So here we are, now we will see a very easy adjustable voltage power supply circuit which also has regulation, and guess what? We only need one transistor for making it. That is why this design is so good and useful, mainly for new guys in electronics who are still learning but want to build useful stuff.
Main Features
Now this power supply we are talking about, it has one super important thing – adjustable voltage. That is what every electronics guy wants, right? But wait, making one such thing quickly with just a few parts, that looks kind of hard.
But no, do not worry because we will now show one such circuit that works and the best part is, you can just take some random parts from your junk box and make it fast, using only one transistor.
This one-transistor regulated power supply is very easy. Just take a copper-laminate board and assemble everything. It will take less than an hour, that is all.
All parts are placed exactly as shown in the given diagram. You just need to cut the copper strips to fix the components in place.
And here is something cool – the board itself acts like a heat-sink. The wiring? We use enamelled wires to connect the parts. The transistor? We bolt it straight to the board and guess what? That helps in cooling it down.
Circuit Operation
So what do we use as the power source? Nothing fancy! Just grab some old batteries – those big C and D size ones or even those big lantern batteries. That is why we do not need diodes or big capacitors here. Take a bunch of these old batteries and connect them together then boom – you get 12V to 14V, that is enough.
Now the power supply output is controlled using a 10V zener setup. How? We take a BC547 transistor and use its base-emitter junction in reverse bias. That gives us around 8.2V. Then, we add a red LED which gives another 1.7V. Together we get about 10V regulation. Simple!
With this setup we can get an output voltage between 0V to 9V, and it can supply up to 500mA. But hold on, this depends on how fresh or dead the batteries are.
If the batteries are fresh then the output will be strong. If they are weak, then the circuit will still work but with less power.
There is a 10K potentiometer that we turn to adjust the output voltage. And when we do that, then the LED circuit also turns ON.
One great thing about this circuit – it is made in such a way that it can squeeze out every last bit of energy from old batteries before they are completely useless. That is smart right?
Circuit Diagram
How We Build This Simple Power Supply
So now we are going to see how we can put together this circuit using super simple steps. No complicated things. Just basic work. We do not need big tools. Only a soldering iron wire cutter and if we need to drill something then we use a small drill. That is all.
Step 1: First We Collect All the Parts
Now before we start we need all the things right. So we first gather all the required parts. What are they. Here see below.
One BC547 transistor – This is a small transistor that will help control the voltage.
One TIP122 transistor – This is the big transistor that will actually supply the power.
One 10K potentiometer – This is a small turning knob that we will rotate to change the voltage.
One 10V zener diode – This tiny thing will fix the voltage regulation.
One Red LED – This is just a small light to show us that the circuit is running.
One 1K resistor – This will make sure the transistor does not get too much current.
Some wires and a board – To connect all the parts and hold them in place.
Okay now once we have all these parts then we can start making the circuit.
Step 2: Now We Get the Board Ready
We take a small copper-laminate board. If the board has copper strips then we first cut them properly. Why. Because we do not want them to touch each other and make a short circuit. If the board is plain then no problem. We just solder everything directly on it.
Step 3: We Start Placing the Parts
Now we take all the parts one by one and start fixing them on the board.
First we place the TIP122 transistor – This one is big so we keep some space for it. The metal backside of this transistor must touch the board. Why. Because the board itself will act as a heatsink and cool it down.
Then we place the BC547 transistor – This is a small transistor. We put it near the TIP122. Its legs must be in the right positions as we see in the circuit diagram.
Next we fix the LED – The LED has two legs. One long and one short. The long leg is positive and the short leg is negative. So we place it correctly.
Now we connect the zener diode – This tiny diode will go between the base and emitter of the BC547 transistor. But careful. We place it in reverse bias.
Put the 1K resistor – This one goes from the 12V input to the base of the TIP122 transistor.
Now we place the 10K potentiometer – This small adjustable resistor has three legs. The middle leg goes to the base of BC547 and the other two legs go to 0V and 10V.
Step 4: We Do the Wiring
Okay now all parts are in place so we take thin enamelled wires and start making the connections.
Connect the collector of BC547 to the negative side of the LED.
Connect the emitter of BC547 to ground 0V.
Connect the zener diode in reverse bias between the base and emitter of BC547.
Connect the 1K resistor from 12V to the base of TIP122.
Connect the output terminals at the emitter of TIP122. This is where we will get 0V to 9V output.
Bolt the TIP122 transistor to the board – This is important. Because the board will help cool it down.
Step 5: Now We Power It and See If It Works
So now everything is connected but will it work. Let us check.
We take an old battery pack 12V to 14V and connect it to the circuit.
If everything is done properly then the LED should glow.
Now we turn the potentiometer slowly and if everything is correct then we must see the output voltage changing from 0V to 9V.
If we connect a small load like a DC motor or a lamp then it should run as per the voltage setting.
That is it. We have now built a simple working adjustable power supply using just a few small parts and a single main transistor.
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