Automotive power converter circuit design

Circuit principle: The 12V power supply is taken out from the car cigarette lighter jack and sent to the input pin of the adjustable three-terminal voltage regulator LM317 through SW1A, one of the two-pole six-bit band switches. The adjustment pin (ADJ) of LM317 is connected to different voltages through SW1B. resistor to the negative terminal of the power supply. When SW1 is in different gears, several voltages of 1.5V, 3.0V, 5.0V, 6.0V, 9.0V, and 12V can be obtained at the output end for use by corresponding low-voltage electrical appliances. LM317 should be installed on an aluminum heat sink (100×100×25mm), mainly because it generates more heat at the 1.5V level. The entire circuit is put into a suitable small box, and only the band switch is provided on the panel.

R2~R6 in the figure are the output voltage setting resistors. If other levels of voltage are required, they can be calculated as follows:

VOUT=(1+R2/R1)VREF+IADJ≌(1+R2/R1)VREF where VREF is the reference voltage, typical value is 1.25V, IADJ is the current flowing out of ADJ pin, typical value is 50μA, R2 represents R2~ in the figure One of R6. In the figure, C1 and C2 are anti-vibration capacitors, C3 can improve the ripple removal rate and circuit stability, D1 is the output short-circuit protection diode, and D2 prevents damage to the voltage regulator when the output terminal has a higher potential than the input terminal. The cigarette lighter jack in the car can only obtain 12V voltage, but CDs, LCD TVs, MP3s, game consoles, etc. require different power supply voltages.