Discrete Voltage Regulator Circuit using BD680

Introduction

The discrete voltage regulator circuit is a simple yet effective way to regulate and stabilize the output voltage in electronic circuits. By using a BD680 transistor, this circuit can efficiently control the voltage fluctuations and provide a stable power supply to various components or loads.

The BD680 transistor is a widely used, high power transistor that can handle up to 4 amperes of current and has a maximum voltage rating of 80 volts. This makes it suitable for applications requiring higher voltages and currents. When used in a discrete voltage regulator circuit, the BD680 transistor acts as the main component responsible for voltage regulation

This simple electronics project of discrete voltage regulator circuit is designed to maintain a constant output voltage irrespective of variations in the input voltage or changes in the load resistance. This ensures that sensitive electronic components receive a stable voltage, preventing damage caused by voltage spikes or drops.

Discrete Voltage Regulator Circuit Diagram

The circuit diagram provided is quite straightforward, utilizing a small number of components including semiconductors, resistors, a capacitor, and a diode. The output current capability is determined by the output transistor, with the BD680 transistor used here being able to deliver a maximum current of 4 A at a collector-emitter voltage of 10 volts, given sufficient cooling. However, the peak current is 6 A, making it challenging to match with an integrated voltage regulator.

This project can be designed using a few basic components. The circuit diagram of this project is shown below.

**Discrete Voltage Regulator Circuit Diagram**

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Components List of Discrete Voltage Regulator Circuit

Following is the list of all components used in this project:

T3 …. BD680 Transistor x 1
T1 …. BF256A Transistor x 1
T2 …. BC547B Transistor x 1
D1 …. 15V 400mW Diode x 1
C1 …. 100uf Capacitor x 1
R1 …. 1k Resister x 1
R2 …. 10k Resister x 1
R3 …. 22k Resister x 1
P1 …. 1k Potentiometer x 1

Working Explanation of Discrete Voltage Regulator Circuit

The functioning of the circuit itself is uncomplicated. The JFET T1 ensures that Zener diode D1 receives a steady current of approximately 1 mA, maintaining a consistent reference voltage. To achieve a gradual startup, capacitor C1 is connected in parallel with D1, also providing additional buffering and minimizing the impact of noise and disturbances. The circuit typically takes around three seconds to fully start up.

In order to create a voltage regulator, the only extra component required is an output buffer for the reference voltage. This is done through a super-darlington configuration comprising transistors T2 and T3. Although this setup works effectively, one drawback is that the output voltage will be approximately one diode drop lower than the zener voltage. By incorporating preset P1, this can be corrected, albeit at the expense of slightly reduced regulation. Alternatively, if the voltage difference is not critical, P1 can be replaced with a wire bridge. The maximum output voltage achievable is capped at 30 V.

Conclusion of Discrete Voltage Regulator Circuit

In conclusion, the circuit diagram provided is simple and uses a small number of components. The output current capability is determined by the BD680 transistor, but the peak current of 6 A may pose challenges when matching with an integrated voltage regulator. The circuit functions through the JFET T1 and the Zener diode D1 to maintain a steady reference voltage. The startup time is around three seconds. To create a voltage regulator, an output buffer using transistors T2 and T3 is required. However, the output voltage will be slightly lower than the Zener voltage, which can be corrected using preset P1 or a wire bridge. The maximum achievable output voltage is 30 V.

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