You can control currents up to about 5 A with the indicated components.
The complete circuit is given in figure 1.
Utilities:
• Brightness control of machine or car panel lamps
• Control of heating elements in greenhouses or automotive use
• DC motor speed control
• Control of solenoid actuation force
• Control of motors of robots and mechanical arms and of diverse automatisms.
Constructive Details:
In figure 2 we show a suggestion of printed circuit board.
The power transistor Q1 must be mounted outside the plate on a good heat radiator, especially if the controlled load requires a current greater than 3 A.
The potentiometer P1 must be wire and the high currents of the board must be very wide. The wires for controlled loading and inlet must also have thicknesses compatible with the driven chain.
For smaller currents a lower power transistor such as TIP42 can be used. For this transistor the maximum current controlled will be of the order of 3 A.
Semiconductors:
Q1 - 2N2955 - high power PNP transistor
Q2 - BD135 - medium power NPN transistor
Resistors: (5%)
R1 - 470 ohm x 1 W
R2 - 100 ohm x 2 W
P1 - 1 k ohm - wire potentiometer
Several:
Heat radiator for transistor Q1, printed circuit board, wires, solder, etc.
