12VDC to 9VDC Converter
This 12VDC to 9VDC converter is very useful for powering 9VDC devices in a car that uses 12VDC battery. The maximum current consumption allowed by this circuit is 0.8 amps.
This 12VDC to 9VDC converter is implemented using a zener diode and a NPN bipolar transistor as shown in the circuit diagram.
To understand the operation of this circuit, the following article is recommended: Voltage regulator with zener diode.
How the 12VDC to 9VDC Converter works?
As in the voltage regulator with zener, from the suggested link above, a series resistor is used (on this case, R1 and R2 are used in parallel).
The output voltage of the circuit is the zener diode voltage plus the emitter – base voltage of transistor Q1. (Vout = Vz + Vbe). Vout = 8.2 – 0.7 = 8.9 volts. The NPN transistor allows a greater variation of current demand from the load, than when only the zener diode is used.
- Use a heatsink as large as possible for transistor Q1.
- The converter input voltage must not exceed 14 Volts.
List of components for converter 12VDC to 9VDC
- 1 TIP41C NPN bipolar transistor or similar (Q1)
- 2 6.8 ohm resistors (5 watts or more) (R1, R2)
- 1 8.2 volt zener diode 1N756 or similar (D)
- 1 Heatsink for transistor Q1 (required)
Printed circuit for 12VDC to 9 VDC converter
The following diagrams shows a suggested printed circuit board (PCB) and an approximate view of the final circuit appearance.