# Voltage Regulator

#### artmaster547

Joined Jan 6, 2016
409
Hi all

I am trying to create a regulator I have a supply that is 9V but can vary between 12 and 6, I have attempted something below but it's not functioning in the way I intend any guidance or alternatives would be really appreciated. I want the regulator to output 9V or something close to this as long as it's consistent at the output with the range of inputs 6v-12v.
Thanks
Art

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#### artmaster547

Joined Jan 6, 2016
409
Sorry I would like to make an amendment not 9v I meant 4 volts apologies about this

#### DickCappels

Joined Aug 21, 2008
8,861
If you want the regulator to output 9V then you will have to supply its input with more than 9 volts. Generally, you will need 11 or 12 volts input for this circuit.

Also: You will have to adjust the feedback divider to get 9 volts out assuming 6.9 volts on the base of Q1. The ratio will not be exact because of base current into Q1, and

You will probably have to decrease R1 to get enough current (figure 5 to 10 ma) into D1 to get its voltage close to 6.2 volts.

#### dannyf

Joined Sep 13, 2015
2,197
Your zener is of the wrong voltage.

Simpler approach is to use a 3 terminal regulator.

#### DickCappels

Joined Aug 21, 2008
8,861
Post-amendment comment (now that we know you want 4 volts out).

Change D1 to a 3.3 volt Zener (make sure you run enough current to get 3.3 volts), and omit R3. You can also replace R4 with a short. Vbe Q1 = about 0.6 volts, Vz D1 = about 3.3V, the sum being equal to 3.9 volts.

#### artmaster547

Joined Jan 6, 2016
409
ge D1 to a 3.3 volt Zener (make sure you run enough current to get 3.3 volts), and
Should I get rid of Q2 as well then?, or should that be the same as Q1, and to get D1 to 3.3V do I change the diode or the resistor that control the current flow

Thanks Art

#### artmaster547

Joined Jan 6, 2016
409
un enough current to get 3.3 volts), and omit R3. You can also replace R4 with a short. Vbe Q1 = about 0.6 volts, Vz D1 = about 3.3V, the sum
Could you provide a drawing by any chance would really appreciate it thanks
Art

#### dannyf

Joined Sep 13, 2015
2,197
You can use a led in place of the zener, as 3.3v is still a little too high for what you want to do. And an led also functions as a power indicator.

Or you can simply short the zener.