Hello Everybody
Trying to work out why am i having such low voltage on the emitter on the 2N4401
24V on collector, 4.7V on emmiter. Arduino 5V
Vin 24V
I`m require to see ~24V on emmiter.
I`ll appreciate any help
Hello Everybody
Trying to work out why am i having such low voltage on the emitter on the 2N4401
24V on collector, 4.7V on emmiter. Arduino 5V
Vin 24V
I`m require to see ~24V on emmiter.
I`ll appreciate any help
Hi,
You have made an "Emitter follower" and that's what it is doing, following the base voltage.
You need to look at transistors and amplifiers in some book.. You will need to add a transistor to have the base voltage of the 2N4401 (A small NPN transistor) approach 24V. You will still have a drop of about 0.7V
Hi.
Can i do anything with the current design? I`ve got the board made already hence the issue.
http://www.rason.org/Projects/transwit/transwit.htm -> figure 2 will sort that out?
You can't use an NPN transistor as a high side switch if Vin > 4.3 V. The schematic shown in figure 2 on (http://www.rason.org/Projects/transwit/transwit.htm) won't work in your case because you can't turn the PNP transistor off completely with a 5 V Arduino.
You need something like the diagram below.
mOskit:
I`ve got the board made already hence the issue.
Time to get your scalpel out and fixe it with mod wire.
Did you miss the bit on that page that said
However, in the NPN transistor, R1 must be shorted to the positive end of the supply to turn the switch on.
Got it. so basically i can set output pin to LOW and use PNP 2N3906 instead of NPN 2N4401 to switch High side right?
mOskit:
Got it. so basically i can set output pin to LOW and use PNP 2N3906 instead of NPN 2N4401 to switch High side right?
That will turn on the transistor but in order to turn it off you have to supply at least 11.4V to the emitter’s base resistor.
Grumpy_Mike:
That will turn on the transistor but in order to turn it off you have to supply at least 11.4V to the emitter’s resistor.
So thats fine as the emmiter will have 24V constantly on and the " load is on the collector side. right?
Sorry I meant to say the base’s resistor.
Origional post now corrected.
That circuit will also fry your Arduino pin as it will apply 12V to the output pin when you try and turn the transistor off.
So this is the only way right? (see attached)
Not sure about the resistor values. I think 2K for R19, R20 and 100k for R25, R26 followed by 2K2 for R23 and R24?
They are not too critical if the current is not high, what is the current you want to switch.
It`s just a signal to another micro controller (or relay) on the machine. I guess few mA but still waiting to get this confirmed.
I guess few mA but still waiting to get this confirmed.
It would be a good idea to actually know details like this, and design and test appropriate circuitry, before you have a custom board made.
If its a few mA an opto-isolator might be simpler.
Hi,
Sounds like you are switching to some industrial devices/PLC.
Opto would have been easier and provide isolation from the other system.
Pity you did not prototype first.
Tom...
I actually did a prototype. It was just about making another 2 sided board which frustrating me a lot when I try to lineup transfer paper. Simply I had 2 pnp proxy switches, and now I have 8, so I trying to interface those 8 into 2 original inputs on the machinery with individual behaviour.
Why the obsession with a PCB? Why not make stuff on strip board?
Trying to be pro for my bosses
Grumpy_Mike:
Why the obsession with a PCB? Why not make stuff on strip board?
mOskit:
Trying to be pro for my bosses
A properly made strip board can be even more impressive.
Especially compared to a custom PCB, having had a little surgery to make repairs, and perhaps even with a little bit of smoke arising from various places.
A PCB that doesn't work properly is, unfortunately, not impressive.