Adjustable Voltage, Current Power Supply Circuit Using Transistor 2N3055

This post shows you how to build a powerful adjustable power supply circuit.

This circuit lets you change both the voltage and amperage it provides, making it super versatile for many electronics projects.

It uses a common transistor 2N3055 and other basic parts.

Building circuits with high voltage can be dangerous.

Only do this with adult supervision.

What is a Adjustable Voltage, Current Power Supply Circuit:

An electrical circuit that offers a changeable output voltage and permits control over the output current supplied to a connected load is known as an adjustable voltage, current power supply circuit.

In electronics labs, workshops and testing facilities where power settings need to be flexible for various experiments and applications, this kind of power supply is frequently utilized.

Circuit Working:

Parts List:

The variable workbench power supply circuit explained in this article not only incorporates a continuously adjustable voltage control but also features variable current control offering overload protection.

How it operates upon closer examination of this 2N3055 based variable voltage current power supply circuit utilizing the 2N3055 transistor, it becomes apparent that it functions as an ordinary stabilized power supply circuit.

Nevertheless, it efficiently delivers the specified features.

Voltage adjustments are achieved by utilizing the preset P2 in a feedback configuration involving components D1, R7, T2 and P2.

The incorporation of D1 ensures that the voltage can be reduced to as low as 0.6V, corresponding to the forward voltage drop of the diode.

If a specific minimum value is required the diode can be substituted with a zener diode having the specified value.

Consequently, in this variable power supply circuit utilizing the 2N3055 transistor and a 0 to 40V transformer the output ranges from 0.6 to a maximum of 40V a highly practical range.

To implement the current control feature, T3 along with P1, R5 and R4 comes into play.

The value of R4 plays a crucial role in determining the maximum allowable output current.

P1 is adjusted to select the maximum range within the values marked or identified by resistor R4.

If there are any uncertainties regarding this variable voltage and current power supply circuit using the 2N3055 transistor feel free to ask questions in the comments below.

Formulas:

Here are some general formulas that are relevant to adjustable voltage regulator circuits:

Voltage Divider R2 and R3:

The voltage at the transistors base Vb may be computed using the following formula if R2 and R3 form a voltage divider:

Vb = (R3 / (R2 + R3)) * Vin

where,

• Vb is the voltage at the base of the transistor
• R2 and R3 are the resistor values in the voltage divider
• Vin is the input voltage

2. Formulas involved in designing a series pass transistor voltage regulator circuit:

Voltage Output Vout:

This is the regulated voltage that the load will get from the circuit.

Usually, its a set amount determined by the specifications of your program.

Voltage input Vin:

This is the source of uncontrolled voltage that powers the circuit.

A battery, wall adaptor or other source may provide the DC voltage.

Dropout Voltage Vdropout:

This is the lowest voltage differential Vin – Vout needed for the transistor to function properly in the active zone and efficiently control the output voltage.

The biasing strategy and transistor properties determine the dropout voltage.

The minimum Vce (collector emitter voltage) for saturation mode is usually specified in datasheets and can be used as a dropout voltage reference.

Current at Load Iout:

This is the maximum current that the load can get from the circuit.

The current requirements of the gadgets you are powering must be taken into account.

Selecting Transistors:

The selection of a transistor is influenced by things like:

Output Voltage and Current: The voltage rating of the transistor must be more than the output voltage, and its current rating must be greater than the load current.

Power Dissipation: The transistor will lose power as a result of the current flowing through it Iout and the voltage differential between its collector and emitter Vce.

A transistor that can withstand this power dissipation without overheating must be your choice.

Here is a formula to determine the power dissipation:

P = V_ce * I_out

Transistor heat concerns and maximum power dissipation are outlined in datasheets.

Rbase, or the biasing resistor:

This resistor controls the transistors base current (Ib), which in turn regulates the collector current I_out.

The required collector current, the gain (β or hFE) of the transistor, and the voltage difference between the base emitter voltage V_be of the transistor and the voltage reference (often the input voltage) are used to compute the value of R_base.

Here is a simplified formula (assuming fixed β):

R_base = (V_in – V_be) / (β * I_out)

Note:

Recall that the usual Vbe of silicon transistors is between 0.6 and 0.7V.

The transistor datasheet contains the β values.

This is a simplified formula, for accurate design more intricate calculations involving considerations of transistor saturation and changes in β may be required.

How to Build:

Building a variable power supply circuit using the 2N3055 transistor involves several process.

Circuit Assembly:

Transformer and Rectification:

• Connect the primary side of the transformer to the mains power source.
• Connect the secondary side to a bridge rectifier to convert AC to DC.

Stabilization Circuit Voltage Control:

• Connect the emitter of T2 to the junction of R7 and P2.
• Connect the base of T2 to the wiper of P2 and the collector to the positive supply.
• Connect D1 in parallel with P2 with the cathode towards the base of T2.
• Connect R7 between the collector of T2 and the base of T2.

Variable Voltage Adjustment:

• Connect the output of the stabilization circuit to the base of the 2N3055 transistor.
• Connect the emitter of the 2N3055 to the negative supply.
• Connect the collector of the 2N3055 to the load.

Current Control:

• Connect P1, R4 and R5 in series and connect this series to the collector of T3.
• Connect the junction of R4 and R5 to the base of T3.
• Connect the emitter of T3 to the emitter of the 2N3055 transistor.
• Connect the wiper of P1 to the base of T3.

Output Load:

• Connect the load (your device) between the collector of the 2N3055 transistor and the positive supply

Heat Sink:

• Attach a suitable heat sink to the 2N3055 transistor to dissipate heat generated during operation.

Power Up:

• Power up the circuit gradually while monitoring the output voltage and current using a multimeter.

Conclusion:

Remember to double check your connections against the circuit diagram and, datasheets for the components you are using.

Take precautions to avoid short circuits and ensure the proper handling of electronic components.

If you are not confident in your ability to build this circuit consider seeking assistance from someone with experience in electronics.

References:

2N3055 Power Supply