Usually people add the load to the collector, but I have a special case in which I have a relay connected to the collector, as is usually the case. But I also need to connect a BiLED to the emitter in order for the design to operate correctly. Is this bad form? The schematic is located @ http://tinyurl.com/o8ocp
2006-08-06
12:02:13
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8 answers
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asked by
↓ImWithStupid ░░▒▒▓▓
4
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Science & Mathematics
➔ Engineering
D8 allows for 1 coil to act as an OR sensor, it goes on when either transistor is saturated, making it only possible to put the BiLED (which only has one GND lead) at the emitter.
2006-08-06
13:06:30 ·
update #1
I could put the LED in parallel, if i used 2 LEDs and added one more Diode right before the collector and attach the LED lead directly to the collector
2006-08-06
13:08:16 ·
update #2
This is just a snippet and modified version from a whole schematic. In the full schematic a 10k resistor is placed at each of the transistors bases.
2006-08-06
13:18:42 ·
update #3
Your circuit is not complete.
There is nothing to limit the current into the bases so you need to add a resistor in series with each base. 10k will be ok.
The circuit should work but you should ensure that each relay coil's resistance is at least 300 ohms otherwise the collector-emitter current will exceed 20mA which is the normal maximum for a common red l.e.d.
Having a load in both collector and emitter is unusual so it doesn't at first sight fall into either of the normal categories of ce, cb or cc.
In passing I would mention a previous correspondent's error.
The emitter follower is the common collector configuraion.
Your circuit may be considered common collector (emitter follower) for the l.e.d. loads, and common emitter for the relay loads.
Addendum:
I have just read the previous post. Conecting the l.e.ds and their current limiting resistors in parallel with the relay coils is the way I would do it too. But you may have some undisclosed reason for doing it your way.
2006-08-06 13:13:35
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answer #1
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answered by dmb06851 7
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What you are attempting to do won't work because the LED probably will not pass enough current to allow the Relay to operate. You need at least 0.7V to turn on the LED. Therefore you need to calculate the current flow of the energized relay and add a resistor that will drop enough voltage to light the LED when this current passes through the emitter. The resistor and the LED in parallel with it are then placed in series with the emitter. The only fly in the ointment with this procedure is that the relay coil voltage will be reduced by the drop across the new series resistor.
2006-08-07 05:18:07
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answer #2
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answered by Buffertest 3
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Looking at your schematic I suggest a resistance in the base leads of the transistors to limit the base emitter current. Other wise those LEDS are toast.
Next suggestion is to make sure that the relay current does not exceed the LEDS ratings when that transistor saturates.
If it were me, I would place the LED with resistor in series, in parallel with the relay coil.
2006-08-06 12:53:49
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answer #3
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answered by Joel 1
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Well it seems that you aren't very familiar with transistors. The configuration you are talking about is called the emitter follower or common emitter. It is very common. It allows for very low output impedance(that is good). The configuration you are referring to that is connected at the collector is called a common collector which is used for high gain.
Everything should be fine.
2006-08-06 12:19:08
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answer #4
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answered by DoctaB01 2
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you'll blow any transistor in case you retain on with 60 volts between B and E right now. i imagine many your transistors were damaged already consisting of your attempt. you want to bypass decrease back to income properly how the transistor operating. To make it turn on, connect +60 volts to a 60K resistor, different area of 60K connects to the anode of a diode and the bottom of transistor ; cathod of diode connects to floor (B- similar on Emitter).
2016-11-23 13:21:13
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answer #5
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answered by Anonymous
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You've gotten some very good sugestions above, I would also add pulldowns to the bases before the base bias resistors
2006-08-06 15:07:14
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answer #6
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answered by Wattanabe 2
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As long as the load isn't 0 ohms, you'll have an emmiter follower design and everything will be fine....
2006-08-06 12:24:15
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answer #7
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answered by Anonymous
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I often end up posting the same thing on other sites
2016-08-14 03:14:31
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answer #8
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answered by Anonymous
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