LED Light Box Troubleshoot

[CDRIVE]

Velleman MK103 with 2 blue LEDs in place of the 4 red ones or connect it to a 12V supply and replace the LEDs with a MOSFET to drive your strips.

http://www.vellemanusa.com/products/view/?id=350678

I doubt that he'll get enough Gate voltage to drive a power MOSFET directly from his IPad's audio. Maybe I'm wrong?

 

[KJ6EAD]

OK, I read the sales data the link you posted. They say that their led strips can be cut at every 3 led cut point which they say is about 1" segments. If they're 3 led segments I think the circuit would look like this, which is a series parallel circuit. If anyone is familiar with these strips and thinks I'm mistaken please speak up.

That's exactly how they're wired, small bused sections. They were originally designed to be installed as backlights in signage as a replacement for neon so they had to be easily field configurable by installers on ladders and bucket lifts.

I doubt that he'll get enough Gate voltage to drive a power MOSFET directly from his IPad's audio. Maybe I'm wrong?

You're right but the MK103 and the MK186 both use a microphone input. They would have to be modifed to take a line or headphone level input.

He?! Desirae is usually a female name. We see a small enough percentage of forum members that identify as female by name or profile that we should notice when they come around.

 

[Desirae]

Velleman MK186.

http://www.vellemanusa.com/products/view/?id=525680

Now that looks promising!

I can attach that to the 12v adapter I took off an old phone and hook up the led strip directly?

 

[Desirae]

You're right but the MK103 and the MK186 both use a microphone input. They would have to be modifed to take a line or headphone level input.[/QUOTE]

I'm ok with the microphone picking up the sound instead of direct input of the audio. I was doing it that way because of the instructable and the fact that I had lots of those bits already on hand. If the MK186 can be hooked up to an old 12v adapter and use the light strip, that would be great

 

[Desirae]

He?! Desirae is usually a female name. We see a small enough percentage of forum members that identify as female by name or profile that we should notice when they come around.[/QUOTE]

Yes, female. But not offended

 

[KJ6EAD]

Now that looks promising!

I can attach that to the 12v adapter I took off an old phone and hook up the led strip directly?

Yes, as long as the 12V supply is reasonably well-regulated. Is it light and sort of flat or squarish and heavy?

Yes, female. But not offended

You will now be hit on... er... receive 86 friend requests from nerds.

 

[Desirae]

Yes, as long as the 12V supply is reasonably well-regulated. Is it light and sort of flat or squarish and heavy?

Light and sort of flat...
But I'm sure I have one of those blocky ones around here somewhere if you think it would be better suited?

 

[KJ6EAD]

The light ones are the more modern switch mode power supplies. They are more efficient and usually well-regulated so use that.

The older electromagnetic power supplies will often run several Volts above their nominal rating when lightly loaded which could shorten the life of your LEDs.

 

[Desirae]

Ok I will.
I have been looking at the MK186 and it looks like something I can manage. I was hoping not to use a kit as a matter of pride, but this project has bested me.

 

[KJ6EAD]

Tangible results and the realization that you've expanded your knowledge and skills beyond previously assumed limits should be a sufficient pride preserver.

Post a link here to a short video of your completed project if you can when it's done.

 

[Desirae]

Too true

 

[(*steve*)]

Tangible results and the realization that you've expanded your knowledge and skills beyond previously assumed limits should be a sufficient pride preserver.

True. I would look at it as an "informed choice".

No shame in being able to spot a good solution and knowing when to change horses.

 

[CDRIVE]

Ok I will.
I have been looking at the MK186 and it looks like something I can manage. I was hoping not to use a kit as a matter of pride, but this project has bested me.

The benefits of kits like that usually far out way the desire to build from scratch.

No scrounging up the components from multiple suppliers.
No excessive shipping costs do to multiple suppliers.
The kit is typically cheaper than the cost of the individual components.
Best of all.... You don't have to make the PCB!

 

[CDRIVE]

Desirae, are you still interested in building this from scratch using your TIP31?

 

[Desirae]

Desirae, are you still interested in building this from scratch using your TIP31?

Yeah, even if I do end up going with the kit, I would love to figure out what I'm doing wrong here.

 

[CDRIVE]

OK, I messed around with the TIP31 but abandoned it for a power FET. I did get a working model with the TIP31 but it's inferior to a power FET for this application.
You can Google the OPA134 and the IRF510 data sheets for specs on these components.
I chose the IRF510 only because it's common. Others may suggest better alternatives. The OPA134 is a high performance, single ended supply, wide band OpAmp. You can purchase them in a single or dual amp (DIP) package.

If you want an Electret Mic version of this circuit I'll post it for you.

 

[(*steve*)]

Nice.

With a couple of resistors and a transistor you could provide a current limited output that would then be ideal for strings of LEDs that don't incorporate resistors. You would also increase the gate resistor - which doesn't need to be this low since rapid switching is not necessarily what we're after.

You would place a current sense resistor in the source, the emitter and base of a small NPN transistor across it (emitter to ground, base to source) and tie the collector to the gate. As the drain current increases so that the current sense resistor drops 0.6V, the transistor turns on, robbing current from the base, thus lowering the voltage and turning it off a little.

The slight negative feedback caused by the source resistor would not dramatically alter the performance of the device.

 

[CDRIVE]

Steve, if Desirae is driving a few Led strings then that's quite doable but if she wants a high current light show, that's a different ball game. I designed this circuit to keep Q1's rDS(ON) as low as possible. Creating feedback to pull the Gate voltage down will put Q1 in a region above rDS(ON) and closer to it's Vgs(TH), which is counter productive and would cause Q1 to dissipate excessive wattage. Q1 is rated @ 5.6A continuous @ 25 deg C and 20A pulsed. However, we all know that these ratings are valid @ rDS(ON) only.

Desirae said that each LED segment has an integral limiting resistor in groups of three series LEDs, so I don't think current limiting will benefit her in this application anyway.

 

[(*steve*)]

True, won't help in this case. And certainly true in terms of power dissipation.