In the case when a device with a low current consumption requires a constant stable voltage, the transformerless power supply finds its practical application. Having some drawbacks, this power supply is widely used in electronics and radio engineering.
Scope, advantages and disadvantages
Power supplies for many electronic devices are based on transformerless boards. Such power supplies are characterized by high efficiency, small dimensions and weight. They are the most reliable since they do not have winding coils. The area of application of the transformerless power supply is low-power equipment such as chargers, burglar alarm sensors, household lamp switches based on motion sensors and other industrial and radio structures.
The transformerless power supply is not afraid of output short circuits and mains voltage drops. Such a power supply unit works silently, since it is devoid of a transformer, and is quite stable. It is easy to repeat as it consists of a minimum number of parts used. But the main advantage of the transformerless power supply circuit is that the output current rating can be adjusted by self-selection of the required capacitor capacity.
A significant drawback of transformerless power supplies is impulse noise, which negatively affects the neighboring circuits of the device. Therefore, each such power supply is thoroughly tested for electromagnetic compatibility with other equipment. In addition, this power supply does not have a mains galvanic isolation from the supply voltage, which requires extremely careful observance of safety measures while working with this equipment.
Operating principle
Transformerless power supplies are designed to stabilize voltage with a low output current, providing sufficient power for self-contained low-power devices.
When the transformerless power supply is disconnected from the input AC mains, the input capacitor is discharged by means of a parallel-connected input resistor. This happens so that the power supply does not shock a person by accidentally touching the input contacts. On subsequent switching on, an alternating voltage of the network of 220 Volts is supplied and extinguished by a capacitor through a resistor, then, being straightened by a diode bridge, it is fed to a zener diode. Then, after smoothing the ripples and stabilizing with capacitors, the required stabilizing voltage of 12 volts is obtained at the output of the power supply. Thus, it is difficult to overestimate the role and importance of transformerless power supplies.
