The regulator is designed to control the brightness of a portable luminaire powered by a car on-board network made from a car headlight. The H1 tube is powered by pulse current through a key on a high-power VT1 key FET. The transistor can IRLR2905 switch a load powered by up to 30V at up to 50A.
With a load current of 8A (lamp power 100W), the voltage drop on the open channel is no more than 0.1V, so the power is dissipated at the transistor about 1W, and it does not need a heatsink.
The transistor gate receives pulses generated by a multivibrator on the D1 chip. The brightness of the lamp is regulated by changing the duty cycle of these pulses using resistor R1. The effective voltage across the lamp varies from 11.5V to 0.7V (with a supply voltage of 12V).
The transistor dissipates low power, but with a load current of more than 10 A, it still needs to be installed on a heatsink.
The same regulator can be used to control other loads that are powered by 15V or less, such as a DC commutator motor.
If it is necessary to work at a higher voltage (but not more than 30V), the supply voltage of the chip should be limited by a stabilizer. If this stabilizer gives an output of 5V, the VD4 zener diode can be excluded.
