Driving method of heat element array

Abstract

An array of heat elements is driven by a driving circuit including a plurality of control units operative to sequentially carry out generation of heat efficiently even with using a relatively small capacity of a power supply and without relying on processing by CPU, thereby achieving fast heat generating operation while saving electric power. The thermal head is provided with a plurality of heat generating units each being comprised of a heat resistive element for generating heat by current flow and an electrode for supplying a current to the heat resistive element, and a plurality of switching elements for controlling supply of current to respective one of the heat generating units. The heat generating unit is constructed such that its resistance increases according to a temperature rising of the heat resistive element by the current supply so as to reduce an output of a driving current. The switching element is composed of, for example, a thyristor operative to turn off the current supply when the current flowing therethrough is reduced below a given level. A voltage between the switching element and the corresponding heat generating unit is monitored to detect the turning-off of the switching element so as to constitute a turning-off detector. The detection of the turning-off indicates the completion of the heat generation or the finish of current supply. Thus, after the detection of the turning-off, a next switching element is initiated to start generation of heat in an adjacent or subsequent heat generating unit.