Nov 172020

12V to 9V DC Converter

This 12V to 9V DC converter is very useful to power 9V DC devices in a car that uses a 12V battery. The maximum current consumption allowed by this circuit is 0.8 amps. This 12V to 9V DC converter is implemented using a zener diode and a NPN bipolar transistor (Q1) as shown in the circuit diagram.

To better understand the operation of this circuit, the following article is recommended: Zener voltage regulator.

How the 12V to 9V DC Converter works?

As in the zener voltage regulator from the above suggested link, a series resistor is used (R1 and R2 are used in parallel in this case).

The output voltage of the circuit is the zener diode voltage plus the transistor base – emitter voltage. (Vout = Vz + Vbe). Vout = 8.2 + 0.7 = 8.9 volts.  A greater variation of the output current is allowed using the NPN transistor. This is not the case when the zener diode is used alone.

12V to 9V DC Converter Circuit


  • Use a heatsink as large as possible for the Q1 transistor.
  • The converter input voltage must not exceed 14 Volts.

TIP41C NPN transistor Pinout

TIP41C NPN Bipolar Transistor Pinout

List of components for the 12V to 9V DC converter

  • 1 TIP41C NPN bipolar transistor or similar (Q1).
  • 2 6.8 ohm resistors (5 watts or more) (R1, R2).
  • 1 1N756 zener diode 8.2 volts or similar (D).
  • 1 heatsink to be used on the Q1 transistor (required).

Suggested printed circuit board (PCB)

The following diagrams show a suggested printed circuit board (PCB) and an approximate view of the final circuit appearance.

12vdc to 9vdc Converter PCB

12vdc to 9vdc converter circuit PCB

You may also like the 12 volts to 5 volts converter circuit, that uses de lm7805 voltage regulator IC.

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