Need help from an electronics wizz

[Jay Payne]

Wonder if anyone can help me.

I have a 2volt supply that i want to use to switch a 12-14 volt output.

Ive been looking for a 2 volt relay but cant find any.

My Bro has found some info on using a transistor to do this but the switch voltage needs to be dropped to around 0.7v for the transistor. Is this right?


Any advise or diagrams would be very helpfull.

Thanks

 

[sn00p]

http://www.kpsec.freeuk.com/trancirc.htm

See the section:

Choosing a suitable NPN transistor

Basically, depending on what transistor you choose you can use that to determine the base resistor to turn on the larger current to drive the relay coil.

You'll also need to know the coil resistance of the relay and make sure that the transistor can handle that much current flowing through it.

Edit:

And if you're driving an inductive load then you'll need a protection diode as shown to stop back EMF, which would be bad.

 

[Jay Payne]

sn00p, Thanks so much for your post but its a little over my head. Im a car technician so autoelectrics are no problem but I dont really understand much about transistors etc.

Basicly I have a 2 volt source, that comes on and off. I want to wire some (Bright-ish) led's to this source but run them off the cars voltage (12v-14.5v)

Is a transistor my only option?

OR could I run some led's off the 2 volt source in anyway? eliminating the need for the 12v supply?

 

[sn00p]

sn00p, Thanks so much for your post but its a little over my head. Im a car technician so autoelectrics are no problem but I dont really understand much about transistors etc.

Basicly I have a 2 volt source, that comes on and off. I want to wire some (Bright-ish) led's to this source but run them off the cars voltage (12v-14.5v)

Is a transistor my only option?

OR could I run some led's off the 2 volt source in anyway? eliminating the need for the 12v supply?

Ok, you don't need a relay, but you do need to know what LED's you will be using and how many there are, you need to know the led forward voltage & current and how many are going to used, this determines the resistor that needs to be used which determines the load for the transistor.

 

[Jay Payne]

3 led's. Can buy them to suit. Any suggestions?

Slowly reading through that site and some of it is making sense.

Have i got this right so far?

C will be my 12volt
E will go to the led's
B will be my 2volt switching source

 

[richy22]

Post up some more information on what types of led's your using and im sure you'l get all the info on what you need!

 

[Hutchie]

you need a monkey

send 2v to his tail
it will shock him and he will turn your led's on

 

[sn00p]

3 led's. Can buy them to suit. Any suggestions?

Slowly reading through that site and some of it is making sense.

Have i got this right so far?

C will be my 12volt
E will go to the led's
B will be my 2volt switching source

You need to buy the right leds for what you're doing! If you want bright ones, buy bright ones.

The forward voltage & current will differ depending on colour & brightness! Don't select ones with integrated resistors though!

Collector has 12V supply driving the load (your leds).
Base is the drive (2V signal)
Emitter is to ground.

 

[richy22]

An example of what you could use....???

http://uk.farnell.com/avago-technologies/hlmp-cw30-ps000/led-5mm-30deg-wht/dp/1003364

 

[Jay Payne]

Right starting to get it. So if I went to say, Maplins and selected some LED's they could supply a transistor to suit? or would I need to know what I wanted? (Not sure how clued up they are in there)

Emitter is to vehicle ground or 2volt supply ground? (This could be a common ground, not sure atm) Does the emitter need to be ground for the benifit of C or B or both?

 

[Jay Payne]

An example of what you could use....???

http://uk.farnell.com/avago-technologies/hlmp-cw30-ps000/led-5mm-30deg-wht/dp/1003364

Says ''Voltage, Vf Max:4V'' I'm guessing no good for running off the cars voltages?

 

[Jay Payne]

Not sure if this matters but the circuit will not be switched on for very long periods. Maybe a few seconds at most with a few seconds break

 

[richy22]

Says ''Voltage, Vf Max:4V'' I'm guessing no good for running off the cars voltages?

But if your running 3 of those leds off the same 12v power supply

 

[Dink]

Rapid is your friend

i'd say anything above 1A rated current will be more than enough for a couple of LED's (most LED's would melt once you put more than 100mA through them)

 

[Jay Payne]

Thanks Dink, looks like they should have what I need. Although I still have no clue.

Went into Maplins earlier and the guy was no help what so ever, he just said I had to give him some part numbers for what I needed and he would get them out of the drawers in the stock room.

I get the circuit layout now but still unsure what transistor I will need/how do I figure it out after choosing my LED's. Still need help guys please.

 

[Dink]

This page should show you what you need