Maintenance and charging dual-purpose regulated power supply circuit
For home appliance repair personnel, repairing power supplies is essential. However, a professional maintenance power supply is quite expensive. If the power supply is properly improved, a high-quality, low-cost, easy-to-use, and reliable quality regulated power supply for maintenance and charging can be produced. This regulated power supply is introduced to readers for reference. For convenience, the power supply is designed as two independent low-voltage and high-voltage outputs, as shown in the figure. Among them, the low-voltage output is dedicated to the maintenance of low-voltage electrical appliances (such as tape recorders, walkmans, semiconductor radios, etc.) and charging of batteries and rechargeable batteries; the high-voltage output is dedicated to color TV maintenance. Take the low-voltage output as an example to illustrate its working principle. The secondary 32V voltage of the transformer is rectified by VD1~VD4 and filtered by C1 to obtain a DC voltage of about 45V. This voltage is integrated with a three-terminal voltage regulator LM338K to obtain a stable output voltage. Adjust the potentiometer RP1 to obtain 1.25V~ 37V stable DC voltage. In the figure, LED1 is the indicator light of the regulated power supply, R1 is the current limiting resistor of LED1, and C2 is used to filter out the high-frequency harmonic components of the power supply and eliminate parasitic oscillations. VD5 and VD6 are designed to prevent input and output short circuits and protect LM338K. According to the characteristics of LM317T, the input voltage should be increased, and the resistance of the adjustment terminal should be increased appropriately, so that the maximum voltage difference between the input and output terminals does not exceed 40V, so as not to damage the LM317T. Design according to the power supply voltage and component values in the figure. From the output terminal, you can get 90V ~ 130V, DC output current not less than 1A. VD13 is designed to prevent the reverse charging of the capacitor in the color TV from damaging the LM317T. The circuit composed of VD14, LED2 and R5 is not only the indicator light of the high-voltage power supply, but also designed to maintain the minimum operating current of LM317T. When selecting components, LM338K must use genuine products. The maximum output current of the voltage regulator block can reach 5A. The power transformer is best wound by yourself, and the power is not less than 180W. The low-voltage secondary current is greater than 5A, and the high-voltage secondary current is not less than 1A. . The rectifier diode can be 2CZ57D or imported 200V/6A rectifier full bridge. Use 85C1 type 5A meter head for DC current meter, choose 85C1 50V meter head for low voltage meter head, and choose 85C1 150V meter head for high voltage meter head. In addition, LM338K and LM317T should be installed with a large enough radiator. RP2 and S2 in the low-voltage power supply are set for charging the No. 5 battery and the No. 7 battery, and RP2 can use a multi-turn rotary potentiometer. In actual use, in order to prevent overheating and damage to the transformer and voltage regulator block caused by long-time high-current charging, a DC instrument fan can be connected and placed in the air of the machine to dissipate heat.
