Saturation Control Circuit for Use in a Five-Volt Common Bus Environment
Original Publication Date: 1988-Jul-01
Included in the Prior Art Database: 2005-Feb-15
A modification of circuits described in [*] is made which permits use in a bipolar-field effect transistor (BIFET) tri-state off-chip driver (OCD). Referring to the figure, bipolar feedback transistor T6 turns on and takes excess base current driven into bipolar transistor T8 when output OUT falls to about 200 mv. As a result, transistor T8 will not saturate. The output voltage at which transistor T8 turns on is dependent upon the ratio of resistance values of resistors R2/R1. When the OCD is tri-stated, the n-channel field-effect transistor (n-FET) T4 pulls the base of transistor T6 to ground. If the output OUT is driven high (approximately 3-5 volts), the output voltage OUT will divide between the base-emitter junctions of bipolar devices T10 and T6. Biasing the base of transistor T10 to 2.