Print Head Driver Protection Circuit
Original Publication Date: 1985-Nov-01
Included in the Prior Art Database: 2005-Feb-19
This circuit protects print head wire driver circuitry from being destroyed or damaged when abnormal input drive conditions are applied. Over-current or old over-voltage conditions or drive pulses applied for too long a time may subject the print head driver circuitry to excessive heat and cause damage. The print head in an average wire matrix printer is an expensive portion, and failures in its drive circuits are both vexatious and costly to correct. The figure shows a simple sensing circuit that is responsive to the pulse widths of the input drive signal. When the signal pulse width is longer than the specified value, the sense circuit shuts down the driver and saves both the driver and the print head from damage or destruction. FET drivers are used due to the simplicity of their bias circuitry, i.e.