Open Collector Driver
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-02
The illustrated open collector driver circuit is capable of sinking a predetermined current magnitude in the DOWN level. When input A is UP, transistor T2 conducts, causing T4 to conduct and T5 to be off. When T5 is off, current flow into the resistors RH is inhibited such that T5A, T6 and T7 are respectively off and output A is UP. Resistors RH are included to prevent current hogging in any one of the output devices. It is to be noted that each output device T5A, T6, T7 discharges through RH, R1, into T4 (active pull-down). When input A is pulled DOWN, T1 will turn off T2 and T4 such that T5 conducts, sending base current into T5A, T6 and T7. Output A will fall. Transistor T3 is used to inhibit the driver circuit. When Z is UP, T3 conducts, causing T5 to be off, causing the output A to UP.