Circuit Adjustable Power 3A
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.
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.
Consider that the heat resistance of a TO-3 package is 1.5oC/W and the maximum allowable temperature is 150oC. If a heatsink is used with a heat resistance of 1.5oC/W, when the total heat resistance is 4oC/W. At 30 watts dissipation and 25oC outside temperature, the resulting internal IC temperature is 145oC. Once this dissipation level is reached, the internal protection activates shutting down the IC.