This post shows you how to build a special power supply circuit that can adjust the voltage it gives out.
It uses a special chip called a LM723 sometimes called an IC 723.
This chip is great because it can take a changing voltage from your power outlet and make it steady, and you can also turn a knob to adjust how much voltage power it gives out.
This is useful for powering many electronics projects.
Circuit Working:
Parts List:
| Component | Quantity | Specifications |
|---|---|---|
| Resistors | ||
| 0.56Ω | 1 | 1W |
| 750Ω | 1 | 1/4 watt |
| 2.7k | 1 | 1/4 watt |
| Potentiometer | ||
| 1k | 1 | |
| Capacitors | ||
| Ceramic 470pF | 1 | |
| Electrolytic 2200µF 25V | 1 | |
| Semiconductors | ||
| IC LM723 | 1 | |
| Transistor | ||
| 2N3055 | 1 |
The potentiometer serves the purpose of finely tuning or, modifying the internal reference level of the IC 723, ensuring a stable output from the IC as follows:
By gradually moving the slider arm of the potentiometer towards ground it influences the inverting pin of the op amp causing the output voltage to rise.
As the potentiometer slider is moved downward along its track instead of stabilizing the output at a voltage identical to the reference voltage the feedback loop adjusts the inverting input of the op amp to match the voltage developed by the potentiometer.
With a reduced potential across the potentiometer pins, the output voltage is prompted to increase aligning the inverting input to the appropriate voltage level.
Further movement of the pot center wiper arm downward results in a proportionally higher voltage drop, causing the output voltage from the IC to rise accordingly.
To illustrate this, suppose the pots center wiper is moved two thirds down.
This action might result in a feedback voltage to the op amps inverting pin being one third of the output voltage.
This mechanism stabilizes the output at a potential three times higher than the reference voltage ensuring the appropriate voltage level on the op amps inverting input.
Hence, this feedback control via a potentiometer facilitates adjustable output voltage with efficient stabilization.
Output Voltage Calculation using formula for a fixed constant stabilized output voltage the potentiometer can be replaced with a potential divider network using R1 and R2 resistors as depicted below:
Formula: 1 (R1 + R2) / R2
Volts determines the desired constant output voltage where R1 is connected between the output and the inverting input of the operational amplifier, and R2 is connected between the inverting input and the negative supply line of the device.
This arrangement links the reference voltage directly with the non inverting input of the IC 723 internal op amp.
The number 7 in the formula signifies the reference value and the minimum output voltage the IC can produce.
To obtain fixed output voltages lower than 7V this number can be substituted with the desired minimum voltage value in the formula.
However, the minimum output voltage for IC 723 cannot be less than 2V.
Thus, the formula for setting the output at 2V becomes:
Formula: 2 (R1 + R2 )/ R2
Understanding the Current Limiting Feature in IC 723:
The IC 723 provides precise adjustable current control at the output based on the load requirement.
A set of discretely calculated resistors are utilized for sensing and limiting current to desired levels.
The formula for determining the current limiting resistor is basic and is as follows:
Rsc = 0.66 / Maximum Current
How to Build:
To build Simple Regulated Adjustable Power Supply Circuit using IC 723 steps are mentioned below:
Prepare Components:
- Gather all the necessary components mentioned above.
Connect IC 723:
- Place the IC 723 on the breadboard or PCB.
- Connect its pins as per the datasheet.
- Typically, this involves connecting the input voltage, ground , output voltage , reference voltage , and adjustment pins.
Set up Voltage Divider:
- Connect a potential divider network using resistors R1 and R2.
- R1 should be connected between the output and the inverting input of the op amp, while R2 is connected between the inverting input and the negative supply line.
- This establishes the reference voltage.
Integrate Potentiometer:
- Integrate the potentiometer into the circuit.
- Connect one end of the potentiometer to the positive supply voltage and the other end to ground.
- The middle terminal wiper connects to the inverting input of the op amp.
- This allows for fine tuning of the reference voltage.
Set Current Limiting Resistor:
- Use the formula provided (Rsc = 0.66 / Maximum Current) to calculate the appropriate resistor value for current limiting.
- Connect this resistor accordingly in series with the load.
Complete Op Amp Setup:
- Connect the non inverting input of the op amp to the reference voltage.
- Connect feedback resistors as necessary for stability based on the op amp used.
Power Supply:
- Connect the power supply to the circuit ensuring polarity is correct.
- Before fully powering up the circuit, double check all connections for correctness.
- Then, gradually apply power and use a multimeter to measure voltages at various points in the circuit to ensure they match expectations.
Adjustment:
- Use the potentiometer to adjust the reference voltage as needed.
- Verify that the output voltage stabilizes at the desired level.
Current Limit Testing:
- Apply a load to the output and verify that the current stays within the desired limit.
- Adjust the current limiting resistor if necessary.
Note:
- Ensure safety precautions are followed when working with electricity such as using appropriate insulation, avoiding short circuits and working in a well ventilated area.
- If you are not experienced with electronics consider seeking assistance from someone with expertise.
Conclusion:
In conclusion, a regulated adjustable power supply circuit utilizing the IC 723 voltage regulator offers a compact and efficient solution for generating stable and adjustable DC voltages.
By incorporating feedback control and filtering components it ensures consistent output voltage levels despite fluctuations in input voltage or load.
With its versatility and reliability, this circuit finds widespread application in electronics from powering sensitive devices to serving as a fundamental component in laboratory equipment and audio systems.