There are over 2,000 power supply manufacturers in Guangdong Province, which means that there are many different specifications and quality levels of power adapters on the market. Sometimes, even adapters with the same output voltage and current can have a large price difference due to different circuit designs, grades of materials used, and production costs. Like other electronic products, switch-mode power adapters also have high, medium, and low-end models. Below, I will introduce some protective functions of high-end power adapters (which low-end adapters do not have).
To properly evaluate the quality of power adapters and chargers, the main principles should be longevity, safety, reliability, and meeting output parameters. To ensure that power adapters can work safely and normally in different working environments and unexpected situations, we must add various protective circuits to the design of power adapters. The protective circuits of switch-mode power adapters can be divided into internal and external protection. The internal protective circuits of the chip include overheat protection circuits for power devices, buffer circuits for voltage and current protection, shut-off/automatic restart circuits, and overcurrent protection circuits. External protective circuits mainly include output overvoltage protection circuits, input undervoltage protection circuits, output overcurrent protection, start-up current limiting protection circuits, soft-start circuits, electromagnetic interference filters, and leakage current clamp protection circuits. There are many types of protective circuits and design structures for switch-mode power adapters, and it is necessary to fully consider the national and regional power grid environments to choose suitable protective circuits and design structures so that the protective circuits can function properly.
Internal protective circuits of power chargers:
Undervoltage lockout circuit: prepares the IC chip before the power adapter outputs normal voltage and current.
Programmable state controller: switches between working and standby states through manual control, microcontroller operation, digital circuit control, or prohibition.
Overcurrent protection circuit: limits the maximum working current of the power MOS tube to avoid breakdown.
Shut-off/automatic restart circuit: restarts the power supply and restores normal operation when the circuit is out of control.
Overheat protection circuit: when the temperature of the power semiconductor or IC chip exceeds the maximum operating temperature of the chip, the circuit is in a resonant state and does not work. The output of the power supply is turned off until the temperature drops, and then it continues to work. It is self-recovering.
External protective circuits of power chargers :
Output overvoltage protection circuit: limits the output voltage to not exceed the set rated value using a thyristor (SCR) or voltage regulator.
EMI filter: suppresses electromagnetic interference from the power grid and the charger itself, and suppresses internal interference. These interferences can be transmitted to other electronic devices through the power cord and cause interference.
Output short-circuit protection circuit: when the load electronic device has an abnormal circuit, the power charger enters a resonant state and stops working to prevent further damage to the electronic device and avoid major accidents such as fire and combustion.
Start-up current limiting protection circuit: uses soft-start power components to buffer the instantaneous charging current of the input rectifier and filter circuit.
Leakage current clamp protection circuit: absorbs the spike voltage generated by the leakage and clamps the drain-source voltage of the MOSFET power switch tube to avoid damage to the power switch tube of the switch-mode power supply caused by instantaneous high pulse voltage.
Overcurrent protection device: such as a fuse tube, self-recovery fuse tube, or fuse resistor. When the input current of the switch-mode power supply exceeds the rated value, the input circuit is cut off. Or when the output current of the switch-mode power supply exceeds the rated value, the power supply automatically shuts down to protect the equipment.
Soft-start circuit: uses a soft-start capacitor to smoothly increase the output voltage when the power is turned on.
Input undervoltage protection circuit: uses the feedback winding of an optocoupler or high-frequency transformer for feedback control to achieve undervoltage protection when the input voltage is too low.
ESD protection circuit: prevents damage to key semiconductor IC components due to human body electrostatic discharge (ESD).
Heat sink: installs suitable metal heat sinks for power semiconductor IC chips, power switching tubes, and output rectifier tubes to prevent overheat protection or damage to the chips due to long-term overheating. Copper material is mostly used for heat sinks, which has a much better heat dissipation effect than aluminum plates.
Post time: May-24-2023