Print Hammer Drive Circuit
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
A chopper-type print hammer drive circuit is simplified by using low impedance voltage sources to determine hysteresis current levels for the drive coil. A variable reference voltage circuit for a plurality of hammer drivers provides non-linear compensation for variations in the driver supply voltage to stabilize hammer flight time. The chopper drive circuit is shown in Fig. 1 where hammer drive current from supply voltage 1 through transistor 2, hammer coil 3 and current sense resistor 4 to ground is controlled by comparator 5 and transistor 6. The hysteresis levels of current through coil 3 are established with ground referenced low impedance voltage sources by (Image Omitted) using the Vbe of transistor 6 and Vce of comparator 5.