RGB LED controller current extension

[Walter6540]

Hello everyone.
My project is to extra RGB LED arrays and use extra current power extension for regular low power RGB LED controller. I would like to use TIP 3055 transistors according to diagram. Will that solution work for
color light shows? Thank You.

 

[AnalogKid]

The circuit will not work as shown. Either the transistor collectors stay connected to +12V and the LEDs get connected to GND, or the LEDs stay connected to +12V and the transistor emitters get connected to GND. The actual changes are a bit more complex than that.

But first, two very important questions: Before adding the three transistors, how were the LEDs connected to the controller? Also, what is the maker and part number of the controller?

ak

 

[Walter6540]

There is no brand name or part number. I uploaded connection diagram and
a picture of controller board.

 

[AnalogKid]

According to the user manual for your device, there needs to be a resistor in series with each LED string. This tells me that each output is a saturated N-channel MOSFET switch that is pulse width modulated. You cannot drive a TIP3055 with this type of output to do what you want. What is the writing on the three power transistors to the right?

If you have access to P-channel power MOSFETs, maybe they can be adapted to work.

ak

 

[Alec_t]

What is the writing on the three power transistors to the right?

09N03 indicates they're N-channel MOSFETs, so they're presumably low-side drivers for the LEDs.

 

[AnalogKid]

Given that the board has dual footprints, one option is to remove the standard FETs and drop in big fat boys. The problem is the 24 A of ground current.

ak

 

[Walter6540]

Maybe I can remove FETs, install something like FQD13N10TM 10Amps current
on separate board, connect powerful MOSFET gate to controller board instead of old one and connect Source directly to power supply and load to Drain

 

[AnalogKid]

That's the basic idea (no warranties expressed or implied). I'm assuming that the controller can dim the LEDs, and uses PWM to do it. If so, then the new FETs have to be fast enough to keep up. Might be a problem because a large MOSFET has a large gate capacitance, and needs a gate drive circuit that can charge and discharge it fast enough to keep the FET out of its linear region when the big current is flowing. I couldn't find a datasheet on the controller chip, so this approach is a bit of a gamble.

Before any mods, operate the controller for a while with 2A loads and feel the original FETs to see what the designers think a reasonable operating temp is. Then you'll have a starting point when the new FETs fuse your fingerprints.

ak

 

[Walter6540]

I have the same controller made by different manufacturer and there are FDD 8880
transistors used and datasheet link is here
https://www.fairchildsemi.com/products/discretes/fets/mosfets/FDD8880.html

 

[AnalogKid]

Nice part. There still is the issues of 24 A currents running around. If the three FET sources go through pc board traces to an external connector pin, you might want to add some #16 solid wire in parallel to the traces for lower resistance.

ak

 

[Walter6540]

There is only one color or combination of colors are on in one time frame.
Only one channel is open or a combination of channels with current equals about
of 8 Amps at the time. I measured the current after the controller with 10 pieces
10 watts RGB LED in parallel load and Imax was 3.3 Amps. Now I would like to increase the load up to 22 pieces 10 watts RGB LED and I assume the current will be up to 8 Amps. I sorry for some misrepresentation of my project.

 

[Walter6540]

I connected 10 pieces 10 w RGB LED http://www.ebay.com/itm/25132142917...49&var=550678555489&ssPageName=STRK:MEBIDX:IT directly to the controller. Is there better to use a resistor in series to limit
the current? It worked for a few months, no issue.