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| Variable Power Supply 1.25 to 35V 10A with Transistor D13007 and LM317 |
A Variable Bench Power Supply 1.25V to 35V with 13007 Transistor and LM317: Transforming Scrap into Professional Equipment
Hello, electronics enthusiasts!
If you're an engineer, technician, hobbyist, or simply a "Maker" like me, you probably accumulate scrap components at home or in the laboratory. Among the most common treasures found in computer switching power supplies is a very well-known transistor in the maker world: the 13007.
This transistor, designed for fast switching and with excellent collector current capacity, is perfect for our project today: a high-current bench power supply that will transform those forgotten components into an indispensable tool for your projects.
💡 Expert tip: This project demonstrates how it's possible to reuse components from computer power supplies to create high-quality equipment, saving resources and contributing to sustainability in electronics.
📖 LM317 Voltage Regulator Specifications
The LM317 is a 3-terminal adjustable positive voltage regulator capable of supplying a current of 1.5A over a wide output voltage range of 1.25 to 35 V.
For our bench power supply, however, this maximum current would be limited. This is where the ingenuity of our project comes in: we'll enhance the circuit with two transistors to create a Booster that will multiply the current capacity of the system.
With this modification, we can easily deliver 10 Amperes with variable voltage between 1.25 to 37 Volts, using just two NPN transistors 13007 (or 13009, which supports up to 12A).
| Component | Standard Specification | With Modification |
|---|---|---|
| Maximum Current | 1.5A | 10A |
| Voltage Range | 1.25V - 35V | 1.25V - 37V |
| Additional Component | - | 2x 13007 Transistors |
🔌 Schematic Diagram
The schematic diagram of the electrical circuit is shown in Figure 2, which shows the arrangement of each component and their connections. As you can see, the assembly is quite simple and straightforward, even for beginners in electronics.
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| Fig 2 - Schematic Diagram Variable Power Supply 1.25 to 35V 10A |
⚠️ Important note: When assembling this circuit, pay special attention to the polarity of components, especially diodes and electrolytic capacitors. An incorrect connection can permanently damage the components.
🛠️ Operation
The 13007 transistors (which may have different prefixes like D13007, MJE13007, SDT13007, etc.) are configured in emitter follower mode. This means that the output voltage through the emitters will be equal to the output voltage of the LM317 IC.
When you adjust the potentiometer of the LM317 to a specific voltage, the two power transistors reproduce this same voltage at their emitters. Since the collectors of these transistors are connected in parallel, forming a high-current bridge, they transform the limited capability of the LM317 (maximum of 1.5A) into a power supply capable of delivering much higher current.
✨ Educational analogy: Think of the LM317 as the "brain" that controls the voltage, while the 13007 transistors function as "muscles" that provide the necessary strength to deliver high current. Together, they form an efficient team where each component plays its ideal role.
The final maximum current capacity will depend on both the transistors used and the specification of the transformer of the power supply that will power this circuit.
🌡️ The Vital Importance of the Heat Sink
Thermal dissipation is one of the most critical aspects in this project. The 13007 transistors operating at high currents generate significant heat that, if not properly dissipated, can lead to catastrophic failures. Think of the heat sink as the cooling system of a high-performance engine - without it, overheating is inevitable.
Excessive heat not only reduces the lifespan of the transistors but also affects the stability of the output voltage. For continuous operations above 5A, a robust heat sink with sufficient area and, ideally, forced ventilation is indispensable.
Don't skimp on this component! Investing in a good thermal dissipation system, including quality thermal paste, is the difference between a reliable power supply and a frustrating project. Remember: in power electronics, heat is the number one enemy of your project's longevity.
🧾 Complete Bill of Materials
To build this high-current bench power supply, you will need the following components. We've organized the list clearly to facilitate your purchase or inventory check:
| Component | Specification | Notes |
|---|---|---|
| IC | LM317 | Adjustable voltage regulator |
| T1, T2 | MJE13007 | NPN power transistors |
| D1, D2 | 1N4007 | Rectifier diodes |
| C1 | 4700 uF - 63V | Main filter electrolytic capacitor |
| C2 | 10 uF - 63V | Stabilization electrolytic capacitor |
| C3 | 47 uF - 63V | Output electrolytic capacitor |
| R1 | 220 ohms | Resistor (red, red, brown) |
| R2, R3 | 0.22 ohms - 5W | Power resistors (red, red, gold) |
| P1 | 4.7 k ohms | Linear or logarithmic potentiometer |
| B1, B2 | 2-way terminal blocks | Solderable type for input and output |
| Others | Wires, Solder, etc. | Basic assembly material |
💡 Expert tip: If you can't find the 13007 transistor, you can replace it with the 13009, which supports up to 12A of collector current. This will give you an even greater safety margin for your power supply.
🔧 Couldn't find the 13007 transistor? Don't worry! We offer an exclusive tool for Transistor Substitution by Data Cross-Reference that helps you find compatible alternatives. Just access our substitution tool, enter the transistor code and get a list of direct substitutes and equivalents that will work perfectly in this circuit.
💡 Assembly and Safety Tips
To ensure the correct and safe operation of your bench power supply, follow these important recommendations:
⚠️ Essential Precautions
- Heat dissipation: The 13007 transistors must be mounted on a good heat sink, as they will operate with high currents and generate significant heat. Consider using thermal paste to improve heat transfer.
- Isolation: If the transistors are mounted on the same heat sink, use mica insulators to prevent short circuits between the collectors.
- Ventilation: For continuous operations at high current, consider adding a small fan to assist in cooling the components.
- Adequate transformer: Use a transformer with current capacity compatible with your needs (minimum 10A to take full advantage of the circuit's potential).
🔍 Circuit Testing and Adjustment
After assembling the circuit, follow these steps to test and adjust your power supply:
- Initial check: Before powering on, check all connections, especially the polarity of diodes and electrolytic capacitors.
- No-load test: Connect a multimeter to the output and turn the potentiometer to check if the voltage varies correctly between 1.25V and approximately 37V.
- Load test: Connect a resistive load (such as a lamp or power resistor) and check if the power supply maintains the regulated voltage.
- Temperature monitoring: During testing, monitor the temperature of the transistors and the LM317. If any component heats excessively, turn off immediately and check the connections.
👉 Possible Improvements and Modifications
After building your basic power supply, you can consider these improvements to make it even more versatile:
- Adding voltmeter and ammeter: Install digital meters for direct visualization of output voltage and current.
- Current limiting: Implement an overcurrent protection circuit to protect your projects.
- Polarity reversal protection: Add a diode at the input to protect the circuit against incorrect connections.
- Multiple outputs: Create fixed output terminals (such as 5V and 12V) in addition to the variable output.
❓ Frequently Asked Questions (FAQ)
Can I use other transistors besides the 13007?
Yes! You can use transistors with similar characteristics, such as 13009, 2SC5200 or even TIP35C, as long as they are NPN and support the desired current. Always check the datasheet for compatibility. To facilitate your search, use our tool: Equivalent BJT Transistor by Data Cross-Reference, which will provide compatible alternatives based on the necessary electrical characteristics.
What is the maximum power this power supply can provide?
The maximum power will depend on the output voltage and the transformer used. For example, at 12V with 10A, you would have 120W. Remember that the transistors will need to dissipate the heat resulting from the difference between the input and output voltage.
Is it possible to add current control?
Yes, it's possible to implement a current control circuit, but this will require more complex modifications to the original circuit. There are several online projects that show how to add this functionality.
🔗 Related Content
If you liked this project, you might also be interested in these other articles:
- Adjustable Power Supply 1.25v to 57V, 6 Amps with TIP36C + LM317HV + PCB
- Adjustable Power Supply 1.25v to 33V, 3 Amps with LM350 + PCB
- Stabilized Power Supply 13.8V High Current 10 Amps with PCB
- Adjustable Power Supply 1.2 to 37V High Current 20A with LM317 and TIP35C + PCB
- Switched Power Supply SMPS 13.8V 10A using IR2153 IC and IRF840, with PCB
- Adjustable Power Supply 1.2V to 37V, 6A, Short Circuit Protection with LM317 and TIP36 + PCB
- Symmetrical Adjustable Power Supply 1.25V to 47V 10 Amps with Short Circuit Protection + PCB
👋 Conclusion
With this project, you've transformed simple components into a professional bench power supply, capable of meeting the most demanding needs of your electronic projects. Besides saving money, you've developed practical skills and better understood how power supplies work.
🎉 Challenge for you: After building your power supply, share a photo in the comments or on our social media! We'd love to see your creation and how you personalized the project. If you have difficulty finding any component, remember to use our tool: Equivalent BJT Transistor by Data Cross-Reference, to find compatible alternatives.
Original article published on FVML (Portuguese) – August 12, 2019
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