If you are beginners. You want a simple variable power supply. That can give 0-30V 2A output.
This circuit may be best for you. Because it has a few parts, small, and cheapest. Than others circuit that same power.
The features of this handset are the DC voltage continuously from 0-30 volts. And, apply current up to 2 amperes. And can put easily in a large pro box.
How it works
The power supply is a circuit that is easy to understand. Because there are quite clear components.
I like to study it. If you like me. Let’s see. Is it really easy to understand?
See the image below.
This is a Block Diagram of Simple Adjustable Power supply circuit. Let me explain to you how it works step by step.
Unregulated Power supply
It will change AC main into lower DC voltage, about 36V 2A. Almost all of the power supply will use it.
I believe that you have used and understood its work well.
Recommended: Working principle of unregulated power supply
Adjustable Reference Voltage
The electricity is divided into 2 ways.
The first way:
Some little current flows through Adjustable Reference Voltage.
It determines the output voltage level of the output constant.
This circuit consists of Zener diode and Variable resistor.
The Second way:
The most current will flows through the power transistor. It works like a large bridge for higher current through.
And it have the controlled current lead. To control the max output current, 2A.
Read Also: Simple Fixed DC regulator
When the current exceeds 2A. The power transistor is working hard. There is high heat. Until it may be damaged. And also damage other devices.
We should therefore have the overload protection section.
Inside there is the resistor to check higher current and transistor to cut of the contrlled current of power transistor down.
See the Circuit Diagram
First, we apply AC line to the circuit to SW1 on/off to the transformer T1 and fuse F1 to protection circuit when too much power source.
Second, T1 reduce AC voltage 220V into 24V 0 24V.
Then, the current through to both diode D1, D2 to rectifiers to DC voltage.
Next, C1 filter current to DC voltage about 36VDC and 2A max.
There are LED1 to show power on and R1 limit current to a safe value.
Read next: Limiting current using Resistor
Next, the current comes to the regulated section.
The reference voltage
R2-100ohms and ZD1-30V are connected together as the 30V steady DC regulators.
The variable resistors VR1 is used to adjust the output voltage between 0V to 30V.
What is more? the constant voltage will control base of power transistor, below!
There are transistors Q1, Q2 in Darlington mode. To drive or increase the output current up to 2A.
Also, there is the short-Circuit protection include Q3, R3. How it works?
Here is a step by step process.
- First of all, load uses too many currents.
- Second, the voltage across R3 is more than 0.6V and B-E of Q2 too.
- So, Between C-E is like a closed switch. To stop Q1 and Q2 run.
- And C-E of Q2. It is an open switch. The current can via it lower too.
- Thus, the output is low current to protect this circuit.
Note: In my opinion, this overload part is not the best. But better than none.
How it builds
The circuit assembly is very simple Because the devices are less Can assemble down on the perforated board.
While the power transistor Q3 – 2N3055 is working, will hot so we always use a heat sink on it.
Should use low wattage soldering iron does not exceed 30 watts. To soldering the legs of transistors and diodes.
We should use pliers with leg devices Because these devices cannot be very hot.
Adjustment and usage
The prototype works well, have ripple voltage at output lower than 1 mV and the output voltage will drop lower than 0.1 volts
In real usage that although it off, LED power ON will still light up for a moment. Because the LED gets current from C1 that does not discharge fully.
If you want to stop LED immediately. You may move R1 and LED1 to across the secondary of T1.
Then, add the diode-1N4001 series with LED to protects voltage backward which LED may be damaged as Figure 2
We change the rectifier section to new, from a Full-wave into the bridge and use the two secondary coil; 24V 2A.
Then, apply the negative and positive of each channel to the ground as Figure 3
The parts you need
0.25W Resistors, tolerance: 5%
R1: 3.3K, 0.25W resistor
R2: 100 ohms, 0.5W resistor
R3: 0.3 ohms 10W resistor
VR1: 10K Potentiometer
C1: 2,200µF 50V
C2: 220µF 50V
Semiconductors and others
Q2, Q3: 2N3055 Power NPN transistor
Q1: BC548,BC549, 45V 100mA NPN Transistor
D1, D2: 1N5402 3A 100V Diode
D3: 1N4002 1A 100V Diode
ZD1: 30V 1W Zener
T1: 117V/230V AC primary to 24V-0-24V,2A secondary transformer
S1: On-Off toggle switch
F1: 110V/220V, 500mA, slow-blow fuse
Be careful Components pinouts
Some parts of this have different pins. You need to put it in the correct way only!
Hand-picked related articles you may want to read:
- Transistor Variable power supply 1A, 0-30V
- 741 adjustable voltage Power supply regulator
- Cheap DC adjustable 0-30V 2A Laboratory
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