Car power 1.5V-12V six-speed converter

The voltage obtained from the car cigarette lighter is a 12V DC voltage, and general 12V low-voltage electrical appliances can be used directly. However, some CDs, MP3s, MP4s, etc. require different power supply voltages, such as 3V, 6V, etc. The simple converter made below can solve this problem.

The circuit diagram is shown above. The 12V power supply is taken out from the car cigarette lighter socket and sent to the input pin of the adjustable three-terminal voltage regulator LM317 through SW1A, one of the two-pole six-position band switches. The adjustment pin (ADJ) of LM317 is connected to resistors of different resistance values ​​to the negative end of the power supply through SW1B. When SW1 is in different gears, 1.5V, 3.0V, 5.0V, 6.0V, 9.0V, and 12V voltages can be obtained at the output end for use by corresponding low-voltage electrical appliances. LM317 should be installed on an aluminum radiator (100×100×25mm), mainly because it generates more heat at 1.5V. The entire circuit is installed in an appropriate small box, and only the band switch is set on the panel.

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

VOUT=(1+R2/R1)VREF+IADJ≌(1+R2/R1)VREF

Where VREF is the reference voltage, typically 1.25V, IADJ is the current flowing out of the ADJ pin, typically 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 regulator when the output terminal has a higher potential than the input terminal.