The basic structure of a typical dot matrix printer switching power supply

The basic structure of a typical dot matrix printer switching power supply

Shown is the basic structure of a typical dot matrix printer switching power supply. As can be seen from the figure, M51978 is a switching oscillation integrated circuit, VT1 is a switching field effect transistor, AC 220 V is filtered and the bridge rectifier stack outputs a +300 V DC voltage, and this voltage is added to the power supply end of the switching oscillation integrated circuit
through the starting resistor
Ri vcc, at the same time, is added to the drain of the switching field effect transistor VT1 through the primary winding of the switching transformer . The switching transformer L2 is a positive feedback winding, which provides a positive feedback signal for the switching IC to start the switching power supply . Then the secondary rectification and filtering outputs a DC voltage. .