Current controlled switching power supply design

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The current-controlled switching power supply system has three control modes: peak current control, average current control, and hysteresis current control. Figure 1 shows the block diagram of the current-mode controlled switching power supply system. It contains two negative feedback control loops: the inner loop is the current loop and the outer loop is the voltage loop.

The output control signal ue of the voltage controller is used as a given signal of the current loop; the current loop is composed of current detection (such as DC current transformer), processing (IU conversion), and current controller; the detected current can be the inductor current iL It can also be the current iv of the main switch tube, and the detected current (iL or iv) is converted into the voltage iLRi or ivRi through the current detecting resistor Ri, and then compared with the current given signal ue, and the error obtained is obtained. After the signal is amplified by the current controller, it is modulated by the PWM pulse modulator to generate a duty cycle d to control the on/off of the main switching transistor V of the switching converter. For the sake of simplicity, this article only introduces continuous conduction mode (CCM).

Figure 1: Block diagram of a current-mode controlled switching power supply system

The power system block diagram shown in Figure 2 is a block diagram of a current-mode controlled switching power supply system, that is, a frequency domain model of a switching power supply system. In the figure, kv(s) is the transfer function of the voltage controller (compensation network); ki(s) is the transfer function of the current controller (compensation network); Fv and Fm are the transfer functions of the voltage detecting element and the pulse width modulator respectively. ; Ri is the current sampling resistor.

Figure 2: Block diagram of a current-mode controlled switching power supply system