You’re traveling and you forgot to bring DC to DC converter in your car, but you need it. This simple DC to DC converter circuit can help you.
This DC to DC converter circuit enables transistorized items such as radio, cassettes, and other electrical devices to be operated from a car’s electrical supply. The table gives values for resistors and specified diode types for different voltage. Should more than one voltage be required a switching arrangement could be incorporated. For high currents, the transistor should be mounted on a heatsink.
I’m assuming this is an NPN xsistor and that the emitter is connected to the +V out terminal…?
Here’s another interesting variation on a DC > DC zener regulator:
http://www.eleccircuit.com/simple-step-down-dc-converter-multi-voltage/
Thanks,
– S.