Laboratory power supply 0-30V 0-3A

As one of the basic equipment of every craftsman is an adjustable laboratory source. There are many schemes on the Internet, but everyone has their pros and cons. Some are simple but do not have current regulation, some have everything you need but are difficult to manufacture. This adjustable power supply has something from everything and can be considered „laboratory 0-30V 0-3A“. The resource has a few enhancements that set it apart from all others.

Most sources can be regulated from 1.5 V and more. This source can be regulated directly from scratch. To make this possible, a negative reference voltage (approx. -6V) is used to supply the stabilizer, which is taken from the stabilizer formed by the zener diode DZ1 and the LED diode D7, which is also used as an indication of the switched-on source. LED D9 serves as an indication of current limitation.

In order for the reference stabilizer together with the main rectifier to work properly, it is necessary to draw at least the same current from the main rectifier as from the auxiliary one, otherwise the no-load voltage on capacitor C1 would increase and the source could be damaged. Higher current consumption from the main rectifier is guaranteed by resistors R1 and R2.

The source is adapted for AC power supply from a 230 / 24V mains transformer. A 100W transformer should be used for proper operation and hardness of the power supply. Connect the transformer secondary to terminal block K1. The output voltage is taken from the terminal block K2.

The IO1 stabilizer must be placed on a sufficiently dimensioned heatsink. Potentiometer R5 is used to regulate the output current. Potentiometer R12 is used for coarse adjustment of the output voltage and R13 for fine adjustment.

Circuit diagram:

LM350 circuit

I built this resource in 2015 and it is used regularly to this day. I have 2 of these power supplies incorporated in the plastic box, each works independently, or they can be connected to obtain a symmetrical power supply.

Another useful type is to use a tapped transformer. I used a 24V transformer with a center, in other words 12-0-12V, for the construction of the laboratory power supply. Using a switch, I switch to either 12V or 24V AC power supply input. This is useful when I need voltage in the lower half of the range, so I don’t have to convert such power dissipation into heat. Example: My power supply is set to 5V and I draw 1.5A, so the power consumption is 7.5W. The voltage after rectification is 32.4V, with the same current flowing is 48.6W. I have to turn the difference between the two wattages into heat loss on the heatsink, ie 41.1W. In the case of using 12V AC at the input, after rectification it will be 15.5V, power consumption 23.3W, the difference in this case is 15.8W, which is more than 2x less than in the previous case.

Placement plan:

adjusteble power supply pcb

Printed circuit board:
pcb lm350 toppcb lm350 bottom

Placement plan and PCB are at 1:1 600 dpi (How to print a PCB design can be found in the post How to print PCB design). Real size PCB is 86,3 x 46,7 mm.

Part list:
C14700uF/35V electrolytics
C2, C5100nF ceramic
C3, C4100uF/35V electrolytic
D1-D4, D81N5408
D5, D6, D101N4007
D75mm green LED
D95mm red LED
DZ13,9V Zener diode
R1, R2, R72k7
R51k linear potentiometer
R6, R930k
R8, R10220R
R114k7 (or 2k7)
R12100k linear potentiometer
R135k linear potentiometer
T2, T3BC547
K1, K2screw terminal for PCB, 2 pin, RM 5mm

jlcpcb power supply

The scheme of the laboratory power supply is based on this construction, but it has undergone some changes, mainly in the area of increasing the maximum current:

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