If you are beginners who want to use the simple variable power supply 0-30V 2A. This circuit is best for you. Because it has a few parts,small,and cheapest than others circuit that same power. The features of this handset is 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
In Figure 1 is circuit diagram,
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.
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 36V.
R2-100ohms and ZD1-30V are connected together as the 30V steady DC regulators.
The variable resistors VR1 is used to adjustable the output voltage between 0V to 30V, that have transistors Q1,Q2 increase the output current up to 2A. Also, there are the short-Circuit protection include Q3,R3.
How to 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. The soldering the legs of transistors and diodes we should uses the 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 get current from C1 that does not discharge fully.
If you want to stop LED immediately, 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
If need to used the dual power supply (Positive Ground and Negative terminal) For testing amplifier OCL.
We change the rectifier section to new, from 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
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
R2________100 ohms____0.5W resistor
R3________0.3 ohms 10W resistor.
Bench variable power supply 0-30V
Today I seeks variable power supply circuit come to deposit again. Which be the circuit that use base equipment, build not difficult follow the circuit can fine volt get 0-30V , give current get about 1-2A depend on transformer at you choose to use. The prominent point of the circuit use transistor join a pin BE replace Zener Diode. Then get around problems about seek buy Zener voltage that can’t want. By transistor at use 2N3638 numbers or the number replaces. For transistor output use 2N3055 durable numbers current not exceed 2A. For other detail , request friends , see in the circuit better.