This 3V to 24V variable power supply circuit is like a swiss army knife for powering your electronics.
It is one power supply that can act like many.
You can twist a knob or adjust a setting to change the voltage output anywhere from 3V all the way up to 24V.
This makes it perfect for all sorts of electronics projects where you need different power levels for different devices.
So you can skip the toolbox full of power adapters and just use this one!
Circuit Working:
Parts List:
| Category | Component | Quantity |
|---|---|---|
| Resistors | 3k | 1 |
| 0.3Ω 5W | 1 | |
| 1k | 1 | |
| Potentiometer | 10k | 1 |
| Capacitors | Electrolytic 2200µF 40V | 1 |
| Electrolytic 100µF 25V | 1 | |
| Semiconductors | IC LM1558 | 1 |
| Transistors | 2N3055 | 1 |
| 2N3053 | 1 | |
| 2N3904 | 2 | |
| Diode | 1N914 | 1 |
| Bridge rectifier | 6A4 | 4 |
| Zener | 6.2V | 1 |
| Selector switch | 1 | |
| Fuse | 2A | 1 |
| Transformer | 12-0-12V | 1 |
This variable regulated power supply can adjust its output from 3 to 25V with a current limit of 2 amps, which can be increased to 3 amps or more by using a smaller current sense resistor 0.3 ohm.
The 2N3055 and 2N3053 transistors must be mounted on suitable heat sinks and the current sense resistor should be rated at 3 watts or higher.
Voltage regulation is managed by half of a 1558 or 1458 op amp.
While the 1458 can be substituted in the circuit it is advised to limit the supply voltage to pin 8 to 30 VDC by adding a 6.2V zener or 5.1k resistor in series with pin 8.
The maximum DC supply voltage for the 1458 and 1558 is 36 and 44 respectively.
The power transformer should be capable of the desired current and maintain an input voltage at least 4 volts higher than the desired output, but not exceeding the maximum supply voltage of the op amp under minimal load conditions.
The power transformer shown is a center tapped 25.2V AC 2 amp unit that will provide regulated outputs of 24V at 0.7 amps, 15V at 2 amps or 6V at 3 amps.
The 3 amp output is obtained using the center tap of the transformer with the switch in the 18V position.
All components should be available at radio shack except for the 1558 op amp.
Electrical Characteristic of IC LM1558
| Parameter | Conditions | LM1558 | Units |
|---|---|---|---|
| Input Offset Voltage | TA = 25°C, RS ≤ 10 kΩ | 1.0 | mV |
| 5.0 | |||
| Input Offset Current | TA = 25°C | 80 | nA |
| 200 | |||
| Input Bias Current | TA = 25°C | 200 | nA |
| 500 | |||
| Input Resistance | TA = 25°C | 0.3 | MΩ |
| 1.0 | |||
| Supply Current Both Amplifiers | TA = 25°C, VS = ±15V | 3.0 | mA |
| 5.0 | |||
| Large Signal Voltage Gain | TA = 25°C, VS = ±15V, VOUT = ±10V, RL ≥ 2 kΩ | 50 | V/mV |
| 160 | |||
| Input Offset Voltage | RS ≤ 10 kΩ | mV | |
| Input Offset Current | nA | ||
| Input Bias Current | μA | ||
| Large Signal Voltage Gain | VS = ±15V, VOUT = ±10V, RL ≥ kΩ | 25 | V/mV |
| Output Voltage Swing | VS = ±15V, RL = 10 kΩ | ±12 | V |
| ±14 | |||
| RL = 2 kΩ | ±10 | ||
| ±13 |
How to Build:
To build a Simple 3V to 24V Variable Power Supply Circuit you need to follow the below mentioned connection steps:
Mount the Transistors:
- Mount the 2N3055 and 2N3053 transistors on suitable heat sinks.
Connect the Current Sense Resistor:
- Connect the 0.3 ohm current sense resistor as shown in the circuit diagram.
Set Up the Voltage Regulation:
- Use half of the 1458 or 1558 op amp for voltage regulation.
- Limit the supply voltage to pin 8 of the op amp to 30 VDC using a 6.2V zener diode or 5.1k resistor in series with pin 8.
Use the Power Transformer:
- Use a center tapped 25.2V AC 2A power transformer.
- This will provide regulated outputs of 24V at 0.7A, 15V at 2A, or 6V at 3A.
- The 3A output is obtained using the center tap of the transformer with the switch in the 18V position.
Connect the Components:
- Connect all the components as per the circuit diagram ensuring proper insulation and secure connections.
Test the Circuit:
- Insert the appropriate components and test the circuit by adjusting the voltage and current to verify that it operates as expected.
Final Adjustments:
- Make any necessary adjustments to the component values or connections to optimize the performance of the power supply.
Note:
- It’s essential to follow standard safety practices when working with electronics such as soldering in a well ventilated area and avoiding short circuits.
Conclusion:
To conclude, a 3V to 24V variable power supply circuit is a versatile electronic circuit that can deliver a variable output voltage ranging from 3V to 24V.
This circuit is commonly used in various electronics projects where a flexible and adjustable power supply is required.
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