This post show how we can make a Simple Regulated Adjustable Power Supply Circuit that can change voltage output.
It use one chip name LM723 also people call it IC 723.
This chip is good because it take different voltage from power plug and make it steady and we also can turn one knob to choose how much voltage comes out.
It help a lot for many electronics project.
Circuit Working:
Parts List:
| Component | Quantity |
|---|---|
| Resistors | |
| 0.56Ω1W | 1 |
| 750Ω 1/4 watt | 1 |
| 2.7k 1/4 watt | 1 |
| Potentiometer 1k | 1 |
| Capacitors | |
| Ceramic 470pF | 1 |
| Electrolytic 2200µF 25V | 1 |
| Semiconductors | |
| IC LM723 | 1 |
| Transistor 2N3055 | 1 |
Potentiometer use for adjusting or changing inside reference level of IC 723 so output voltage stay stable like as follows:
When one slowly move the middle arm of potentiometer closer to ground it change the voltage at the op-amps inverting pin and that make output voltage go up.
When we move pot arm down output does not stay same as reference voltage.
Instead feedback system change inverting pin voltage to match voltage from pot.
If voltage across pot pins go down then output voltage go higher to balance and match needed voltage.
If we move pot center arm more down voltage drop become more, so IC output voltage go more high.
Example if pot arm move two third down then feedback voltage to inverting pin is one third of output.
This way output become 3 times more than reference voltage.
It keep inverting pin at correct level.
So this feedback with pot help make output voltage adjustable and also stable.
How to calculate output voltage:
If want fixed stable voltage one can remove pot and use two resistors R1 and R2 as voltage divider like shown in diagram.
Formula: 1 (R1 + R2) / R2
Volts means how much constant output voltage we want.
R1 connect from output to inverting pin of op-amp and R2 go from inverting pin to negative side (ground) of the device.
This setup make reference voltage go straight to non-inverting input of IC 723s op-amp.
The formula show the reference voltage and lowest voltage IC can give by default.
If we want output voltage less than 7V than one can change this number to whatever low voltage it needs (but not too low).
But remember IC 723 cannot give less than 2V, that is minimum.
So if one want 2V output formula will be like this:
Formula: 2 (R1 + R2 )/ R2
Understanding Current Limit in IC 723:
IC 723 can control output current very nicely based on how much current load one needs.
Some resistors which are chosen with care are used to sense and stop extra current.
This help keep current at safe level.
Formula to find current limit resistor is simple like this:
Rsc = 0.66 / Maximum Current
How to Build:
To build a Simple Adjustable Power Supply Circuit using IC 723 is mentioned below:
Get Components Ready:
- First collect all parts one need like IC, resistors and pot etc.
Put IC 723:
- Place IC 723 on breadboard or PCB.
- Connect pins as per datasheet.
- Mostly connect input voltage, ground, output, reference and adjust pins.
Check Voltage Divider:
- Use two resistors R1 and R2.
- R1 go from output to inverting pin of op-amp.
- R2 go from inverting pin to negative line.
- This make reference voltage.
Add Potentiometer:
- Put potentiometer in circuit.
- One side connects to positive voltage and other side connects to ground.
- Middle pin wiper will connect to inverting pin of op-amp.
- This help adjust reference voltage slowly.
Add Current Limiting Resistor:
- Use this formula: Rsc = 0.66 / Max Current
- Use resistor with this value.
- Put it in series with the load to limit current.
Finish Op-Amp Wiring:
- Connect non-inverting pin of op-amp to reference voltage.
- If needed add extra resistors for stable output.
Connect Power Supply:
- Connect the power source.
- Be careful with + and – sides.
Test Circuit:
- Before full power ON check all wires and parts.
- Then slowly give power.
- Use multimeter to check voltages and be sure they look right.
Adjust Output:
- Turn potentiometer to change voltage.
- See if output voltage stay steady as per ones need
Test Current Limit:
- Put load on output.
- Check if current stay under the limit.
- If not change resistor to fix.
Note:
- Be safe, use good insulation and see for any short circuit.
- Work in place with good air flow.
- If anyone is new to electronics ask someone who is well trained.
Conclusion:
To conclude using IC 723 for adjustable power supply is small and good way to get stable DC voltage one can change.
Because of feedback control and filter parts output voltage stay same even if input or load change.
This circuit is useful and trusted so people use it many places like for delicate devices, lab tools and also in audio systems.