HELP! 12V light controller

[weekendshock]

Hi,
I am trying to power a 12 volt-6watt LED lamp that comes on a dusk and goes off at dawn. Long story, but I had a circuit that a friend built several years ago.
It consisted of a photo resistor, Schmitt trigger, 2N2222 transistor, 50K ohm trim pot and a 1K ohm resistor.
The Schmitt is triggered it closes 2n2222, which closes ground to lamp which is discrete from power ground. The transistor is supposed to open and close the ground leg going to the lamp, which it does. My problem is the transistor becomes very hot and soon fails. This circuit worked excellent in the past with these components and I am trying to duplicate with limited success.
What I am doing works. If I can get the transistor to stop overheating I will be fine.
I know you are probably laughing because this is so simple to you, but it is way over my head and any assistance would be so appreciated.
Thank you,

 

[MikeMl]

Trace and post a schematic

 

[KeepItSimpleStupid]

You may not be turning on the 2n2222 hard enough. What's the voltage across C & E when the lampis on? It's only good for 800 mA tops and I would not be using it at it's limit. I'd suggest another transistor number such as a TIP30.

 

[weekendshock]

Hi Mike and KISS,
Thanks for getting back to me. I have thought about using a different transistor to overcome this problem, but this used to work using these particular components even when it was over 100 degrees all night long in Arizona. I remember the person that built the original one told me that to make the Schmitt trigger stable, you hade to connect the unused legs together. I do not know how to do this and suspect this may be the problem. Since this worked so well in the past I know it can be accomplished again.
The circuit that I have assembled works, but the transister gets hot. I remember that the original one had a metal can 2N2222, I am using the black plastic like ones. Could that be the problem. I have tried to attach the schematic. I hope it comes through.
Much thanks guys for anything you can come up with.
Jim

 

[KeepItSimpleStupid]

The package type makes a BIG thermal difference. The plastic package connot dissipate as much heat as the metal package.

 

[weekendshock]

Hi,
Thanks. Does this circuit look good to you? Can you tell me which legs to connect together or omit? I know that leg one and two are one of six triggers and that is the one I am using. Number seven is ground and number fourteen is +V. What do I do with 3,4,5,6,8,9,10,11,12, and 13? As said earlier, it seems that I was told they had to be linked together somehow even though they were not being used.
Thanks again for any directions that you can provide.
Jim

 

[colin55]

Use a TIP darlington

 

[audioguru]

The CD40106 has six Schmitt trigger inverters inside. Your circuit is using only one to supply not enough base current to the transistor and is throwing away 5 inverters that could make the base current 5 times more.
The circuit should use one inverter to sense the photo-sensor and the remaining 5 inverters should be in parallel for 5 times more base current.
You would need to swap the photo-sensor with the resistor in series with it.

 

[weekendshock]

Increasing base current

Hello Audioguru,
I am a total novice when it comes to these things. (could you tell?) lol
Can you please be very specific with your instruction as to how I go about paralleling the other five triggers?
I know that 3, 5, 9, 11 and 13 are in and 4, 6, 8, 10 and 12 are out.
At present, I am using 1 and 2 as my triger and have 12V going to leg 3 and five. I also have 9, 11 and 13 linked together with a piece of wire. This is how the first circuit was built as far as I can tell. I am not using legs 4, 6, 8, 10, 12 and also 14 which is 12V in.
I have leg 1 hooked to center (#2) leg of the trim pot and leg 2 to the base of the transistor. I have the collector hooked to power ground and the emitter hooked to lamp ground which in effect makes or breaks the ground leg for the lamp.
As I said before, I am total novice when it comes to electronics so if you could step by step me through what connects to what as far as the Schmitt trigger configuration, I would be most greatfull.
Thanks so much for your time and knowledge.
Jim

 

[Reloadron]

I believe what AG is suggesting is make the circuit like the attached image. Since it is an inverting Schmidt trigger we reverse the location of the pot and photo cell, then we parallel the remaining five inverters and use all 5 to drive the transistor.

Ron

 

[KeepItSimpleStupid]

Yep, good move.

The rule is that unused inputs for this logic family have to be tied to Vcc or Ground or else you risk the IC oscillating and overheating. Paralleling the inverters in this case is an even better choice.

 

[weekendshock]

Hi guys,
Especially, AG, KISS and Ron for his beautifull schematic.
I really appriciate all the time and help you are providing to help me. If I understand this correctly, I need to tie all odd numbered legs together and all the even numbered legs together except for # 1 and 2 which of course are being used. I feed the odd numbered buss with #2 and the even numbered buss to the base of transistor. Is this correct?
I do understand about switching the resistor, trim pot and LDR posistions, but I just want tyo verify connections on the 40106.
Can't express my appreciation enough. This is apparently simple for you guys, but for a novice, kinda like walking to the moon. Good News, I am starting to get it, just a little more hand holding and I think the light will come on! haha
Regards,
Jim

 

[audioguru]

I think the 2N2222 or the CD40106 will overheat without a current-limiting resistor between them.
Why is the supply as high as 12V? To fry something in the circuit?

 

[weekendshock]

LDR light controller

Hi AG,
I run this in my RV to keep "Old Glory" illuminated all night. Of course my rig is 12V so it is Run What Ya Brung. I am giving one of these to my Sister and Brother-in law for Christmas and I am going to drive it with a transformer. 115V-800Ma dc out.
Are you suggesting that I put a resistor in line to drop voltage input to this circuit?
I am fine with that as long as it does not draw any more from my batteries while it runs all night in my camper.
I, as you already know am not a player when it comes to electronics and their design. Now you have thrown another wrench into the gearbox! Way to go pal. Just kidding. Anything you can think of that would make this more reliable would be most welcomed.
What do you suggest? Please keep in mind that I would not want any more precious power extracted from my battery than what is needed to keep my flag lit all night.
I am not as concerned of course while running a transformer on grid power.
Looking forward to hearing from you soon,
Jim

 

[audioguru]

Are you suggesting that I put a resistor in line to drop voltage input to this circuit?

No.
I suggested adding a series resistor from the outputs of the C40106 to the base of the transistor to limit the current so they don't blow up.

I would not want any more precious power extracted from my battery than what is needed to keep my flag lit all night.

You are using an old fashioned light bulb where 90% of the battery energy makes useless heat and only 10% of the battery energy makes light.
If you use a couple of high power LEDs then most of the battery energy makes light.
The battery will last much longer or you can have much more light then the battery will last as long as with a light bulb.

 

[weekendshock]

Hello A.G.
Can you suggest an appropriate resistor? I can of course add one, but would have no idea as to the proper value that would limit current by the proper amount.
This is a small circuit , approx. 1" X 1" and must fit inside of a weather-proof enclosure that I selected. Adding one more resistor should certainly be doable as long as it is no more than about 1/2 watt.
BTW, Why is it better to reverse the order of LDR and the two resistors? I will reconfigure my circuit to match what you are recommending and follow the schematic that Ron sent me, but for the sake of understanding and learning, I cannot understand why this is better because the circuit works with photo-resistor first in line and the resistors going to ground.
Jim

 

[weekendshock]

Hi again,
Didn't see the rest of your reply until just now. Yes, I am using a 3watt led lamp. It is 3X1 watt at around 6000K, works fantastic, draws very little, runs quite cool even in water-tite enclosure and has long life. It runs all night and only brings my batteries (I have two deep cycle group 31, 12's in parallel) down about 1/10 of a volt. This is very acceptable and I would not like to keep this light controller with low power comsumption in mind. I would run two six volts in series, but I do not have the room and therefore not possible.

 

[audioguru]

A white LED needs about 3.5V. Its current must be limited. If three are in series then they need 10.5V plus current limiting.
But you showed a 12V light bulb instead.
What limits the current to your LED?

 

[weekendshock]

It must have limiting built into it because I can hook it up to a twelve volt car battery and it runs just fine. I also have a transformer that is 12.5 volt dc, 800mA and it also runs fine when I power it directly from that. I am going to use this when I light the flag on the house and is the reason I am building the light controller, so it comes on at dusk and goes off at dawn.

 

[audioguru]

Then we are just guessing about its current. The part number for the transistor, the value of its base resistor and the size of the battery depend on the amount of current for the LED light.