Hi guys
Just need to clear a question up.
I take it transistors have to be logic level as well to work with arduino?
They have to be 5v right otherwise they dont open up all the way?
Is this what I must look at in the datasheet - VEBO / Emitter-Base Voltage
Thanks
M.....
No. You are talking about a Bipolar Junction Transistor, or BJT. It has no "levels". The Emitter to base characteristics are very similar in nearly all such transistors. You are thinking of a MOSFET, and the parameter is Vgs, or Gate to Source voltage.
ok because I have this transistor:
http://183.91.33.14/cache/www.fgxdz.com/technicData/TO-92L/C2383.pdf?ich_args=f828920f4b5a687c77e86df9e797229a_1_0_0_1_677652c319d2e8ee829572238ebeef05c29ff44ae84f0a477bb55fa986f68477_41c4940cf44d6722c9b43626dbd321da_1_0&ich_ip=33-6
Was just checking that it turns on and its fast enough to switch at 5us intervals?
And if im correct it can take up to 1amp current draw?
Thanks.
Hi,
Sorry link doesn't work, are you looking at a 2SC2383?
What is the application?
Tom.... 
2SC2383.pdf (83.2 KB)
Hi
Thats weird the link works if I click on it but yes the datasheet you have is correct.
I want to switch an IR led at its peak forward current which is 1000mA between 1us to 5us.
But I am only getting 77mA current draw with no resistor between power and the led and the led still seems pretty dull as if its not pulling enough current.
If I swap the connections of the collector and emitter the current draw goes way up but then the led does funny things(Pulsing)
But from what I read the negative side of the led connects to the collector and emitter goes to ground.
Im busy trying to find a scope to buy but they are flippen expensive.
So was just checking if the transistor will work.
Thanks
M.....
That link gives me a "405 Not allowed". Basically, though bipolar transistors are current controlled - the current into the base controls how much current flows between the collector and emitter (see the portion of the data sheet that shows the Hfe) so you need to provide a circuit that sources the required current (or sinks depending on the transistor type NPN vs PNP) sufficient base current to accomplish what you want. A MOSFET on the other hand is voltage controlled and the voltage on the gate controls what the current through the transistor does - the gate requires no current (except to deal with charging the capacitor that is part of the gate specs - that becomes very significant at high switching speeds). What you typically want to do with a switching type application (what you are doing with the IR LED) is drive the transistor into saturation - that is basically just providing enough current into the base to cause the transistor to turn on completely with the current you are trying to control. If you are trying to control 1 amp (1,000 ma) and the transistor has a Hfe of 100 for example, then the base current would need to be a minimum of 10 ma (and with an NPN transistor, the base-emitter voltage will be about 0,7v so you can calculate the base resistor from that. I would typically double that base current (but not exceed the drive capability of the Arduino pin).
A schematic of exactly what you have would really help!
How are you measuring, 77ma at 1us - 5us ?
What power supply are you using?
Thanks Gpsmikey good explanation I just have a 220 ohm resistor from the arduino pin to the base which at 5v would give a current of 22 mA is that correct?
How are you measuring, 77ma at 1us - 5us ?
What power supply are you using?
Im using a multimeter but I know the readings arent totally correct(Im looking into buying a scope,any suggestions for a poor guy lol) but the led is still very dim, I know it wont be as bright as a full on led but it should be close to it.
Ive seen some photos where people have run leds at there peak forward current, unlike theres my pulsed led is way dimmer than the fully on one
Im trying to power it from a 3.7v lipo which is at 4v charge now.
I also have a type of adjustable wallmart power supply 3v - 15v at 1amp
if I put my power supply on 15v the draw goes up slightly to about 90mA but still the led is dim.
If you are pulsing the transistor with 1-5us you cannot measure the on current with a DVM.
Hi,
1uS in 5uS is a duty of 10%, but I would think it takes a certain amount of time for the LED to get up to full brightness, 1uS may be to small.
You also need a series resistor with the LED, to limit the maximum current it will conduct.
10% duty will only give you a dim LED, try 1mS in 5mS, ie still 10% but more ON time to let the LED attain full brightness.
Thanks .. Tom...
PS Have you got the LED power supply gnd connected to the arduino gnd?
1/5 = 0.2 = 20%
That transistor needs morecurrent into the base than an Arduino pin can supply.
For example, page 2 under Electrical Characteristics,
The expected Collector-Emitter Saturation Voltage VCE(sat) with IB=50mA, to achieve IC=500mA is 1.5V.
And you want 1000mA.
I'd say you need a different transistor.
It has quite fast switching parameters, and requires very little current to drive the input capacitance of the gate.
Arduino pin thru a 200 ohm resistor would do fine.
Do you have a link to the datasheet of IR LED you are driving?
1uS in 5uS is a duty of 10%
What I meant by 1us - 5us was I actually put the led on for 1us and off for a 100us, the led been on for 1 us works better for my application but I can push it to 5us if 1us is a problem.
So I can pulse it 1us high 100us low or 5us high and 100us low both of them work.
You also need a series resistor with the LED, to limit the maximum current it will conduct
Yes thanks i got that I just didnt add it to see if i can get more current flowing.
Ive got an uno but im going to move it to a attiny later.
Im pulsing the led to stop sun interference.
The expected Collector-Emitter Saturation Voltage VCE(sat) with IB=50mA, to achieve IC=500mA is 1.5V.
And you want 1000mA.
These datasheets are driving me mad trying to understand all these CHARACTERISTICS .
So to turn this transistor on properly I would need 3v to get IC to 1000mA and IB=100mA?
Ok thanks if you could be so kind to tell me what are the important characteristics to look at when buying a mosfet or transistor for my application because I will have to get something locally here.
I do have a datasheet doesnt have any graphs or anything but this is all I got.
http://shop.rabtron.co.za/datasheets/WW-P05IR1W.pdf
Thanks
M......
Hi,
What I meant by 1us - 5us was I actually put the led on for 1us and off for a 100us, the led been on for 1 us works better for my application but I can push it to 5us if 1us is a problem.
1uS in 100uS is even less, thats 1% duty cycle, I'm surprised you can see it, or is it the receiver that is detecting it, can see it?
You need to check the LED spec to see if it will perform with 1uS pulse.
Im pulsing the led to stop sun interference.
What is the receiver, I assume you are trying to modulate the LED (transmitter) so that you can detect the modulated light above the normal sunlight.
Make sure that the receiver is not saturated with sunlight, if it is saturated it will never receive the LED light.
If its just for noise reasons, Tx at a duty of 50%, and bandpass the output of the detector at the modulation frequency.
Just a thought..Tom....
Undermentioned:
Im using a multimeter but I know the readings arent totally correct(Im looking into buying a scope,any suggestions for a poor guy lol)
This is the scope I have - works quite well for all of my needs although it does have a somewhat goofy menu (it is not intuitively obvious how to save a screenshot to a USB flash drive, but it does work quite well). This is one of the ones that "Dave" on eeblog tested some time ago. I don't know what the range of prices is on it right now, but that is where I bought mine several years ago. Definitely a worthwhile investment if you are working with any of these microprocessor based things and logic chips!
1uS in 100uS is even less, thats 1% duty cycle, I'm surprised you can see it, or is it the receiver that is detecting it, can see it?
The receiver module is a camera module, well I cant see it because its IR but the camera does.
You need to check the LED spec to see if it will perform with 1uS pulse.
What Ive seen on the internet leds can pulse very very fast dont know about mine though.
Peak Forward Current 1000mA (1/10 Duty Cycle, 0.1ms Pulse Width) dont know what that means but there it is.
But I am pulsing it less than that, so in theory I could put more current through?
Im using a multimeter but I know the readings arent totally correct(Im looking into buying a scope,any suggestions for a poor guy lol)
How are these computer scopes, like this one is in my price range.
http://www.saelig.com/spcl-pc-scopes/vds1022.htm