# Converting circuit to use different power supply

Joined Nov 11, 2020
1
Hi, I'm just getting into learning the theory behind electronics instead of just tinkering & I have a question that's probably really simple but I can't work out the answer to myself yet. I have a couple of circuits (simple analog audio circuits) I want to combine into one device that use different power supply voltages, and neither of them take the 9v supply I have readily available right now. I know I could simply use a voltage regulator to supply different voltages to different parts of the circuit but I don't currently have any on hand or much disposable income & I'd like to save space on the board if possible regardless. Is this as simple as applying Ohm's law & using 4 or 3/4 times (circuits run off of 1.5v & 12v supplies respectively) the original resistor values or is it more complicated than that? What about capacitor values? These are simple enough circuits I don't imagine I'd have much trouble from that point playing trial & error with regards to swapping out transistors & such.

#### KeithWalker

Joined Jul 10, 2017
2,520
Can you post a diagram of the circuits or give us a detailed description of each please? I can not suggest a solution without more information.
Regards,
Keith

#### dl324

Joined Mar 30, 2015
15,113
Welcome to AAC!
Is this as simple as applying Ohm's law & using 4 or 3/4 times (circuits run off of 1.5v & 12v supplies respectively) the original resistor values or is it more complicated than that?
Voltage dividers are the most inefficient type of power supply you can use. That's the first type of power supply they show us to explain how inefficient they are then we move to progressively more complex circuits.

If you tell us what voltages and currents you need and how tightly the voltages need to be regulated, we can offer some suggestions.

FYI, a 6V battery operated device assumes it's going to be operated above and below that voltage. Fresh 1.5V batteries will measure more than 1.5V when new and the devices will likely operate until the voltage falls below 1.2V. That's why we can usually substitute NiMH batteries for disposables. NiMH have a nominal voltage of 1.2V, but are closer to 1.4 when charged.

A 12V device will usually operate from 13.8V without problems because that's a typical charging voltage for 12V wet lead acid batteries.

If you have NPN transistors and zener diodes, you can build simple voltage regulators.

#### dl324

Joined Mar 30, 2015
15,113
These are simple enough circuits I don't imagine I'd have much trouble from that point playing trial & error with regards to swapping out transistors & such.
Here's a simple zener regulator good for up to about 100mA:

The zener diode is 5.6V, the base emitter junction of the transistor will drop it to about 5V.

I'm just getting into learning the theory behind electronics instead of just tinkering & I have a question that's probably really simple but I can't work out the answer to myself yet.
It works like this. Without D1, R1 would cause Q1 to saturate (act like a switch that's on) and the output voltage would be about 9V. By putting the diode on the base, it prevents the transistor from saturating and regulates the output voltage to be about a diode drop below the zener voltage.

Ask questions if you want more details.

For lower currents, you could omit the transistor, but R1 would have to carry the full load current plus the zener current.

#### AnalogKid

Joined Aug 1, 2013
10,125

Engineers don't take a dump, son, without a schematic.

ak

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#### KeithWalker

Joined Jul 10, 2017
2,520