Boosting current on a circuit?

[Revenant]

I wanted to use multiple LEDs on a flicker circuit (or at least substitute high-intensity ones which are about 30 mA) but didn't know if it could handle the juice. I emailed the distributors of the ICs and they responded:

10 to 20mA output current. Therefore it can drive one LED only. If you need add more on the circuit, you must add a transistor to boost up current.


Okay, transistor. Now, what kind and how do I add it to the circuit to boost the capacity? The ICs have 3 leads; Pos, Neg, and a third I'll call L-. the battery attaches to Pos and Neg (duh) and the LED hooks up to Pos and L-.



So, all you high-tech whizbangers out there... couldja help a poor Luddite out? I think a fire-flickering LED spot could come in SOOOOO handy....!

[heresjohnny]

Hey Rev, I think this will work. I use something like this to drive LEDs of a low power op-amp. This should be good for up to 100mA. You can use a 2N2222 also for the transistor, that will get you up to about 500 mA. I think I have the leads right, hope it works!

[heresjohnny]

I think I need to clarify a little.

Get a transistor, (I have used a 2N3904 and a 2N2222) and look at the package to see which lead is the Emittor (E), the Base (B) and the Collector (C).

Carefully solder the Base of the transistor to L- lead of your thing. Solder the Emitter of the transistor and the negative lead of your battery to the (-) lead of your thing. Twist together and solder the Collector of the transistor to one side of a 470 ohm resister. Solder the Emitter of the transistor to cathode of the LED (the side of the LED with the flat edge and the shorter lead) to the other side of the 470 ohm resistor. Solder the Anode of the LED (longer lead) and the positive battery lead to the (+) on your thing.

If you want, PM me, and I can send you my address. You can ship some to me and I can wire em up for you and take pictures!

[Revenant]

Thank you johnny! Especially for the second post -- handing me a schematic is like handing a CD to a deaf person; I need electronic instructions to be pretty explicit lol

When my LED's I'm bidding on come in I'll try to wire up an LED spotlight to one of these ICs and see what happens. I think having a mini-spot that throws firelight could be mighty useful. And a JOL would show up much better if several LEDs were flickering inside at the same time. This may be a bit ambitions for someone like me who knows Jack Shi(r)t about electronics but I guess I gotta learn somehow lol

[heresjohnny]

Originally Posted by Revenant

Thank you johnny! Especially for the second post -- handing me a schematic is like handing a CD to a deaf person; I need electronic instructions to be pretty explicit lol

When my LED's I'm bidding on come in I'll try to wire up an LED spotlight to one of these ICs and see what happens. I think having a mini-spot that throws firelight could be mighty useful. And a JOL would show up much better if several LEDs were flickering inside at the same time. This may be a bit ambitions for someone like me who knows Jack Shi(r)t about electronics but I guess I gotta learn somehow lol

The 470 ohm resistor takes the place of the resistor that you usually put in an LED spotlight. Also, I have used hot glue on the tip of the ultrabright LEDs to act as a diffuser, and I have read somewhere (in HauntForum I think) about using clear silicon to do the same thing.

[gmacted]

Revenant,

What are you using for source voltage?

Depending on your source voltage and the circuit, you may be able to put a couple of 20 mA LEDs in series with this circuit. LEDs in series will draw no more current, but the forward voltage drop will be the limiting factor.

Do you have the specs for the high intensity LEDs you wnat to use? The important specs are the forward voltage and the forward current.

Heresjohnny's circuit will work fine, but you will want to customize it for the number of LEDs you want to use.

Are you running these circuits using wallwarts? If not, how you configure the circuit will save battery life and allow you to run the circuit for a longer period of time using a battery.

This may be a little confusing, but I'm just trying to help (really).

[Revenant]

The specs on the LEDs are thus:

* Emitted Colour : White
* Size (mm) : 5mm
* Lens Colour : Water Clear
* Peak Wave Length (nm) : N/A
* Forward Voltage (V) : 3.2 ~ 3.8
* Reverse Current (uA) : <=30
* Luminous Intensity Typ Iv (mcd) : Average in 13000
* Life Rating : 100,000 Hours
* Viewing Angle : 20 ~ 25 Degree
* Absolute Maximum Ratings (Ta=25°C)
* Max Power Dissipation : 80mw
* Max Continuous Forward Current : 30mA
* Max Peak Forward Current : 75mA
* Reverse Voltage : 5~6V
* Lead Soldering Temperature : 240°C (<5Sec)
* Operating Temperature Range : -25°C ~ +85°C
* Preservative Temperature Range : -30°C ~ +100°C

As you can see even one of these guys would probably send the poor IC to Silicon Heaven. Johnny said the 2N2222 transistor would support up to around 500 mA so that's what I'd need to drive one of his 7-lamp spots.

As for power supply, I don't know yet. He made his steady spots to run off a 9V battery, which would be cool, but the IC can only handle about 4.5V so I'm sure 9V would let the blue smoke out. The optimum voltage for the LEDs is around 3.5 anyway. I'd either need a rather beefy spotlight body that could handle 3 batteries or can I step down the voltage of the 9V with something small enough to fit in the little PVC tube? Otherwise I'm pretty much stuck with running a line to a DC power supply.

I think the thing that's cool about battery powered spots is they'd be better for outdoor use; no extra wires to route and trip over or power supplies to weatherproof. And at night you can just collect them and bring them inside without disconnecting anything.

[heresjohnny]

What spotlights are you using? How is the array configured? Driving a 7 led spot is different than a single LED (what I thought you were doing). Gmacted is right about tuning the circuit.

[Revenant]

Well, the spotlights I had in mind were the ones on your http://www.johnnyspage.com/ledspothowto.htm page. Although you show the actual making of a 5-lamp spot using parallel arrays of 2, 1, and 2 lamps, you also had a great pic of lighting from a 7-lamp spot using the same size LED's I'm getting. I think the stronger light would be good for a firelight source.

Using linear's calculator, the only circuit I can use if I use a 4.5V power supply is a completely parallel circuit, 7 branches each with its own resistor. If I used a 9V supply it could give me a 4-branch series/parallel circuit that would not only save on components but draw less current (120mA instead of 210 for the completely parallel one). But 9V would smoke the IC so that's out. Using the series/parallel configuration I'd have to use a separate flicker IC for each branch and that won't do because all the lights have to be in synch.

So... I guess I'd have to power it with 3 regular batteries (I guess I could use AA's and put them in a flat base). An alkaline AA battery averages 2700 mAh so with a drain of 210 mA I guess that's about 12 hours of use... if it were a steady spot. But technically it should be less drain because the IC is ramping the intensity of the LEDs up and down so they're not full-on the whole time, so they should last longer than that. Dunno. Whatcha think?

And... since you thought I was just using a single Hi-brite LED at first, you put that 470-ohm resistor in that circuit you drew. Do the resistors in each branch of the circuit from linear's calculator take the place of that? So I just connect the collector of the transistor to the cathode node of the LED array?

[gmacted]

The small circuit is most likely a 5V circuit, but will operate at 4.5V (three 1.5V batteries in series). You could use a 9V battery and a LM7805 (5V regulator). The output of the regulator (5V) would be used to power the circuit and the 9V would be used to power the transistor/LED portion. A 2N2222 transistor can handle 800 mA (maximum collector currrent). You could easily operate 25 high intensity LEDs using this transistor. The only problem here is the more LEDs you use, the more current you will draw and the shorter the time the circuit will operate. An alkaline battery can source ~580 mA hours. If your circuit is drawing 100 mA, the battery will last ~ 580Ah/100mA = 5.8 hours. If you draw 200 mA, the circuit will only operate ~2.9 hours. These values are only approximate and will most likely last longer, but it gives you a ballpark figure of how long the circuit will last.

I built a flicker circuit with three high intensity green LEDs that operates on a 9V battery. I got the circuit to run almost two days using one 9V battery.

You need to make some decisions before you can move forward.