A novel and practical DC low voltage stabilized power supply

The VD1-VD4, R1, C1, and C2 of the switching power supply part form a rectifier filter circuit. NE555 and R2, R3, C4, VD6 and other components form a multi-vibrator circuit with a frequency of about 20KHz. R4, C3, and VD5 form a step-down voltage regulator circuit to provide 12V working power for NE555. The high-power tube VT1 and transformer T form a switching circuit. The working state of VT1 is controlled by the ③ pin of NE555. The conduction time is determined by the pulse width. The pulse width can be changed by adjusting R3. When the pulse width becomes wider, the output voltage increases; when the pulse width becomes narrower, the output voltage decreases. VT2 and R8, R9, and C6 form an overcurrent protection circuit. When the load is too heavy or a short circuit fault occurs, VT2 is turned on, forcing NE555 to reset and stop oscillating, thereby protecting VT1 from damage. C7 and R10 are protection networks to prevent the ce junction of VT1 from being broken down by instantaneous pulses. The two secondary windings output 20V and 12V respectively after rectification and filtering.

In order to simplify the production, the switching power supply is designed to be unable to automatically stabilize the voltage. Its function is similar to that of a transformer, but it only realizes the lightweight isolation and voltage reduction function. The voltage stabilization function is realized by the voltage stabilization circuit behind. The 12V DC voltage is stabilized by 7805 and outputs a +5V voltage; the 20V DC voltage is sent to the adjustable voltage stabilization circuit.

The two have different grounds, so they can be combined for addition and subtraction to output a variety of voltages.