Transformerless power supply: purpose, features, operating principle of the device
Power supplies for personal computersare built on transformerless network connection circuits (in fact, this is a pulsed power supply). They are characterized by high efficiency, small overall dimensions and low weight. However, the transformerless power supply unit has a significant drawback - impulse noise, which has a negative impact on other PC circuits and other consumer electronic devices. Therefore, each such product undergoes a serious check for electromagnetic compatibility with other equipment. In addition, the transformerless power supply unit does not have a galvanic isolation in the part of the electrical circuit from the mains supply voltage. This, in turn, requires the use of special security measures during the repair of such a product.
Transformerless power supply: main functional parts
The device consists of the following components:
- network rectifier;
- interference suppression filter;
- start-up circuit;
- Capacitive filter;
- voltage converter based on a pulsed power inverter;
- circuit of output voltage formation;
- control scheme;
- circuit of formation and transmission of feedback signals to the control circuit.
Depending on the model and the functionaldestination, the transformerless power supply unit can contain additional circuits, such as a linear regulator in discrete or integral design, protection against overloads of input and output voltage and current, as well as interference suppression circuits. In addition, such power supplies can include circuits for generating special control signals, which ensure the coordination of the operation of the device with the power supply circuit.
Principle of operation
Pulse universal power supplies forobtaining a DC voltage, a triple conversion of the input voltage is performed. First it straightens and smoothes out. The result is a DC voltage, after which the formation of rectangular pulses with a frequency of tens of kilohertz occurs. After that, the received pulses are transformed to the secondary side with the corresponding coefficient, and straightening and smoothing occurs again. The main node of transformer-free power supplies are the key voltage converters, and in the first place their power part (high power output cascade). These cascades are usually divided into single-cycle and two-stroke.
Adjustable power supplies
To adjust the output voltage intransformerless devices most often use the technique of pulse-width modulation, which consists in changing the duration of pulses, as well as pauses between them. The conversion frequency remains unchanged. The relationship between such quantities as the duration of a pause and the pulse depends on the value of the output voltage. It automatically changes to maintain the output voltage within the nominal value.