Sometimes it is necessary for a lamp to smoothly flare up and go out, or for an electric motor to start smoothly and stop smoothly. For DC loads, such a device can be made very simply with just one transistor. This will be a powerful switch that can switch currents up to 10 A at a voltage of 6-25 Volts.
Will need
Single transistor circuit
The scheme is very simple. When the switch contacts close, current will flow through resistor R1 and begin to charge the capacitor. As a result, the transistor will begin to open smoothly. As soon as the contacts open, the capacitor will begin to smoothly discharge through resistor R2 and the transistor will begin to close.
The transistor begins to heat up only at the moment of opening and closing, as it takes over the control power. As soon as it is completely open or closed, it produces virtually no heat.
Manufacturing of a soft start and stop device
We fix the transistor and tin the output. Solder a 4.7 MΩ resistor to the gate and source of the transistor.
We solder the capacitor to the gate and drain through a jumper made of a piece of wire.
We solder a circuit from a series connection of a switch with a 5.6 MΩ resistor to the gate and source.
We connect the wires to the drain and source of the transistor.
Device test
If you connect a 12-volt incandescent lamp to the circuit, then using the switch you can very smoothly turn the light bulb on and off.
The circuit also works great with DC motors.
The motor shaft is smoothly started and stopped.
