# Use of two power sources in voltage regulator using zener diode

#### The Engineer

Joined Sep 3, 2014
35
I am currently designing a voltage regulator using a 5V zener diode.
I am wondering why some people choose to use two power sources instead of one, what would be the benefits of this ?
the circuit is being simulated on multisim.
the two attachments uploaded are as follows :-
the one with one power source is my circuit which I am looking to improve
the one with two power sources is a friends circuit, I cannot understand why they have used two power sources.

any help with this will be greatly appreciated !

also any advice on possible modifications to the circuit would be great ! I get points for testing circuit in different ways so any advice will help
thankyou
-Connor

#### Attachments

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#### Jony130

Joined Feb 17, 2009
5,230
If you design a fixed positive voltage regulator, then you can use a single supply.

#### ScottWang

Joined Aug 23, 2012
7,005
According to your circuit, a calculation as below:
Vout_741 = 12V - (1.4V~1.8V) = 10.2V~10.6V
Vout = Vout_741 - Vbe = (10.2V~10.6V) - 0.7V = 9.5V ~9.9V
V(-)_741 = Vout /2 = 9.5V ~9.9V = 4.75V~4.95V
So here you have the output voltage around 9.5V ~9.9V.
Is the voltage what you want?
The 2N2222A can't afford too much current, are you just care about the voltage?

#### crutschow

Joined Mar 14, 2008
27,004
The dual supplies are needed if the op amp won't operate properly with a 5.1V input and the minus supply node going to ground (but most will).

What improvements are you looking for?
What's the maximum output load current you want to provide?

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