30V 10A Variable Bench Power Supply
Presented here is a circuit for 30V 10A variable bench power supply that offers variable voltage and current adjustment.
Power supply is based around a LM723 voltage regulator chip and has current limiting. I often end up with the power
clips shorting out on the bench and with no problems. I have had this circuit in use now for over 20 years and has never
let me down and is one of the most handiest gadgets i have built. The 2N3055 transistors are a well proven high current
transistor. More 2N3055 transistors can be connected together for more output current. The transistors will need to be
mounted on a good size heatsink.
The bridge rectifier can also be mounted on the heatsink to.
For this reason i mount them off the board and wire to them.
The capacitor bank on the input side can be changed to a single large cap if you have one suitable.
The 5 watt resistors will run rather hot under high load and need to be mounted with air flow around them.
I have often soldered them direct to the pin of the transistors with the other leg connected together and wired back to the
board.
When purchasing the 2N3055 transistors ask for them to be all the same batch number as this will help eliminate internal
differences.
The pot values shown might need to be changed to allow adjustment over the desired voltage range and current limiting
range. A test with the output leads shorted together will soon show max current settable range.
A suitable transformer for the amps required will be needed. It is a simple circuit with a hand full of components.
The only need for a pcb is for the LM723 and the 3 small resistors and 2 caps. The rest is mounted to the heatsink or front panel
and wire connected.
Maximum input voltage is 40 Volts.
See LM723 data sheet for more details.
30 AMP POWER SUPPLY
Description:
A modification to the 12V 30 Amp power supply. This version uses an LM317 to provide a variable 1.5 to 37 Volt
regulated output with currents
nts up to 30 Amps.
Notes
I wanted an adjustable power supplyply from 1.5 volts to 37 volts, based on the LM317 voltage regulator chip. Simple to
remove the 12 volt regulator chip and add the LM317 chip and a 240 resistor, a 10k pot and a 1N4007 diode. Just as easy
to insert any of the other voltage chips as well.
I used an old computer tower to house my project, used the heatsinks from the computer power supply for the power
transistors. The heat sink for the LM317 came from an old TV, and the heat sink and fan for the bridged rectifier came
from the old computor processer.
rocesser. I found the transformer at a flea market.
Also added was a small transformer from an old radio. Rated at 14 volts and small amps.This transformer powers two 12
volt regulator chips wired together on the same heatsink. Wired together there output is 12 volts and 3 amps. This is
power for 2 fans and power for the digital volt meter and amp meter. The volt meter is powered at 5 volts, so another 5
volt chip was added on another circuit board. Digital amp meters use a shunt to measure the amperage, and the power
supply needs to be isolated, easy enough, just use an isolation chip designed for this purpose. Also I used 10 amp output
jacks, plus 10-24 bolts with wing nuts. The bolts are for 10 to 30 amps.
Here in the USA, we use 110 volt mains and 220 volt mains. The transformer I found can be wired for eithor input, and
can can be wired as 16 volt or 32 volt output. 16 volt AC through the bridged rectifier and into the 47,000uf capacitor,
comes out as 19 volts. This is caused by the voltage ripple peak into the capacitor. This caused a problem because the 32
volt AC input comes out as 44 volt DC, and the LM317 chip is listed as 40 volt maximum. So currently I am using the 16
volt AC output from the transformer. After some experiments I plan to try the 44 volt DC and see if the LM317 can
handle it.
