Voltage Regulator

Thread Starter

artmaster547

Joined Jan 6, 2016
410
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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DickCappels

Joined Aug 21, 2008
6,099
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.
 

DickCappels

Joined Aug 21, 2008
6,099
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.
 

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.
 

Thread Starter

artmaster547

Joined Jan 6, 2016
410
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.
Thank managed to get something working now thank you so much all of you for the help
 
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