Timeline for Can a transistor's emitter and collector be used interchangeably?
Current License: CC BY-SA 3.0
9 events
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| May 19, 2015 at 14:57 | comment | added | Ignacio Vazquez-Abrams | @sherrellbc: I think I finally got your question. And it only took two months :P The conduction path for Q4 when Q3 is off is from the outside circuit, i.e. the next logic stage. | |
| Mar 17, 2015 at 19:17 | comment | added | Ignacio Vazquez-Abrams | Q3 can only be off if Q2 is on and hence sinking the current from R2. This turns Q4 on. | |
| Mar 17, 2015 at 19:11 | comment | added | sherrellbc | Just to ask it here and not convolute the other thread more than it already is, If Q3 is off, how can Q4 be active and conduct without a path to do so? | |
| Oct 23, 2014 at 11:47 | comment | added | user16307 | im still confused 1)why do you say " Q2 base is 1.2V, Q1 base is about 1.8V"? how do we know that? 2)i thought in TTL logic outputs and inputs are between 0 to 5V. in this case you tell that 5V is the Vcc. so what will be the output ON voltage (at Q4 collector)? | |
| Oct 23, 2014 at 10:51 | comment | added | Alan Campbell | @user16307 Q2 base is 1.2V, so Q1 base is about 1.8V. Vcc=5V (TTL) I = 3.2/4K = about 0.9mA always flowing thru R1. 2) If you short R3, there is no current limit for Q2. It saturates, collector approaches 0.2V, Q3 and Q4 are driven to cutoff. 3) If Q1 base is 1.8V then A or B need to be below 1.2V to come "on" and draw current from R1. | |
| Oct 23, 2014 at 10:13 | comment | added | user16307 | @Alan Campbell thanks i have 3 confusions here.. 1)why do you call it current source? 2)if R3 wouldnt exit Q2's emitter would be grounded, what woıld happen in that case? would current divides and equally flow through collector and emitter of Q1? 3) what should be the proper amount of voltage applied to A and B to reverse bias the emitter base junction? | |
| Oct 23, 2014 at 2:32 | comment | added | Alan Campbell | R1 and Q1 are acting as a current source. If A or B (or both) are low, they take enough current away (current "sink") to stop Q2 conducting. However, when both are high, the current has no path left other than the forward biased base-collector, causing Q2 to conduct. | |
| Oct 23, 2014 at 1:43 | vote | accept | user16307 | ||
| Oct 23, 2014 at 1:40 | history | answered | Ignacio Vazquez-Abrams | CC BY-SA 3.0 |