The electronic module in the washing machine provides control, execution of commands and programs. Any electronic device needs an electrical supply, but this supply must be prepared for each node. To ensure these goals, power supplies are used in the modules, the name is not entirely correct, more precisely, it will be a mains voltage converter.
The overwhelming majority of modern control modules, and other electronic equipment, use switching power supplies. Due to their economy and high efficiency, these solutions have practically supplanted devices on a network transformer. Only a few manufacturers still prefer reliable, albeit bulky, transformers.
A switching power supply is called so because it generates a high-frequency pulse voltage that is easier to transform, that is, to lower.
The mains voltage of 220 volts comes to the power source of the module, this voltage is suitable for powering many machine units: electric motor, heating element, drain pump, filling valves; for these purposes it remains unchanged.
To power the elements of the module, the mains voltage passes through the power supply and is converted. To power the microcontroller, you need a stabilized constant voltage of 5 volts, to power other elements 12 or 24 volts.
The first stage conversion is a rectifier circuit. It rectifies the mains alternating voltage into direct voltage without changing its value. Rectification takes place using a diode bridge on separate diodes or a ready-made prefabricated element.
Second phase - filtering or smoothing, the process of eliminating fluctuations and other influences. One or more high-capacity electrolytic capacitors act as a filter.
In the third stage the prepared voltage enters the conversion circuit. Here, the DC voltage is converted or inverted into a high frequency pulse signal. This signal is formed using a special multifunctional microcircuit - a PWM controller.
It is he who forms the signal with the desired parameters and feeds it to the pulse transformer.
A pulse transformer is similar to a mains transformer, but it has small dimensions and is made of ferrite. It lowers the voltage of the input signal to the desired value. After the transformer, the low voltage, as well as the high voltage at the input, is rectified and filtered.
Switching power supplies have one feature - they require feedback, that is, control of the output voltage. This is necessary for the correct formation of the pulse signal with changes in the load. For these purposes, the output voltage is supplied to the PWM controller, and, depending on the changes, forms the "correct" pulses.
In most modules, the power supply already generates two voltages of 5 volts and 12-24 volts, this is achieved by the presence of several secondary windings of a pulse transformer. But in some models, a voltage of 5 volts is generated from a higher voltage to power the processor. For this, step-down circuits or linear stabilizers of the LM7805 type and their analogs are used, and with their help the ready voltage is stabilized to prevent oscillations.
Switching power supplies in washing machine control modules have high efficiency and reduce the cost of the module, but at the same time they are frequent causes of failure for various reasons.