Switching power supply is widely used in various electronic devices, and its overvoltage and overcurrent protection circuits are crucial to ensure the safe and stable operation of power supply and load.
First, the key to the design of overvoltage protection circuit is to be able to detect abnormal increase of output voltage in time. Usually, a combination of voltage regulator diode and resistor voltage divider network is adopted. When the output voltage exceeds the set threshold, the voltage regulator diode is broken down, triggering the subsequent protection action. For example, in a 12V output switching power supply, a voltage regulator diode with a suitable withstand voltage value, such as a 15V voltage regulator tube, can be selected to cooperate with the voltage divider resistor to accurately set the overvoltage protection point. Once the overvoltage is detected, the drive signal of the power switch tube can be cut off through the control circuit to stop the power supply output and prevent the overvoltage from damaging the load equipment.
Secondly, the overcurrent protection circuit is mainly used to monitor the load current. A common design is to use a current detection resistor to convert the load current into a voltage signal. The voltage signal is compared with the set reference voltage. When the current exceeds the limit value, the comparator output signal triggers the protection mechanism. For example, for a switching power supply with a maximum output current of 5A, a current detection resistor with a suitable resistance value, such as 0.1Ω, is selected. When the current reaches 5A, the voltage on the detection resistor is 0.5V, which is compared with the reference voltage of 0.5V to trigger the protection. The power supply can be shut down or the current output can be limited to avoid overheating and damage of the power device due to excessive current.
In the design process, the response speed of the protection circuit is an important consideration. Fast response can take measures at the moment of abnormal situation, minimizing the damage to the power supply and load. Therefore, it is crucial to select high-speed comparators and low-latency control components.
For the testing of the protection circuit, special test equipment is required. For example, electronic loads can simulate various load conditions, including overcurrent conditions; high-voltage sources can be used to simulate overvoltage conditions. When testing overvoltage protection, gradually increase the output voltage to observe whether the protection circuit operates accurately at the set voltage point, and check whether the power supply stops output and has no abnormal damage. When testing overcurrent protection, adjust the electronic load to gradually increase the current, verify whether the protection circuit responds in time when the current value is set, and check whether the power supply can resume normal operation after the abnormality is removed after the protection action.
In addition, the stability and reliability of the protection circuit also need to undergo a long-term aging test. Under different ambient temperature and humidity conditions, continuously run the switching power supply and simulate multiple overvoltage and overcurrent conditions to ensure that the protection circuit can always work normally without malfunction or failure.
In short, the design of the overvoltage and overcurrent protection circuit of the switching power supply needs to comprehensively consider multiple factors, and verify its effectiveness and reliability through rigorous testing to provide reliable power supply protection for electronic equipment.
