Ringing switching power supply constant current drive circuit

In the ringing switching power supply, the loss of the drive circuit that supplies the base current of the switching transistor is considerable. In addition to ensuring that the switching transistor can fully conduct at the lowest input voltage, the voltage UB on the transformer coil NB is proportional to the input voltage Ui. When Ui rises, the drive current Id also increases, and the loss caused by the increased base resistance Rb increases with the square of the increase in Id. When the driving current ID increases, the current of the Zener diode branch will inevitably increase, which is likely to cause oscillation problems, that is, the switch will work in a certain period of time, and the switch will stop working in the next adjacent period of time. This cycle continues over and over again, and the oscillation frequency is approximately several hundred to several thousand hertz. To solve these problems, that is, when the input voltage changes, constant current driving can be used to keep the driving current basically unchanged, as shown in the figure below. This is essentially a simple series regulator. Its load is a fixed resistor RB. Even if the input voltage Ui changes, the current flowing through RB is constant. This can not only greatly reduce the loss on the resistor, but also prevent intermittent oscillation. The power supply can work continuously and normally within the range of AC 100~200V.