Voltage regulators play a crucial role in maintaining stable voltage outputs in various electronic applications. The LM7805, a widely used three-terminal linear voltage regulator, typically provides a fixed 5V output and is limited to a maximum current of about 1A. By adding a current boost circuit, the regulator’s current capacity can be significantly increased. However, in high-current designs, incorporating overcurrent protection becomes essential to safeguard the circuit and connected devices.
This article introduces a modified current-boosting voltage regulator with an overcurrent protection circuit using a 2N6049 transistor and a resistor.
Original Current Boosting Circuit
The basic concept of current boosting in voltage regulators involves using a power transistor to share the load current, as discussed in the current-boosting voltage regulator article. While this design significantly increases the current handling capacity, it lacks overcurrent protection, making it susceptible to damage under fault conditions.
Adding Overcurrent Protection
The enhanced circuit includes an overcurrent protection feature that limits the maximum current supplied to the load. This is achieved by adding a 2N6049 transistor and a current-sensing resistor (Rsc) to the previous design.
Circuit Schematic
Below is the enhanced Voltage Regulator with Currrent Boosting and Overcurrent Protection Circuit Diagram:
Components Used
LM7805: Provides a regulated 5V output.
2N2955 (PNP Transistor): Shares the load current with the LM7805.
1N4007 Diode: Protects the 2N2955 from reverse voltages.
R1 (100Ω): Activates the 2N2955 when the load current exceeds the LM7805’s capability.
2N6049 (NPN Transistor): Acts as the overcurrent protection element.
Rsc: Current-sensing resistor calculated as:
Where Isc is the desired current limit.
How It Works
Normal Operation:
The LM7805 supplies the load until its current limit is reached.
When the load current increases, the voltage drop across R1 activates the 2N2955 transistor, which starts supplying additional current.
Overcurrent Protection:
As the load current increases further, the voltage drop across Rsc rises.
When the voltage across Rsc exceeds 0.7V, the 2N6049 transistor turns on.
The 2N6049 reduces the base drive to the 2N2955, limiting the current supplied to the load.
Circuit Design Considerations
Selecting Rsc: Choose Rsc based on the desired overcurrent threshold. For example, to limit the current to 3A:
Thermal Management: Both the 2N2955 and the 2N6049 must be adequately heat-sinked to handle the thermal load.
Protection Diodes: The 1N4007 diode prevents reverse voltage damage to the 2N2955, ensuring reliability under transient conditions.
Applications
Custom Power Supplies for Arduino: Use this design for creating custom power supplies for Arduino projects that require stable, high-current outputs.
General Voltage Regulation: Extend the capabilities of standard regulators in designs such as those using LM7805 series voltage regulators.
Advanced Voltage Regulation: For detailed designs, explore the op-amp series voltage regulator design.
Simpler Regulators: Consider similar principles in simplest series regulator designs.
Inverter Applications: Adapt this circuit for applications like building an inverter with Arduino or inverters using a 555 timer.
Conclusion
The addition of overcurrent protection enhances the utility and safety of the current-boosted voltage regulator. By incorporating the 2N6049 transistor and a current-sensing resistor, this design ensures that the circuit operates reliably even under high-load conditions. Such robust designs are indispensable for powering high-current applications and provide a foundation for exploring advanced voltage regulation techniques. For further insights, check out related resources on designing power supply circuits for various applications.