negative printhead supply

[:10] negative printhead supply Thermal and metal foil printers are equipped with a printhead which usually requires a rather high voltage, in order to be driven. For example, a metal foil printer needs a voltage of approximately 30 V. Some thermal printers require as high as 50 V! The maximum current that is required by the circuit is essential with printhead power supplies but good stabilisation is lens important. The printhead of metal foil printers must "heat" the surface of the foil paper, so that the metal parts of the foil evaporate, thus obtaining the "print" that is wanted. The current value required for this process is about 1 A. Basically the circuit is really an ordinary stabilised power supply. Resistor R 1 ensures that the circuit can "start". The output voltage level can then be set with preset P2, via a feedback circuit, consisting of Dl, P2, R7 and T2. The range mainly depends on the value of zener diode Dl and the level of the input voltage. In our case the outpu...