TTL_COMPATIBLE_SCHMITT_TRIGGER

Published:2009/7/7 4:15:00 Author:May | From:SeekIC

The comparator has an output pull-up resistor RL. and is connected up to operate as a Schmitt trigger using the single rail supply Vcc. The feedback resistors R1 and R2 give upper and lower threshold levels VT+ , VVVTW, respectively. VT+ , is easily set by suitable resistor selection but there is little independent choice of VT- because VT- cannot exceed VCE(SAT) In Fig. 15-13B current-source, comprising the transistors RE, Rg produces a current I～:(VEB/RE), VEB (～0.65 V) being the emitter-base voltage of Q1 and Q2. Fig. 15-13C shows the results of a practical test using the circuit of Fig.15-13B, and the following operating and component data: Vcc=5 V; RL = 1 K ohm; R1=R2=10 K ohm; RB=3.6 K ohm; RE=1K ohm + 10 K ohm pot; Q1=ZTX500; Q2 - ZTX500.



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