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Simple Voltage regulator using 2N3055

This is a simple voltage regulator using 2N3055. Here is 12V 1A linear regulator using a transistor and Zener diode. It is a series voltage regulator because the load current passes through the series transistor. As the circuit diagram below, The input terminal wants an unregulated DC supply,15V to 20V. Then, the regulated voltage will come out to the load.

voltage regulator using 2N3055


12V 1A linear voltage regulator using 2n3055 transistor and Zener diode

To begin with, An electrical current flows through the resistor-R1 to limits current to the Zener diode. So it provides the reference voltage.
In the same, the base voltage of transistor-Q1 is also a constant.

When ZD1 is 12V, the base voltage is also the 12 volts.

If we set the transistor in this form. The output voltage is the same as the Zener diode voltage. And we always call this that emitter follower. In practice, the voltage of output is lower than ZD1. Because when a transistor is working. It needs to has a base-emitter voltage.

  • VBE = Base-Emitter voltage
  • VZD = Zener diode voltage
  • Vout = Output voltage

Vout = VZD – VBE
VBe = 0.6V
Vout = 12V – 0.6V = 11.4V


This voltage is still suitable for many loads using the 12V supply such as a receiver radios.

Since it is a power supply that regulates a certain power output.

In the circuit, the transistor has a proper gain and changing of VBE help it.

  • When a load use more current. In general, the output voltage is low down. But the base-emitter voltage rises up, transistor Q1 works more. So it keeps the output voltage to be a constant level.
  • Then, if load use less current. The output voltage increase. But the output is still a fixed voltage. Because the voltage of Base-emitter less, transistor Q1 works less too.

The advantage of this circuit, we can use a tiny current to Zener diode and base of a transistor. Thus, it has a much more stabilized output.

The function of Others components

  • C1 is a smoothing capacitor at an input.
  • C2 keeps the reference voltage to be stable better.
  • C3 is a 0.047uF decoupler capacitor to filter out the transient noise.
  • R1 increases the stability of the load circuit
  • Do you know what is transient noise?
    The power supply has a stray magnetic field. The circuit will induct them into the transient noise. The transistor-2N3055 can power load current up to 2A. But it is so hot. It so needs a proper heatsink.

Return to look: Transistor voltage regulator

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