Electronic Circuit Design for DC Low-Voltage Stabilized Power Supply

Release time:

2019-07-29

DC low-voltage stabilized power supply electronic circuit designs are widely used in power management. Therefore, today we’ll provide a brief analysis of circuit diagrams for this type of design, hoping it will be helpful to readers when designing similar applications.

　　The rectifier and filter circuit, consisting of VD1–VD4, R1, C1, and C2, forms the switching power supply’s rectification and filtering section. The NE555 along with R2, R3, C4, and VD6 constitutes a multivibrator circuit whose frequency is approximately 20 kHz. R4, C3, and VD5 form a step-down voltage regulator circuit that supplies the NE555 with a 12V operating power source. The high-power transistor VT1 and transformer T comprise the switching circuit. The operating state of VT1 is controlled by pin ③ of the NE555; the turn-on time is determined by the pulse width, which can be adjusted by modifying R3. As the pulse width widens, the output voltage rises; as the pulse width narrows, the output voltage falls. VT2, together with R8, R9, and C6, forms an overcurrent protection circuit. When the load becomes excessively heavy or a short-circuit fault occurs, VT2 turns on, forcing the NE555 to reset and stop oscillating, thereby protecting VT1 from damage. C7 and R10 serve as protective networks to prevent the collector-emitter junction of VT1 from being punctured instantaneously by surge pulses. After rectification and filtering, the two secondary windings deliver outputs of 20V and 12V respectively. To simplify the design, the switching power supply is configured without automatic voltage regulation; its function is similar to that of a transformer, but it achieves a lightweight, isolated step-down effect instead. Voltage regulation is handled by the subsequent voltage-stabilizing circuit. The 12V DC voltage is regulated by the 7805 IC to produce a +5V output, while the 20V DC voltage is fed into an adjustable voltage-regulating circuit.

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