In a car’s cigarette lighter socket, only for 12V voltage, but the CD, LCD TV, MP3, games, etc. it takes a different supply voltage. Make the following simple converter solves this problem.
Circuit shown in Figure, 12V power supply removed from the car cigarette lighter socket, the second one of the band switch SW1A knife into six three-terminal adjustable regulator input pin LM317, LM317’s adjust pin (ADJ) access by SW1B different value resistor to the power negative terminal. When SW1 at different stalls, the output can be obtained at 1.5V, 3.0V, 5.0V, 6.0V, 9.0V, 12V several voltage for the corresponding low-voltage electrical appliances. LM317 should be installed in the aluminum heat sink (100 × 100 × 25mm), mainly because larger heat 1.5V stalls. Into the appropriate box of the entire circuit, the panel can only set the band switch.
Figure R2 ~ R6 is the output voltage setting resistance, For the other voltage levels can be calculated as follows:
V OUT = (1 + R2/R1) V REF + I ADJ ≌ (1 + R2/R1) V REF
Where V REF is the reference voltage, typically 1.25V, I ADJ to ADJ pin out of the current, typically 50μA, R2 R2 ~ R6 on behalf of one of the figure.
Figure C1, C2 as the vibration capacitor, C3 ripple removal rate and can improve the circuit stability, D1 is the output short circuit protection diode, D2 appears to prevent the higher the output when the input potential damage to the regulator.