This post talks about how to make one circuit for high current power supply using one chip called LM7805.
This chip take big voltage and make it stable 5V to give power to devices.
But normal LM7805 give only small current.
In this circuit we use LM7805 to give more power for devices which need little more current.
But this circuit use high voltage, so it little dangerous.
Better one expert electrician should do the work and always do this with one adult watching.
New people or beginners should not try this project.
Circuit Working:
Parts List:
| Component | Quantity |
|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | |
| 6.8Ω | 1 |
| 10Ω | 1 |
| 0.22Ω 3W | 1 |
| 150Ω | 1 |
| Capacitors | |
| Ceramic 100nF | 2 |
| Semiconductors | |
| IC 7805 | 1 |
| Transistor BD240 | 1 |
| Transistor 2N2955 | 1 |
Voltage regulator ICs with 3 pins like LM7805 and LM7812 very good to use in voltage regulator circuits.
But if we want more current like up to 3A than we need to add one more transistor it is called T2 in this diagram.
Old design have big problem when short circuit happen it gives too much heat.
But in this new circuit that problem is fixed.
This new design use smart electronics to stop too much current when short circuit happen so it does not get too hot.
When testing this circuit output is short but only 0.5A current generates, so no overheating happen.
In this DC voltage regulator circuit T1 work like current limiter.
If voltage on R2 and R3 go more than around 0.6 to 0.7 volts than T1 turn ON and stop current going to T2.
How much voltage needed for short circuit protection depend on R2 and R3 together.
Also R3 and R4 make voltage divider for T2.
Formula:
Before trying high current power supply using IC 7805 we must check if 7805 can handle needed current without getting too hot.
IC 7805 is normal linear voltage regulator.
It gives fixed 5V from higher voltage.
Formula and things to remember:
Input Voltage Choose:
Input voltage (Vin) must be more than output 5V plus dropout voltage of 7805.
Dropout voltage usually between 1V to 2V.
It depend on how much current and which 7805 IC one uses.
Current Guess:
See how much current the circuit take from 5V output which is max current (Iout).
Check IC 7805 can handle this current not more than its limit and not become too hot.
Power Loss:
Heat will be released by the IC 7805 which is as follows:
Pdiss = (Vin −5V) * Iout
If there is a considerable amount of power dissipation than 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.
Use the heat sinks maximum power dissipation (Pdiss) and thermal resistance to calculate the required heat sink size.
Example Calculation:
Suppose we need +5V power and it give up to 3A current
- Vin(input voltage) = 12V (from a transformer).
- Vout(output voltage) = 5V.
- Iout(output current) = 3A.
Calculate power dissipation:
Pdiss = (12V − 5V) * 3A = 21W
That mean IC 7805 will lose around 21W power as heat.
To keep IC cool and safe we need big heat sink with low thermal resistance.
By using this calculation and thinking we can build strong high current power supply using 7805.
One can change parts and values as per its voltage and current need.
How to Build:
To build a High Current IC 7805 Voltage Regulator Power Supply Circuit follow the below mentioned easy steps for connections:
Layout Design:
- First plan where parts go on breadboard.
- If want to make it permanent design PCB design.
Connect Voltage Regulator IC:
- Put LM7805 or LM7812 on board.
- Connect power supply to input pin, ground to ground pin.
- Connect unregulated voltage to input pin.
- Connect output pin to the load (device the power is needed).
Add Complementary Transistor T2:
- Place transistor T2 on board.
- Connect collector of T2 to output pin of voltage regulator.
- Connect emitter of T2 to ground.
- Connect base of T2 to correct part of circuit.
Add Resistors:
- Place resistors R1, R2, R3 and R4 on board as shown in circuit diagram.
- Connect them in correct way like in schematic.
Connect the Circuit:
- As shown in the schematic diagram connect all the components with wires or traces.
- Verify that the resistors, transistor and voltage regulator are all connected correctly.
Adding a stability capacitor is optional.
- For a better outcome place a capacitor between the voltage regulators input and output pins if necessary.
Test the Circuit:
- Switch ON the circuit.
- One should check if voltage output is correct like 5V.
- To test short circuit protection and ensure that the current remains safe try shorting the output.
Adjustments:
- If output not perfect change resistor values or other parts to fix.
Finalize and Secure:
- If all working good make connections strong and fix parts in place.
- If want it permanent solder parts on PCB.
Note:
- By doing all above steps we can make voltage regulator circuit with short circuit protection.
- Be careful while working with electronics especially power supply and high current.
Conclusion:
In end this high current IC 7805 voltage regulator circuit help normal LM 7805 give more current for big loads.
This circuit give stable 5V output even when load is heavy because it use extra transistors, cooling parts and some small capacitors for steady work.
If one builds it carefully and test good it will work nice and strong for devices that need more current.