3A adjustable power supply

aPowerSupply.com — Tue, 24 Jan 2012 12:21:35 +0000

This is a compact adjustable power supply that delivers a stable voltage and currents up to 3 amperes. The circuit is very conventional and its voltage output can be varied from 1.25 volts to 25 volts.
The main module is the LM350 IC which integrates a voltage regulator and a power stage. It also has a built-in overload protection which activates at 30 watts of power dissipation. The voltage output is set by connecting the “adj” pin of the IC to the voltage divider made of R1 and P1. The output voltage can be calculated using the following formula:
1.25V x (1 + P1/R1)
where the P1 value is between 0 and 2.5 KΩ. Capacitor C1 is a common ripple filter while capacitors C2 and C3 improves the regulation. The diodes D1 and D2 serves as protection for the regulator IC when the IC output is turned off. Resistor R1 is 120Ω. This ensures that the minimal load current for the IC (around 3.4mA) is high enough to maintain good performance.

3 Ampere power supply circuit schematic

One thing that is most important in building the electronic circuit: provide adequate heatsink for the LM350 IC. The power dissipation at the IC is very high, around 85 watts.
Consider that the heat resistance of a TO-3 package is 1.5^oC/W and the maximum allowable temperature is 150^oC. If a heatsink is used with a heat resistance of 1.5^oC/W, when the total heat resistance is 4^oC/W. At 30 watts dissipation and 25^oC outside temperature, the resulting internal IC temperature is 145^oC. Once this dissipation level is reached, the internal protection activates shutting down the IC.

Adjustable Power supply PCB

One way to avoid high dissipation levels is to use a lower voltage transformers when needed output voltages are low. To put it simply: if you are using the circuit to supply voltages around 9 volts, do not use a 25 volts transformer but use a lower voltage one instead (e.g. 12 or 15 volts).

Adjustable Voltage Regulator

aPowerSupply.com — Thu, 29 Dec 2011 02:38:37 +0000

This Adjustable Voltage Regulator is made by combining a common 78L05 with an integrated audio amplifier of the type TDA2030, an adjustable voltage regulator can be constructed in a very simple manner that works very well. The output voltage is adjustable up to 20 V, with a maximum current of 3 A. Since the TDA2030 comes complete with a good thermal and short-circuit protection circuit, this adjustable regulator is also very robust.
As illustrated by the schematic, the design of this circuit is characterized by simplicity that is hard to beat. In addition to the two ICs, the regulator contains actually only two potentiometers and a few capacitors.

The adjustment is done by ﬁrst turning potentiometer P1 to maximum (wiper to the side of the 78L05) and subsequently turning trimpot P2 until the desired maximum output voltage is reached. P1 is then used to provide a continuously adjustable voltage between this maximum and nearly zero volts.

At relatively small output currents there are no specific requirements regarding the cooling. However, when the output current exceeds 1 A, or if the input to output voltage difference is quite large, the amplifier IC has to dissipate too much power and a small heatsink is certainly appropriate.

Power supply circuit » Adjustable

3A adjustable power supply

3 Ampere power supply circuit schematic

Adjustable Power supply PCB

Adjustable Voltage Regulator

Adjustable 3 Ampere Voltage Regulator Circuit Diagram