Switching regulated power supply circuit

The series-connected regulated power supply we studied earlier, because the adjustment tube works in the amplification state, is equivalent to a variable resistor in the circuit that can automatically adjust its resistance
. The tube consumes a lot of power and has low efficiency. The switching tube of the switching power supply is either saturated or cut off + the power consumption of the tube is small and the efficiency is high. This kind of
voltage stabilizing circuit that uses the switching principle is a switching stabilized power supply .
    (1) Circuit composition The structure of a series switching regulated power supply is as shown in the figure. In the figure, T is the power transformer, VDl-VD4 are
the rectifier bridge, c] and Cz are the capacitor filter, VT is the switching tube, the working state is controlled by the base control pulse signal U, and the control pulse signal A comes
from the control circuit . The control circuit is controlled by the output voltage, VI) is the freewheeling diode, and L is the choke inductor.
    (2) Working principle The core part of the switching power supply is an inverter that works in a switching state, which can invert DC current into high-frequency
pulse current. When the power is turned on, Ui is input, and U" is less than the upper limit allowable value Uam" at this time. Through the action of the control circuit, the control
pulse signal at the base of the switch tube is high level, and VT is in a saturated conduction state. U． Charge to C via VT and L, forming output current L and output voltage T Ua.
    H increases with time. When it rises to the upper limit allowable value Uonwx, through the action of the control circuit, the control pulse signal "t" of the base of the switch tube
is low level, and V1' is in the cut-off state. Due to the choke inductor L The current in L cannot change suddenly. L produces a self-inductance voltage." ． HI. The polarity of
is shown in Figure 12-26. The freewheeling diode VD is turned on due to forward bias. qL freewheels through RL and VD, and cz is discharged at the same time, thereby maintaining
the continuity of the load current during the switch off period, but the current and voltage gradually decrease.
    When UQ drops to the lower limit allowed value U0. ． . At this time, through the action of the control circuit , Uk is at a high level, and Vr goes to the saturated conduction state. c2 is charged again
. At this time, the freewheeling diode VD network is reverse biased and cut off, and Uct rises again. When U. When it rises to U~;, the control pulse signal "k" changes to low
level. Repeatedly, the circuit is in the switching state, so that the output voltage U0 always keeps fluctuating between the allowed U~~U0 land. The range of fluctuation
is generally within millivolt level to achieve voltage stabilization.