Amplify current of a flickering candle LED

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ThomsCircuit

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Greetings. I while ago took 9 flickering leds, connected them in series (3x3), obscured them with frosted plastic, and supplied 12v. At 3 feet they were pretty bright and you can see some flicker but from a distance of 10 feet or more its not so defined. So ive learned a little and want to give this another go.

I have been reading about using a transistor to enhance or amplify the effects from a flickering led. I settled on this one. The author had this powered with 3V and said it worked well. I want to adapt this for 12V but need some assistance. I bread-boarded the project and all leds illuminate. the flickering led flickers but the others do not. Its possible that i have the wrong resistor values for R1-R3. Can you help me get this project working correctly?

 
I think each led will see 2.4 volts and 5 mA of current. What are the specs on the flicker led?
 
I finally got this one to work. Its been about 6-7 months since i have tried. My BBoard skills must have improved as it worked on the first try. My speaker sounds like a tin can though. Its a piezo but i'm not interested in using this circuit for that reason. Just to amplify the flicker and the LED connected to pin 3 of the 555 does appear to react to the flickering leds pulses.

I still want to get the first schematic working as i just might learn something in the process.

 
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Lightium said:
Are you familiar with spice simulators?
Click to expand...
yes. i have tried to understand how to use them. I am so bad with formulas. I just do not know enough about caps, resistors, and current to be able to use it properly. I do the best I can to figure things out myself and i come here when i am stuck. but on the bright side I am better than i was last year.
 
A theory i had about why the schematic in #1 lights but does not flash could be that it IS flickering but that its happening to fast for me to see.
 
rjenkinsgb said:
Try reducing R1 a lot, say 1K?

That would give about 10mA to the flicker LED. With 33K, it only has a fraction of a milliamp, possibly too little to work.
Click to expand...
I think that you are correct that R1 needs to be reduced, but it may need to go lower than 1 kOhm.

You only need about 70 Ohms for 10 mA to give enough voltage to turn on Q2, because that will happen when there is about 0.7 V between the base and emitter of Q2.

I'm not familiar with the flickering LEDs, and I don't know if they need a series resistor or not. If they need a series resistor, then it you can't reduce R1 too much. If the flickering LED needs a series resistor, disconnect the cathode (-ve) of the flickering LED from ground and put a suitable series resistor between the cathode of the flickering LED and ground. You can then adjust the value of R1 to any value you want.
 
I don't completely understand this. there may be a typing error but it did make me realize WOW, ive got an led on 12v with a 33K resistor and it still lights. How is that? Regardless I changed that to 1K and the circuit was unchanged. I then began lowering the voltage and at 6 volts the circuit began to function as designed. the flickering led was dim but the other leds danced brighter. If it helps im quoting the authors explanation here

"The flickering effect is produced by a pulse width modulation (PWM) circuit, internal to the special LED. Each time that LED circuit turns on, current is drawn through the 560 ohm resistor R1. The voltage drop across the resistor is enough to turn on the 2N3906 PNP transistor. That transistor then produces an identical PMW signal at the collector, which swings over the full 3v peak to peak voltage. The collector signal is then fed to the gate of a ZVN4306 n-channel MOSFET. Acting as switch, the transistor routes current through 5 super bright yellow LEDs. Each LED has a 47 ohm resistor to limit the peak current to about 20ma. A fresh pair of 1.5v alkaline Dcells should be able to power the touch light for about 8 hours."

Now I did contact the author and he responded to my request for help in adapting it from 3v to 12v. He replied with the recommendation of the 33k resistor (original was 560r) and that my mosfet was fine.

I would like to know why the circuit performs like it should for 6V but not for 12v and if we could, get it to work with 12v. the goal here is to take a flickering LED (which is not very bright) and pass its output to regular LEDS that are much brighter.
 
ThomsCircuit said:
all leds illuminate. the flickering led flickers but the others do not
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Do you know if the LEDs are getting any PWM signal, or are the on because Q1 and/or Q2 are saturated?

Instant analysis based on very little information . . .

Because Q2 is supposed to operate as a saturated switch, a very small minimum continuous current through D6 will keep it on all the time. And there must be a small continuous current through D6 to power the flicker control circuit. Q2 amplifies that small current by 100x, and pushes that through R2.

Let's say it takes 2 V Vgs for FET Q2 to sink enough current for the main LEDs to come on. That is a minimum current through R10 of 200 uA, and that is a base current into Q1 of 2 uA. So, if the minimum continuous current through D6 is high enough that even through a lot of it comes through R1, at least 2 uA comes through R3, the main LEDs will be on.

Something else to consider -

D6 has a minimum operating voltage requirement, below which it is off all the time. And Q2 has a minimum Vbe of around 0.5 V for any useful collector current. When running on 3 V, this leaves a small range of voltage across R3 for circuit operation, but that range is a significant percentage of Vcc. As D6 goes on and off, the voltage across it goes up and down, modulating the current through R3 up an down around the 2 uA trip point for the output changing state.

Change Vcc to 12 V, and everything changes. The ratio between the voltage drop range across R3 for operation and Vcc is now probably 10x what it was at 3 V. Because that operating voltage range now is such a small percentage of Vcc, finding the R1-R2-R3 sweet spot for circuit operation will take some tweaking.

Starting point - replace R1 with a 100K pot, and see if any value of R1 will work with R2 and R3 at 10K. A scope across R1 will tell us lots.

ak
 
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If you tell me the flickering LED’s part number, I can breadboard the circuit and provide waveforms.
 
ThomsCircuit said:
Regardless I changed that to 1K and the circuit was unchanged.
Click to expand...
OK, try adding a pot or preset across the 1K (e.g a 4.7K or 10K), with R3 connected to the wiper.
That should allow you to find an appropriate bias point for the transistor?
 
AnalogKid said:
Do you know if the LEDs are getting any PWM signal, or are the on because Q1 and/or Q2 are saturated?
Click to expand...
no i do not know. I dont think they are and i base that on I have no way of knowing.
and even though i do not know how to calculate this i understand 100% of what your saying. Its a good thing. Why did i not pay attention in algebra! Understanding formulas
OK i will do this. AND im going to invest in a beginners scope for hobbyist.
Thank you so much.
 
rjenkinsgb said:
OK, try adding a pot or preset across the 1K (e.g a 4.7K or 10K), with R3 connected to the wiper.
That should allow you to find an appropriate bias point for the transistor?
Click to expand...
ok i have a 20K pot and connected as follows.

with this setup at 5V i slowly adjust the pot and the voltage until the 5 leds no longer react to the flickering led. The best I could get was 7V with the pot at 56R. Any more voltage and the flicker led would blow.
 
AnalogKid said:
Ummm ... your profile says this:
Area of Specilization: 1. Analog IC Design
How does that work?
ak
Click to expand...
Total Noob was unavailable. I had to choose something. But that was years ago. Now with my experience and knowledge i could add Poo Fingers to the list.
 
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