Low voltage load power regulation. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Regulators of current, voltage, power
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Often there is a need to control the power (effective voltage value) of a low-voltage load powered by a conventional mains through a step-down transformer. Examples of such loads are DC brushed motors, low voltage soldering irons, incandescent lamps, etc.
DC commutator motors are the most widely used in everyday life. Miniature motors are also used in amateur radio practice; for example, small-sized electric drills are made on their basis. Most often, such devices are powered from the AC mains through a step-down transformer and a rectifier (see diagram).
In practice, it often becomes necessary to control the speed of the motor shaft. Traditional methods of changing the supply voltage using adjustable DC stabilizers, thyristor or triac regulators and other devices that are connected between the rectifier and the motor are of very limited use, since the control unit turns out to be much more complicated than the power unit itself.
However, there is a very simple way to solve this problem. Its essence lies in the fact that the network transformer is connected to the network through a triac power regulator. It should be emphasized that it is a triac (or a two-half-wave iodine thyristor) regulator that is needed, and in no case should a single-half-wave thyristor be used - in this case, most likely, the transformer and the thyristor regulator itself will burn out. Since the current in the primary winding of the transformer is approximately k (transformation ratio) times less than the current in the secondary, the power losses in the regulator itself are small and a "normal" regulator with a permissible current of 0,5 ... 1 A can be used to control quite powerful motors.
Since the loaded transformer is almost purely active resistance, the operation of the triac controller for such a load has no special features. 12, p. 1). Reliable motor control with the help of a triac controller was also ensured with half-wave rectification (turning off one of the diodes).
Similarly, you can control other low-voltage loads - soldering irons, incandescent lamps, etc. The power node is simplified, since the rectifier becomes unnecessary.
Author: D.Turchinsky, Moscow
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