Switching power supplies can be divided into voltage-controlled and current-controlled types in terms of control methods, and single-ended and double-ended types in terms of how the isolation transformer is driven. In these circuit forms, many forms of switching power supply need to use current sensors to detect the current, or for pulse duty cycle control, or for the circuit protection.

current-controlled switching power supply directly on the input pulse current detection, according to the input voltage and output voltage changes at the same time to adjust the pulse duty cycle has a dynamic response speed, the input voltage fluctuations on the output voltage has a small impact on the characteristics.

Current-controlled switching power supplies require a current sensor to detect the input pulse current as a feedback signal for the switching power supply to adjust the pulse duty cycle and stabilize the output voltage. Figure shows the input channel schematic of a current-controlled flyback switching power supply. When the power switch T is on, the current flowing through the primary winding W of the isolation transformer will cause a voltage drop US on RS, which is the input current feedback signal to the switching power supply controller. According to the output voltage feedback signal and input current value feedback signal US. switching power supply controller will be integrated to adjust the pulse duty cycle of the circuit to ensure the stability of the output voltage.

double-ended switching power supply bi-directional drive isolation transformer, can effectively improve the efficiency of the use of isolation transformers, reduce the size of the isolation transformer. In order to prevent isolation transformer bias saturation, double-ended switching power supply often requires a current sensor to detect the bidirectional pulse current input to the isolation transformer for current balance control and circuit protection. Figure shows the anti-bias schematic of a push-pull switching power supply. The circuit uses resistor RS as the current sensor, and when power switches T and T are turned on in turn, the currents I and I flowing through the primary winding W and W of the isolation transformer respectively will be fed back to the bias control circuit by resistor RS in the form of voltage US. Once the difference between the two currents is too large or the current value of one way is too large, it means that the isolation transformer has a bias magnetic saturation phenomenon, and the bias magnetic control circuit adjusts the on-off duty cycle of power switch T or T to make the bi-directional magnetic induction of the isolation transformer balanced. in order to improve the reliability of switching power supply work, to prevent the output current overcurrent and other situations, many switching power supply in the output terminal access current sensor to detect the size of the output current, once the output current exceeds the design standard, the protection circuit is to take the necessary measures to protect the safety of switching power supply. In addition, when the switching power supply as a battery charger, also need to detect the size of the output current, so as to understand the battery charging situation, timely switching charging mode, to improve the charging efficiency and extend the life of the battery effect.