If you are looking for a simple and cheap fixed dc source circuit. It is one of the best choice.
See in the circuit below. Why should we use this circuit?
- The constant output of 12 volts, at max output current of 1A.
- The input voltage, you can select both AC (12V to 15V) and DC (15V to 18V)
- It’s flexible. Read more below!
Small Zener diode voltage regulator circuit
How it works
If We need to use a micro preamplifier with a power amplifier. Which it uses a supply 12V 0.5A. We can connect the input terminal to a sec of the transformer.
First, the ACV comes to rectifier bridge, D1 through D4, rectifies the AC into pulsating DC.
Second, the capacitor-C1 will smooth that pulsating DC into a steady DC.
Third, this DC flows through resistor-R1 and Zener diodes-ZD1. The R2 reduce a current for ZD1 until it has a constant voltage at VZ, 12V.
While there is 12V at the base of transistor-Q1. Since it is in a common collector. So the voltage of base(VB) equals the voltage of emitter(VE).
But while It is conducting, the electrical current flows through B-E. There is the voltage across B-E, 0.6V. Thus, the VE or output voltage is reduced to 11.4V.
When the load makes the output of voltage changes. But the gain of Q1 will make the VE to be the constant voltage.
12V 1A linear regulator using transistor and Zener diode
This is 12V 1A linear regulator using transistor and Zener diode. It is a series voltage regulator because the load current passes through the series transistor. As circuit diagram below, The input terminal wants an unregulated DC supply,15V to 20V. Then, the regulated voltage will come out to the load.
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.
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.
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 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 increase the stability of the load circuit
- Do you know what is transient noise?
A 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.
How to build it
Highlights of this circuit are so small in size. See in below the copper PCB layout. You need to print it in 300dpi per inch. Then, solder the components on PCB as layout below.
Actual-size of Single-sided Copper PCB layout
Component layout for the PCB
It is easy, I believe you can do.
Why is it flexible?
Many flexible you should build it.
We can change the output of voltage by ZD1 such as 6V, 9V, 10V. Its power is 1W.
What is least Input voltage? We need to increase input voltage by at least 1.25 times of output. For example, If the output is 15V, The input will equal about DC19V (15V x 1.25) or AC15V.
Important! We change a voltage of C1 (WVDC) to be 2 times of input. For example, the input is 18V, WVDC should be about 35V. The C1 is 470uF 35V Electrolytic capacitor.
However, we not should use the input voltage more than 25V. Because while the circuit is working will too hot. We cannot use the big heatsink. It is not small size, it doesn’t our concept at the beginning.
Some friend does not clear about AC in. In these circuits, you can use them 2 form. As the image below. It is different the place of the power switch and fuse. You can use both forms.
It is important that you have a voltage transformer rating and the output DC voltage.
You need to use 12V 0.5A DC voltage. You should use the secondary coil of the transformer at least 12V. Because when it is converted into DC. The voltage will be about 17V.
From mathematical formulas:
DCV = 1.4V x ACV
For the output current. You should use a transformer at least 0.5A. But 0.75A current is better.
Also, we want you to see the article below they are related.
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