itself. The fuse method has the advantages of simple implementation, easier maintenance, lower cost, and complete power cut off during protection, so it is widely used in all PCB electronic circuits and PCB electronic equipment at this stage.

However, in view of the fact that the total current flowing in the fuse is the total current of the circuit, the change in the operating current of a single power semiconductor device cannot cause its effective response; in addition, due to the slow melting speed of the fuse, only when the power semiconductor device is damaged or a vicious short circuit fault occurs in the circuit. After the fault current has doubled, it will be blown. Therefore, it can only play a role in preventing the further expansion of the fault, and cannot protect the power semiconductor device.

2. Detecting the main circuit current method

This method is to connect detection elements (detection resistors, transformers, etc.) in series at the input of the main circuit power supply, and obtain the corresponding current or voltage signal through the voltage drop or current magnitude of the total current in the detection circuit on the detection element, which is then amplified by the circuit, Compare with the action threshold of the protection circuit to determine whether to protect or not;

In view of the use of electronic technology, this protection method has improved sensitivity and response speed compared with the fuse method, but this method still detects the total current of the circuit, and the working current of the faulty power semiconductor device is only a few minutes of the total current. One or even one tenth, its change cannot cause an effective response of the protection circuit.

Therefore, this method always responds after the PCB fault current is formed, causing the detection result and the protection action to lag, and it cannot meet the protection requirements for power semiconductor devices. Therefore, the protection method is the same as the fuse, and only plays a role in preventing further expansion of the fault after the power semiconductor device has been damaged and the vicious over-current fault occurs. There is still no way to protect power devices.

3. Detecting the working current method of power devices

This is currently a more commonly used method for protecting power semiconductor devices, and has a certain protective effect on power semiconductor devices. This method is to string a detection element (resistance or current transformer, etc.) in the working current path of the protected power semiconductor device, and obtain the current or voltage signal by detecting the working current of the protected device on the detection element, and then processing the circuit. The fault signal is protected by a fuse or shutting off the power supply.

The working principle and circuit structure of the power device working current detection method are the same as those of the main circuit current detection method. The difference is that the detection object is the working current of the protected device, so the sensitivity is higher than that of the main circuit current detection method, and the effect is also better. If the method uses electronic devices to shut off the current path to implement protection, it can play a protective role after the tube has an overcurrent fault.

However, because the scheme still uses the current detection method, that is, the fault signal is detected and protected after the fault is formed and the protected device is impacted by high voltage and large current, which still causes signal acquisition lag. If the power margin of the protected device is small or the circuit failure is serious, the protected device will still be damaged immediately; if the power margin of the protected device is large and the degree of failure is not serious, the device will generally not be damaged

4. Parallel detection of power device voltage method

As the name suggests, this method is that the protection circuit is connected in parallel with the protected power device, and the signal is obtained by detecting the voltage of the protected device when it is working. According to the voltage situation, it is judged whether the circuit is faulty. The protection method adopts the in-situ protection method, that is, through forced Cut off the control signal of the protected power device itself, forcing it to stop working to realize its protection. (Detect the voltage of the protected device and directly protect the protected device)

Because this method detects voltage signals, faults can be found immediately when the circuit is abnormal, and protection is performed when the PCB fault current has not yet formed, avoiding the impact of the fault current on the device.

The protection method also has the following characteristics:

1. The protection circuit is connected in parallel, no components are connected in series in the main working circuit, the power utilization rate is high, and there is no heat source.

2. The detection object is the working voltage of the protected power device, so the input impedance of the protection circuit is high, the power consumption is small, and the detection accuracy is high.

3. What is detected is the working status of the protected object itself, and the protection is directly applied to the protected object, so it is highly targeted, and the protection is timely and reliable.

The disadvantage of this protection circuit is that it only performs qualitative detection of the working state of the protected PCB device. Therefore, if it is used in voltage-controlled power devices, it can only have an ideal protective effect on load short-circuit and serious over-current faults.

5. Parallel type detection working pressure drop method

Due to the on-resistance of the power semiconductor device itself, overload and overcurrent in any situation will cause its saturation voltage drop or working voltage drop to increase, that is, regardless of the working state of the semiconductor device, the device itself will be There is a corresponding working voltage drop value; monitor and monitor the voltage drop when the power semiconductor device is turned on, and the overcurrent and overload situation and degree can be judged according to the magnitude of the voltage drop.

The above is some relevant knowledge of PCB power devices. The continuous development of power devices requires the continuous efforts of our scientific researchers to promote the continuous development of technology and make our PCB electronic products more efficient.