Adjustable Voltage, Current Power Supply Circuit using Transistor 2N3055

This Adjustable Voltage, Current Power Supply Circuit using Transistor 2N3055 talks about how to make simple and useful power circuit.

This circuit can change voltage and current so it work for many electronic projects.

It uses one popular transistor called 2N3055 and some other parts.

WARNING: Be careful, High voltage can be very dangerous.

Do this only with adult help or someone who know electricity.

What is a Adjustable Voltage, Current Power Supply Circuit:

A electric circuit that give changeable voltage and also controls current to load is called adjustable voltage current power supply.

In electronics lab, testing place and workshop people use this type power supply when they need different voltage for testing or for research.

Circuit Working:

Parts List:

This article show one circuit for power supply station with both voltage and current control.

We can change voltage all time and also change current which also stops overload so its safe.

If we look close this power supply circuit using transistor 2N3055 work same like normal power circuit.

But it give extra function which is good.

By using preset P2 with parts D1, R7, T2 and again P2 in feedback we can change voltage.

D1 ensures voltage goes low which is almost 0.6V because diode drops voltage.

If we need some minimum voltage use Zener diode instead of normal diode.

So this power circuit with 2N3055 transistor and 0 to 40V transformer can give voltage from 0.6V up to 40V which is very useful.

For current control parts T3, P1, R5 and R4 are used.

R4 mostly decide how much current comes out.

We can change P1 to get many current values based on R4.

If we do not understand or have questions about this circuit with 2N3055 transistor please ask in comment box below.

Formulas:

For circuits with changeable voltage regulator some standard formulas are used.

Voltage divider using R2 and R3:

When R2 and R3 make voltage divider the base voltage of transistor (Vb) is:

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

where:

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

When making circuit with series pass transistor voltage regulator uses these formulas:

1. Output voltage (Vout):

This is voltage that goes to load.

It is fixed value based on what we need.

2. Input voltage (Vin):

This is raw voltage that comes from power source like from battery, adapter etc.

3. Voltage Dropout (Vdropout):

This is the lowest difference between Vin and Vout for transistor to work properly.

If Vin and Vout is too small then transistor does not regulate well.

Dropout depends on transistor specifications and how it is biased.

Check datasheet for minimum Vce i.e. collector-emitter voltage in saturation.

4. Load Current (Iout):

This is max current that circuit can give to load.

We need to know how much current our device needs.

How to choose transistor:

When picking transistor look at:

Output Voltage and Current:

Transistor must handle more voltage and more current than circuit gives to load.

Power Loss:

Transistor loses power due to voltage drop (Vce) and current flow (Iout).

So power loss is:

P = Vce * Iout

Choose transistor that can handle this power.

Check datasheet for max power and if it needs heatsink.

Bias Resistor (Rbase):

This resistor control base current (Ib) which also controls collector current (Iout).

Use this formula for simple one:

Rbase = (Vin – Vbe) / (β * Iout)

where:

• Vin is the input voltage
• Vbe is the base emitter voltage which is usually 0.6 to 0.7V for silicon
• β (or hFE) is the transistor gain for that check the datasheet
• Iout is the output current

Note:

This formula is simple.

Actual design may need to calculate more things like saturation and change in β.

How to Build:

To build a Adjustable Voltage, Current Power Supply Circuit Using Transistor 2N3055 follow the below steps for connections:

Rectifier and Transformer:

• First connect transformer primary side to main AC power.
• Then connect secondary side to bridge rectifier to change AC into DC.

Voltage Control for Stabilization Circuit:

• Connect T2 emitter to place where R7 and P2 meet.
• T2 collector goes to positive power.
• T2 base connects to middle leg wiper of P2.
• Put diode D1 and P2 in parallel with D1 cathode which is going to T2 base.
• Connect R7 between T2 base and collector.

Adjustable Voltage Output:

• Connect base of 2N3055 to output from stabilization circuit.
• Connect 2N3055 emitter to negative power side.
• Load the device connects to 2N3055 collector.

Current Control:

• Put P1, R4 and R5 in one line in series and connect this to T3 collector.
• Join T3 base to point where R4 and R5 meet.
• Connect 2N3055 emitter and T3 emitter together.
• P1 wiper middle leg goes to T3 base.

Connecting Load:

• Connect the load between 2N3055 collector and positive power line.

Heat Sink:

• Connect good heat sink to 2N3055 to keep it cool when working.

Power Up Slowly:

• Use multimeter to check voltage and current.
• Slowly turn up power to test circuit.

Conclusion:

For Adjustable Voltage Current Power Supply Circuit using Transistor 2N3055 always check wiring with circuit diagram and read datasheet of parts.

Be careful with all parts and avoid short circuits.

If not sure how to build circuit better ask for help from someone who knows.

References:

2N3055 Power Supply