AP3706 high performance AC / DC conversion chip
Ora pubblicata: 2020-03-17 11:01:20
AP3706 is a high-performance AC / DC conversion control chip provided by BCD company for battery chargers, application adapters, etc. It is available in SOIC-8 or DIP-8 two package types, with functions such as soft start, open circuit, and overvoltage protection. Its pin function is shown in Table 1.
Table 1 AP3706 pin functions
function 1 CS (Transformer) Primary current detection
2 VCC Supply voltage
3 OUT Control switch triode base circuit
4 GND Ground
5 FB Voltage returned from auxiliary coil
6 VDD 5V voltage output by the internal calibrator
7 BIAS Set the internal bias current generated by the external resistor connected to ground
8 COMP Connect a bypass capacitor for (internal) CC circuit operation
The chip uses pulse rate adjustment (PFM) to establish feedback and drive the NPN transistor, so that the power supply works in discontinuous power mode (DCM). It does not require a photocoupler and a secondary control circuit to achieve constant voltage or constant current. Out.
The switching power supply adopting the chip does not need a compensation circuit, has fewer peripheral components, and has higher working efficiency. It is widely used in miniature / wireless phones, LED drive circuits, MP3 and other portable equipment adapters or chargers, as well as backup and auxiliary power equipment. The actual circuit of the AP3706 applied to the TP-Link TL-340G + wireless router power adapter is shown in Figure 1. The following briefly describes its working principle:
220V mains power is sent to AP3706 (U1) ① via R2 and R3 after the voltage is reduced by rectification, and it provides starting power for it. After U1 works, switch signal is output from ③ pin to drive Q1 to work. After Q1 works normally, the feedback winding is supplied with power for U1 after R9 current limiting, D5 rectification, and C12 filtering. At the same time, this circuit also has the function of overvoltage protection, that is, when the voltage of this pin exceeds a certain value, U1 will automatically turn off the output. If the output voltage fluctuates, the feedback winding voltage will also fluctuate. The fluctuating voltage is sent to the ⑤ pin of U1 after the divided voltage of R9 and R10. Compared with the internal voltage, the Q1 on-time is changed to change the extraction voltage. To achieve the purpose of German pressure output. The R16 of Q1 emitter is an over-current sampling resistor. When the working current of Q1 is large, the voltage drop across R16 will increase, and it will be sent to the ① pin of U1 via R14 (protection value is 8V), which is processed internally. After that, the on-time of Q1 is controlled, so as to protect it.
The repair method for the AP3706 switching power supply is similar to the switching power supply for other chips. If the power supply does not work and there is no obvious component breakdown, the reason is mostly the startup resistance or the AP3706 is damaged. If the Q1 breakdown, check the circuit for overcurrent. In addition, the breakdown of the spike absorption circuit consisting of R6, C3, R7, and D7 will also cause Q1 breakdown.Etichetta: AP3706