Low-Cost, High-Accuracy, Non-Adjustable Printer Coil Pulse-Width Compensation Circuit
Original Publication Date: 1988-Apr-01
Included in the Prior Art Database: 2005-Feb-15
The print head used in the IBM 4207 and 4208 requires that the width of the energizing pulse applied to the coil be narrower for high voltages and wider for low voltages. Fig. 1 illustrates the functional relationship. The compensation circuit is shown in Fig. 2. The 6 ms trigger pulse is generated by the printer controller. This causes the LM339 to discharge CT . R5 is a low value resistor and limits power to the LM339 output. At the end of the trigger pulse, the capacitor CT charges towards V, which is nominally 35 volts, through RT . The rate of charging is primarily determined by the values of RT, CT and V. Thus, if V is somewhat high, the charging rate will be higher; if V is a bit low, the charging rate will be lower.