This article explains how to build a power supply circuit using a special chip called an LM 7805.
This chip normally takes a higher voltage and turns it into a steady 5V for powering electronics.
However, a regular LM 7805 can only provide a small amount of power current.
This circuit shows you a way to use the LM 7805 to provide a bit more power for things that need it.
This circuits is built under high voltage which can be dangerous.
Do this under adult supervision and a qualified electrician should install it in your home.
This project is not recommended for beginners.
Circuit Working:
Parts List:
| Component | Quantity | Specifications |
|---|---|---|
| Resistors | ||
| 6.8Ω | 1 | 1/4 watt |
| 10Ω | 1 | 1/4 watt |
| 0.22Ω | 1 | 3W |
| 150Ω | 1 | 1W |
| Capacitors | ||
| Ceramic 100nF | 2 | |
| Semiconductors | ||
| IC 7805 | 1 | |
| Transistors | ||
| BD240 | 2 | |
| 2N2955 | 2 |
Voltage regulator integrated circuits ICs with three pins, such as those from the LM7805 and LM7812 series are highly suitable for incorporation into voltage regulator circuits.
To accommodate higher currents, up to 3A it is necessary to introduce an additional complementary transistor, labeled T2 in this schematic.
In traditional designs the occurrence of a short circuit can lead to significant power dissipation issues.
However, this concern is addressed by the voltage regulator design presented in diagram.
This circuit design employs electronic techniques to mitigate current consumption during short circuits, thereby minimizing overheating risks.
In testing this voltage regulator prototype the maximum current observed with the output short circuited was only 0.5 A ensuring no overheating occurred.
Within this DC voltage regulator circuit T1 functions as a current limiter.
When the voltage across R2 and R3 exceeds approximately 0.6 to 0.7V, T1 activates effectively reducing the base current to T2 to zero.
The activation threshold for short circuit protection is determined by the combined voltage across R2 and R3 while the resistances of R3 and R4 create a voltage divider for T2.
Formula:
Make sure the IC 7805 voltage regulator can manage the required current without overheating before designing a high current power supply with it.
A common linear voltage regulator that produces a consistent 5V output from a higher input voltage is the IC 7805.
Formula and Points to remember:
Choice of Input Voltage:
The required output voltage (5V in this example) plus the IC 7805s dropout voltage should be less than the input voltage Vin.
The normal dropout voltage varies between 1 and 2V, contingent upon the provided current and the particular model of the integrated circuit 7805.
Present Estimate:
Find out how much of the 5V output your circuit will use to draw the maximum current Iout.
Verify that the selected IC 7805 model can manage this current without going over its maximum rated current or overheating.
Power Loss:
Heat will be released by the IC 7805 as follows:
Pdiss = (Vin −5V) * Iout
If there is a considerable amount of power dissipation, a heatsink should be used to control it.
Where:
- Vin is the input voltage.
- Vout is the output voltage (fixed at +5V for the IC 7805).
- Iout is the output current.
Determine the necessary heat sink dimensions by utilizing the heat sinks thermal resistance and maximum power dissipation Pdiss.
Example Calculation:
Lets say you need a +5V power supply capable of delivering up to 3A of current:
- Vin(input voltage) = 12V (from a transformer).
- Vout(output voltage) = 5V.
- Iout(output current) = 3A.
Calculate power dissipation:
Pdiss = (12V − 5V) * 3A = 21W
This indicates that 21W of power will be lost by the IC 7805.
To make sure the IC runs within acceptable temperature ranges, you would need a large heat sink with low thermal resistance.
You may use the IC 7805 voltage regulator to construct a reliable high current power supply by employing these calculations and considerations.
Adapt component combinations and values to your unique needs for voltage and current.
How to Build:
To build the High Current IC 7805 Voltage Regulator Power Supply Circuit, following steps are mentioned below:
Layout Design:
- Plan the layout of your circuit on a breadboard or design a PCB layout if you are building a permanent version.
Connect the Voltage Regulator IC:
- Connect the voltage regulator IC LM 7805 or LM 7812 to the power supply and ground.
- Connect the input voltage unregulated to the appropriate pin of the voltage regulator IC.
- Connect the output voltage regulated to the load device.
Add the Complementary Transistor T2:
- Place the complementary transistor T2 on the board.
- Connect the collector terminal of T2 to the output of the voltage regulator IC.
- Connect the emitter terminal of T2 to ground.
- Connect the base terminal of T2 to the appropriate part of the circuit.
Incorporate the Resistors:
- Place resistors R1, R2, R3 and R4 on the board according to the schematic.
- Connect the resistors in the circuit as specified in the design.
Wire the Circuit:
- Connect the components together based on the schematic diagram.
- Ensure proper connections between the voltage regulator complementary transistor, resistors and other components.
Optional Stability Capacitor:
- If necessary, add a stability capacitor between the input and output terminals of the voltage regulator IC for improved performance.
Test the Circuit:
- Power on the circuit and verify that the voltage regulator provides the desired output voltage to the load.
- Test the short circuit protection feature by shorting the output and observing that the current consumption remains within safe limits.
Adjustments:
- Fine tune resistor values or other components as necessary to achieve the desired output voltage and performance.
Finalize and Secure:
- Once the circuit is functioning correctly finalize the connections and secure components in place.
- Consider soldering the components onto a PCB for a more permanent setup if desired.
Note:
By following these steps, you should be able to build a voltage regulator circuit with short circuit protection using the provided schematic and components.
Always exercise caution when working with electronic circuits especially when dealing with power supplies and high currents.
Conclusion:
In conclusion, a high current IC 7805 voltage regulator power supply circuit enhances the current handling capacity of the standard LM 7805 regulator to accommodate higher load currents.
This circuit offers steady 5V output even under heavy loads by integrating external transistors with appropriate heat dissipation techniques and adding stability capacitors.
With careful construction and testing it provides an efficient and reliable solution for applications requiring elevated current regulation capabilities.