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Topic: What resistor value at the transistor base? (Read 7428 times) previous topic - next topic

raschemmel

Quote
My meaning of Vemitter means 'voltage at the emitter', obviously.
You still haven't realized there is no such parameter ? Can you find that on a datasheet ?(no)
As with everything else you post on this forum, you just made that up because you have no formal training in electronics.

Southpark

#46
Jul 10, 2016, 11:13 am Last Edit: Jul 10, 2016, 11:15 am by Southpark
You still haven't realized there is no such parameter ? Can you find that on a datasheet ?(no)
As with everything else you post on this forum, you just made that up because you have no formal training in electronics.
You're the one that assumed that 'Vemitter' comes from a data sheet. You just conjured this 'data sheet' thing in your own mind. Was already mentioned to you (by me) that I meant that 'Vemitter' just means voltage at the emitter. So just accept it, and move along.

raschemmel


Quote
I meant that 'Vemitter' just means voltage at the emitter. So just accept it, and move along.
The problem is that the voltage on the emitter is 0V because it is connected to ground so what is the point of saying Vemitter when you can just say GND ?

Southpark

#48
Jul 10, 2016, 11:19 am Last Edit: Jul 10, 2016, 11:24 am by Southpark
The problem is that the voltage on the emitter is 0V because it is connected to ground so what is the point of saying Vemitter when you can just say GND ?
To ensure that Ve (or Vemitter) is taken into account if somebody connects the load on the emitter side (emitter follower configuration). Watch it with your deliberate snubs raschemmel.

raschemmel

#49
Jul 10, 2016, 11:24 am Last Edit: Jul 10, 2016, 11:29 am by raschemmel
Quote
To ensure that Ve (or Vemitter) into account if somebody connects the load on the emitter side (emitter follower configuration).
Can you not see where the load goes in the OP's schematic ?

Do you see anyone connecting a load between the emitter and ground ?
Is anyone else concerned about that possibility in this thread ?
What configuration do YOU call this ?


BTW,
Can anyone explain why the ground zigzags from the emitter to the ground symbol ?

What's that all about ?

Southpark

#50
Jul 10, 2016, 11:31 am Last Edit: Jul 10, 2016, 11:37 am by Southpark
Can you not see where the load goes in the OP's schematic ?
Let me enlighten you. The OP did not post a schematic at first. The OP posted a schematic at some stage after their first post. So it makes sense to use Vemitter.... to cover bases.

Quote
What configuration do YOU call this ?
It's a common emitter configuration. But you called it an open collector configuration. I don't mind what you call it. You can call it whatever you like.

raschemmel

#51
Jul 10, 2016, 11:36 am Last Edit: Jul 10, 2016, 07:23 pm by raschemmel
Quote
Let me enlighten you. The OP did not post a schematic at first. The OP posted a schematic at some stage after their first post. So it makes sense to use Vemitter.... to cover bases.  
With no formal electronics training I doubt you will be enlightening anyone.

Try doing a "sanity" check on your posts before posting. See if you can find  anyone else who is saying something similar because you are clearly just pulling stuff out of the air ( making it up as you go along).

 We like to represent professional electronics opinion on this forum not amatuer conjecture.

If you are not an electronics person by trade then maybe you should research your information a little better, maybe with Google. ( like don't make up parameters that don't even exist).

Your contributions are appreciated if they are based on fact and not conjecture.

There are no "bases" to cover . This application has always been a low side switch is not going to be changing.

Southpark

#52
Jul 10, 2016, 11:53 am Last Edit: Jul 10, 2016, 11:53 am by Southpark
I'm amazed that this thread has gone for so long. As has been mentioned a number of times now, the correct way to drive the transistor into saturation for switching is to provide Ic/10 or at the very least, Ic/20 to the base.
Agreed. A great rule of thumb you mentioned OldSteve. The Ic/Ib = 10 one

OldSteve

Agreed. A great rule of thumb you mentioned OldSteve. The Ic/Ib = 10 one
At least I got that right. :D

(Actually, I think it was the OP's schematic that had me thinking there were only 10 LEDs / 200mA collector current. I should have read back from the first post. :( )
Please do not PM me for help. I am not a personal consultant.
And others will benefit as well if you post your question publicly on the forums.

Southpark

#54
Jul 10, 2016, 12:01 pm Last Edit: Jul 10, 2016, 12:03 pm by Southpark
At least I got that right. :D

Haha! You were spot on. You had it right mate. Thanks for showing that.

raschemmel

In the OP he approximates, saying " maybe 15 - 20 LEDs per transistor"

OldSteve

In the OP he approximates, saying " maybe 15 - 20 LEDs per transistor"
Yeah, as I've since seen when I revisited it. I read that post a couple of days ago, then today I picked up at a later point. Saw the schematic and another reference to 10 LEDs and went with it. As I said, my bad.

Not to worry, all's well that ends well. :)

It's been a moot argument anyway really, since the current would be far lower if the LEDs are set up in series strings. Strings of 2-3 LEDs in series would work well and lower the collector current to about 1/3 to 1/2 the present value.
(Then the resistor calculations/discussions would have to start all over. That might be fun. :D )
Please do not PM me for help. I am not a personal consultant.
And others will benefit as well if you post your question publicly on the forums.

Southpark

#57
Jul 10, 2016, 12:15 pm Last Edit: Jul 10, 2016, 12:17 pm by Southpark
In the OP he approximates, saying " maybe 15 - 20 LEDs per transistor"
But soon after.... we said...consider 1 arduino digital output per transistor.

raschemmel


Southpark

#59
Jul 10, 2016, 12:25 pm Last Edit: Jul 10, 2016, 12:35 pm by Southpark
Then why use transistors ?
To switch one set of 10 LEDs. Otherwise.... just use 1 digital output and a suitable switch circuit (MOSFET) that handles more current to cater for the number of LEDs that the OP needs to turn on. Whatever you like.

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