Research on control strategy of switching power supply

Switching power supply Control mode

Switching power supply in normal operation, the load in the external interference will produce fluctuations, how to ensure that the load fluctuations in the condition of the output stability needs to control the knowledge of the theory to solve. In the design of switching power supply applied to the control mode mainly divided into two: one is to monitor the output voltage, adjust the PWM duty ratio, to ensure the stability of the output voltage, that is, voltage control. The other is to monitor the voltage while adding current monitoring, adjust the PWM duty ratio, that is, the current control mode. The choice of the control mode depends on the specific load object, the pure voltage control or current control mode can not be applied to a variety of specific types of load. Voltage control mode

Voltage control mode, the size of the output voltage is a critical amount. Principle as shown

The focus of the voltage control mode is to monitor the value of the output voltage, the v_f of the load end as the input of the error amplifier, the other input of the error amplifier is the reference voltage V_ref, the comparison is sent to the PWM controller input and fixed sawtooth wave signal processing, The PWM signal is generated to control the conduction and shutdown of the switching tube, thereby realizing the voltage regulation.
The advantages of voltage control mode are very prominent, there are simple control ideas, single circuit structure and low output impedance. But the voltage feedback also has the disadvantage of phase delay, the corresponding speed is not fast enough, the design of loop compensation network is often too complex, and also need to design the overcurrent protection circuit separately. Current control mode

Current control mode, output voltage and primary winding current are critical quantities. Principle as shown

The focus of the current control mode is to monitor the voltage while introducing the monitoring of the current. The voltage sent to the current comparator on the sampling resistor is compared with the output of the voltage error amplifier to control the PWM size, thereby achieving the voltage stability and the current in the appropriate range.
Current control mode is a double closed-loop control system, compared to the voltage control mode, the voltage regulation rate is higher, the adjustment speed is faster, although to some extent, increase the complexity of the circuit, because the current mode does not need to design a separate current protection.