The high input case (logic 1) is trivial - the left 'diode' is off and the current is diverted (steered) entirely through the right 'diode' string. As a result, the base current of the input transistor is diverted ('steered') through the lower output part of the previous stage to ground and the circled transistor is off. The right diode is the string of three 'diodes' in series: the base-collector junction of the input transistor, the base-emitter junction of the circled transistor and the base-emitter junction of Q2. In TTL the output stage has two transistor amplifiers (one CE and another CC) connected in a push-pull configuration to act as current sink and source at the output stage. The left diode is the base-emitter junction of the input transistor. In the TTL family, the Totem-pole circuit on the output is used to provide active pull-up and active pull-down. Thus, at low input voltage (logical 0), there are two 'diodes' in parallel. The base-emitter junctions of the circled transistor and the output transistor Q2 can be also considered as 'diodes'. The input transistor can be presented as two 'diodes' ( base-emitter and base-collector junctions) with common anodes (the base). VDE-approved: EN6, EN60065 or EN60950-1 (Note 1)ĬQC-approved: GB4943.The input part of the TTL logic gate above can be easily explained at low input voltage (logic 0) by the phenomenon of current steering, the essence of which is: If we connect two diodes with different forward voltages in parallel, the current will flow through the diode with lower forward voltage. figure shows the circuit of a TTL NAND gate with open collector output. this problem of TTL with totem-pole output is overcome in TTL with open collector output. (8) Common-mode transient immunity: ☒0 kV/µs (min)ĬUL-approved: CSA Component Acceptance Service No.5A File No.E67349 TTL with totem-pole output has a major problem that the two outputs of the two gates cannot be connected together. (7) Propagation delay time: tpHL = 190 ns (max), tpLH = 170 ns (max) (6) Threshold input current: 7.5 mA (max) (1) Buffer logic type (totem pole output) It is suitable for directly driving a small IGBT or power MOSFET. The TLP152 has a totem-pole output that can both sink and source current. The photodetector IC chip has an internal shield to provide a high common-mode transient immunity of ☒0 kV/µs and thus superior noise immunity between the input and output pins. The TLP152 is a photocoupler in an SO6 package that consists of a GaAlAs infrared light emitting diode (LED) optically coupled to an integrated high-gain, high-speed photodetector IC chip.

Totem pole output