Principle and production of automotive power converter

Principle and production of  　　automotive power converter

　　The circuit is shown in the figure. 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 ( AD J) of LM317 is connected through SW1B. Insert resistors of different values ​​into 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

　　In the formula, VR EF is the reference voltage, with a typical value of 1.25V, IADJ is the current flowing out of the AD J pin, with a typical value of 50μA, and R2 represents one of R2~R6 in the figure.

　　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. The simple converter made below solves this problem.