Hysteresis Current Control of High Frequency Switching Power Supply

Taking the Buck PWM converter as an example, the principle circuit diagram of its hysteresis current control is shown in Figure 1. The voltage loop is not drawn in the figure. The hysteresis current control also detects the inductor current and compares it with the current set value UE, and then inputs it to the hysteresis comparator or hysteresis logic element.

Figure 1 Principle circuit diagram of hysteresis current control

In order to realize hysteresis current type control, the upper limit value Ue max and the lower limit value Ue min must be set in the hysteresis comparator. When the detection signal of the inductor current iL drops to the lower limit value Ue min, the comparator outputs a high level, turning on the power switch tube V, and the inductor current iL rises; conversely, when the detection signal reaches the upper limit value Ue max, the comparator outputs a low level, turning off the power switch tube V, and the inductor current drops. The detected inductor current determines the turn-off and on-time of the switch tube V.

Under the hysteresis control mode, the PWM converter works at variable frequency, and its switching frequency generally changes with the input voltage, output voltage and load. Therefore, the design of input and output filters is relatively complicated.

Hysteresis current type control is suitable for variable frequency systems, such as motor drives.