If desired a fourth diode can be coupled between the current sink collector and the input of a source follower driver to soften the saturation characteristic of the current sink transistor.įIGS. Since the three diodes cannot conduct simultaneously, the Darlington pair cannot conduct while the current sink transistor is conducting and current spikes are avoided. Since all three diodes are driven in common from the collector of the sink transistor, they can act as switching elements to control the current sourcing action of the Darlington pair. A third diode is coupled from the base of the Darlington driver transistor to the current sink transistor collector. A second diode is coupled from the base of the Darlington output transistor to the current sink transistor collector.
The current sink transistor has a diode coupled in series with its collector poled to conduct the sink current. A current sink transistor connected to the output terminal provides the sink capability. The output stage employs a Darlington connected transistor pair with a current source input to act as a current source to an output terminal.
These and other objects are achieved as follows. It is a further object of the invention to provide a totem pole circuit in which the current sourcing action is terminated by the current sinking action whereby the two actions do not occur simultaneously. It is an object of the invention to provide a totem pole output stage in which current spikes are minimized. When excessive, the resulting heating can be deleterious to the integrated circuit (IC) that employs the stage. Since such a spike produces no useful output, it is parasitic and only results in wasted power. The spike will become appreciable at the high operating frequencies. Such stages typically will briefly source and sink current simultaneously so that a current spike, or pulse, will occur. Totem pole transistor output stages are used to drive loads wherein the stage can either source or sink output current.
The circuit of claim 2 further including a fourth diode coupled between said collector of said second output transistor and said base of said emitter follower transistor and poled to be conductive when said second output transistor is conductive. The circuit of claim 1 wherein said base of said second output transistor is driven from an emitter follower transistor having its base coupled to said signal input terminal.ģ.
A totem pole transistor output stage circuit capable of sourcing and sinking output current in a load, said circuit having signal input and output terminals and comprising:įirst and second power supply terminals connectable to a source of operating power Ī first output transistor having its emitter coupled to said output terminal, its collector coupled to said first power supply terminal, and a base Ī first driver transistor coupled in Darlington configuration to drive said first output transistor and having a base Ī second output transistor having its collector coupled to said output terminal, its emitter coupled to said second power supply terminal, and a base coupled to said input terminal Ī first diode coupled in series between said collector of said second output transistor and said output terminal and poled in a same direction as the base-emitter junction of the second output transistor Ī second diode coupled between said collector of said second output transistor and said base of said first output transistor and poled in a same direction as the base-emitter junction of the second output transistor Ī third diode coupled between said collector of said second output transistor and said base of said first driver transistor and poled in a same direction as the base-emitter junction of the second output transistor andĪ constant current device coupled between said first power supply terminal and said base of said first driver transistor.Ģ. These are additional considerations to include in a fuller analysis not done here.1. We don't know if this is important, or not, just yet. One of the first things to understand is the capability of the output, as that is what will be driving other inputs. Simulate this circuit – Schematic created using CircuitLab Let me draw out the schematic using the editor (you should have done this, too.)