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.enter image description here

Also if there is any other advice anybody can give me on modifications to this circuit that would be great :) !

Here is an example of a voltage regulator using two power sources:-

enter image description here

Thankyou in advance


  • 1
    \$\begingroup\$ I only see one power source in your schematic. Can you give an example of the two-source circuits you want to know about? \$\endgroup\$
    – The Photon
    Jan 19, 2015 at 16:07
  • \$\begingroup\$ I have uploaded an image of a similar circuit using two sources, I have been told this will improve performance somehow. \$\endgroup\$ Jan 19, 2015 at 16:19

1 Answer 1


The only thing the extra power supply is attached to is the negative rail of the op-amp. This would allow the op-amp to have a much greater voltage output range. If you're near the negative voltage rail of the op-amp in the first circuit, it's possible you'd start clipping. This situation could occur if you're trying to get a very low output voltage from the voltage regulator.

In summary, if your first circuit allows you to go from 1-11 volts regulation, then your second circuit would allow you to got to 0-11 volts of regulation.

The added power supply is somewhat unnecessary if you're not using the regulator near the bottom rail or if you use a rail-to-rail op-amp instead.

  • \$\begingroup\$ Thankyou for your help ! so am I correct in saying the following:- if I was to add another supply to the single supply simulation , and link the zener in between the two supplies, this would allow for a greater bandwidth of regulated voltage \$\endgroup\$ Jan 19, 2015 at 16:40
  • \$\begingroup\$ @FlewittConnor bandwidth is related to frequency. Voltage range is orthogonal to frequency. Adding the extra supply in this manner adds greater low-side regulation capability. You can say it increases the output voltage regulation range depending upon the input voltage. \$\endgroup\$
    – horta
    Jan 19, 2015 at 16:44
  • \$\begingroup\$ I'm with you now :) mix up of terms there. Thanks ! \$\endgroup\$ Jan 19, 2015 at 16:47
  • \$\begingroup\$ @FlewittConnor, if you connect the anode of the zener to the negative input supply, the output voltage regulation will only be as good as the negative supply regulation. If the negative supply value changes, so will the output voltage. Maybe this is what you want, but most often when we design a voltage regulator it's exactly what we're trying to avoid. \$\endgroup\$
    – The Photon
    Jan 19, 2015 at 17:17
  • \$\begingroup\$ @ThePhoton Is the reference point for the anode of the zener a physical connection to earth or something else when the dual supply topology is used? \$\endgroup\$
    – horta
    Jan 19, 2015 at 18:49

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