Have 1 vdc - I need to turn on separate 12vdc circuit with this 1 vdc

Please help me come up a SIMPLE solution to this problem.

I already have a simple circuit that is activated by sound, which beeps and blinks a small led.

I would like to use the 1 vdc that is lighting the led to switch on (and off) a 12 vdc circuit that will be used to light a more powerful LED

I keep hearing NPN, but I sure could a simple schematic which would give the transistor that I could use, along with the values of the other components.

thanks,
grampa rich
(not rich grampa as the kids think)

Hi Grandpa

A little more information would go a long way. If you are lighting a LED you may be able to use an opto coupler to get where you want to go. However, how much current will you be switching at 12 volts? You may need to use an opto coupler to turn on a NPN transistor 9or other transistor) to in turn drive your 12 volt load.

Welcome to the ETC forums!

Ron

Hi there Ron,
It's kinda funny that you would mention using the led to trigger an opto coupler. (I'm not really sure what that is, except it sounds like photo/electric stuff)

So it would mean that : (a) I am using this little 10 second record/ playback module to provide the sound to (b) trigger the sound activated module

which blinks the led which will (c) activate the opto controler which will (d) switch on the 12vdc to light (2) 1 watt led's.

I LOVE IT !!!

I just answered your question about how much current will be switched in the 12 vdc circuit.

Is this opto coupler circuit complicated ? expensive ?

It sounds very interesting--------------

Thanks,
Grampa

Well it seems we had some forum difficulties today. Things seem to look a little funny but running again. Glad I found your post as there was no email notification. Anyway....

A 12 volt 1 watt LED will draw about an amp. Would these be some type of super bright LED as that is pretty high current. So what you have is a sount that triggers a sound activated module and that module blinks a LED. You want that little LED to in turn trigger some much larger 12 volt 1 watt LEDs.

One option would be to use as I mentioned a small opto coupler. Yes, what an opto coupler really is in simplified terms is a tiny LED embedded in a case with a small photo sensitive transistor. They are isolated from each other in the same small package. Give me a day or so and I'll put together a small circuit that should do as you want. The parts should be readily available and very inexpensive.

Ron

Excellent,
Now we're talkin'
(Yes - the LED's are mega bright straw hat type - 140 degree illumination)

Thanx

Attached is a circuit that should get you where you want to go with this. You have a tiny LED on a module and want to drive a few high power LEDs that have a forward current of about 1 amp @ 12 volts. That creates a few things to overcome. There may be other ways to go about this and hopefully another member will chime in. While I have not assembled and tested the attached design it does seem to work well in a simulation.

You would remove the existing led and run two wires in its place to the 4N25 opto coupler. In the drawing V1 is only there to simulate the signal you have from the existing LED and V2 is the 12 volt supply.

In a nutshell the opto coupler is turned on and off by your existing signal. The output of the opto drives Q1 through diode D1 and resistor R1. Resistor R2 serves as a pull up. Q1 in turn drives an IRF510 common MOSFET. Acting alone Q1 would not be able to handle the load of the super bright LEDs you have. The MOSFET M1 does the current handling. LEDs D2 and D3 are just representative of your LEDs and resistors R5 and R6 limit their current for the LEDs I used. This assumes your LEDs have their own on board current limiting resistors and are designed for 12 volts applied. If you have a link to the data sheet for your LEDs we can check that out.

So what you have is a start.

Creedmore NC huh? Every May (Memorial Day Weekend) I head down to Winston Salem and also visit Carey NC to see old friends I grew up with in NYC who settled down there. These are friendships spanning over 50 years. I always look forward to what the wife calls "The annual Ron trip". This is a trip she does not make.

Ron

Thanks for the schematic. The current limiting resistors are 330 ohms so that's under control.

I am an escapee from White Plains and have been for 35 years, and my son lives in Cary - small world.

I'll let you know how this Rube Goldberg contraption works out.

Yeah, small world.

Then you know the difference between a Yankee and Damn Yankee. A Yankee goes down south, spends money and returns to the north. A Damn Yankee goes down south, likes it and moves there. Future plan may have me being a Damn Yankee. I may become one of the latter as retirement looms. Then too, have the grandchildren up here. Best gift my kids ever gave me.

Ron

By the by,

CARY stands for Containment Area for Relocated Yankees.

You can hardly find a southern accent down there.

Yeah. I knew that. I tease my friend Val that they even have monogrammed trash cans with the little city seal.

Have a great day....
Ron

I would like to use the 1 vdc that is lighting the led

Click to expand...

The voltage to light a LED (its forward voltage) is normally ~ 2V at least. How is the 1V being used at the moment to light the LED? If the 1V is externally accessible and can source at least 5mA then all you need to drive 2 x 12V 1W LEDs is a 100 Ohm resistor and a ZTX1049A or similar NPN transistor, plus any necessary current limiting resistors for the 1W LEDs.

A 12 volt 1 watt LED will draw about an amp

Click to expand...

Eh? If the forward voltage of the LED were 12V (which I doubt very much) the current would be 1W/12V = 1/12 A, i.e. ~ 83mA. Let's assume (in the absence of the OP's datasheet) that the forward voltage of the LED is 3.6V. The max current will be 1/3.6 = 280mA. So a ZTX1049A would easily drive several 1W LEDs.

Looking at this now I likely blew it big time. No clue how I got that amp other than screwed it up and never looked back. I also assumed (bad on that) the existing led is in reality around 1.8 to 2 volts so went with the opto coupler idea. The data sheet would have been nice.

Many thanks Alec for wandering in and catching my screw up. I hope the OP gets back in here and am pretty sure he will.

Ron

Please help me come up a SIMPLE solution to this problem.

Click to expand...

If the 1V really is 1V (and not an average, because the LED is blinking) here's a simple solution. If the '1V' is in reality a pulsed 2V signal (or thereabouts), R1 should be increased to, say, 330 Ohms.

Yep, I'm here,
WOW !
That circuit looks really simple !
Here's some more info that might help.
The little module that is producing the one volt (maybe two as my fluke vom probably isn't fast enough to record) is powered by 2) 1.5v button cells.
The 1 watt Led's have a forward voltage of 2.2 to max 2.4v, forward current 300ma, and the limiting resistor for operation by 12 vdc figures out to be 330 ohms.


Thanx,

Sorry on my bad. Just run with the simple circuit that Alec provided as it will do just fine. I let myself convince myself you needed 1 amp per LED. really dumb on my part. The transistor used is a good choice but any number of NPN types used as a switch will work including the 2N2907 which is likely more common. I don't know the switch (on/off) rate. If we assume a Vf of 2.3 mA and a If of 300 mA it works out as I supply of 12 volts - Vfwd of 2.3 volts = 9.7 volts / 300 mA = about 33 ohm series resistors with the LEDs. That is one resistor per LED. Even a 36 ohm would be a good choice to limit the LED current.

Again, sorry I blew it on that.

Ron

Not sure where you got the 330 Ohm figure from for the LED series resistors. I agree with

12 volts - Vfwd of 2.3 volts = 9.7 volts / 300 mA = about 33 ohm series resistors with the LEDs.

Click to expand...

However, that's if you want to run the LEDs at their maximum rating. Personally I'd use 39 Ohm (or even 43 Ohm) resistors, so that the LEDs aren't stressed.
As Ron says "any number of NPN types used as a switch will work". The 2N2907, though, is marginal as its max current is only 600mA and its gain is only ~100. We don't know how much current your '1V' input can provide, which is why I suggested the ZTX transistor as it has a gain of 300 and hence needs less base current to drive it.
Now that we have the LED specs, I'd make R1 = 330 Ohms if using a high gain transistor such as the ZTX one.

Thanks guys,
I'll let you know how it works out.................

An even simpler circuit is possible if the two LEDs are in series. It saves on one resistor and has the advantage that a wider choice of transistor (including the 2N222A) is available, as the total current is halved.

THAT'S IT !
Thanks a lot, ALEC and RON !