Electronics

jdl · Joined: 10 Dec 2006 Posts: 5

I had a question about transistors. As far as my level of knowledge on this subject, I'm several steps below a novice, if that's possible.

I was looking at a diagram on an automotive circuit, it showed a transistor in the distributor assembly. The transistor was on the negative leg of the coil primary circuit, the collector leg was going toward the coil, the emitter leg went to the vehicle computer. The base leg went to chassis ground. That didn't make sense to me.

The way I understand it ,the collector leg is + and the emitter leg is -, a small voltage is applied to the base leg in order to close the switch and have continuity between the collector and emitter. The main current flows from the collector to the emitter. With a bipolar transistor, I guess there is a pnp and a npn, the direction of current flow depends on which one you use. In the coil example given, shouldn't the base leg carry a small voltage to control the main circuit, and the emitter leg go to chassis ground? Wouldn't that be safer for the vehicle computer than to have the emitter leg going to the computer? thanks

neon · Joined: 25 Feb 2006 Posts: 580

You are wrong to assume that current goes from collector to emiter and it flows one way. If the transistor is saturated then current can and will flow both directions. You have two diodes in parallel. IF you bother to look at the chrarcteristics you cab see that.actualy if a want a low level clamp i would use a pos. on the base of a PNP and a positive on the collector usualy a 2n2907 I like those guys.And finaly transistors have many modes of operation gnd base gnd collector and gnd emiter . every model is good for some aplication in design as required

jdl · Joined: 10 Dec 2006 Posts: 5

The information I have says, with a bipolar transistor, the main current flow goes from the collector to the emitter or from the emitter to the collector, depending on which transistor you used, pnp or npn.

In the example I gave, where the transistor was on the coil negative primary circuit, following conventional flow, the emitter leg is down and the arrow is pointing down. The main current follows the arrow, also the smaller base current would follow the arrow, with main current going from the collector to the emitter. The base can't be grounded in that example?thanks

neon · Joined: 25 Feb 2006 Posts: 580

arrow pointing away from base i asume that means an NPN transistor. and it is not that the emiter follows the base but the other way around. THAT TRANSISTOR WITH THE BASE TO GROUND WILL TURN ON as soon as there is base current How you do that is supply a difference voltage from base to emiter of the right polarity. since you have no idea what the computer has inside you will never know how it works.ha! ifit works then there must be a potential difference from base to emiter. and next time attach a schematic so we can all see the mistery.

jdl · Joined: 10 Dec 2006 Posts: 5

go to the link for the 95-98 2.5 stratus, the transistor symbol is in the distributor assembly. With conventional flow, the main current goes from the collector to the emitter. The smaller control current has to follow the arrow, also, that is according to an electronics tutorial, that smaller current would go from the base to the emitter leg.

I'm sure there is no mystery to a person trained in this field, but,to an untrained person like myself, it is starting to look like Greek.

I just wondered what was going on, with each leg of the transistor. I thought the collector and base leg were fairly straight forward. Your correct, I don't what is going on with the emitter leg. I'm not even sure what type transistor that is.

I had to edit out the link, I posted, I tried it,yesterday, after I posted it and it worked. Not working today.

You can go to the autozone site, click on(vehicle repair guides) for the year--make and model listed above, follow the links, there are wiring diagrams. I tried to highlite the diagram itself, wouldn't work.

neon · Joined: 25 Feb 2006 Posts: 580

Well you got to get the info right.and for the life of me i don't know who makes the STRATUS. so i give up. i know who makes LOTUS and LEXUS i own 3 of them but stratus ?did it ever down on you that that is not a transistor but a photo coupler of a sort.

jdl · Joined: 10 Dec 2006 Posts: 5

Sorry about that, it is a dodge stratus. Oh, well, thanks for your time, I give up, also.

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