picprojects.org.uk

Hia, just bought one of these kit's can't wait for it to come, gonna get a bucket load of thoes Piranaha RGB LED's, they seem to work very well for you.
Just a few questions;
The output voltage of the driver, it is the same as the PIC dictates isn't it? i.e. somewhere between 0VDC and 5VDC?
Have you any rough idea how many Piranaha LED's I can run off this board (max). Doing some DIY bathroom mood lighting.
And does the number of LED's change the resistor values of each LED, or are they pretty much the same as what you have, 68r for the red and 47r for the green and blue.

Thanks for all your time and a great project site, Carlos

If you look at the schematic you will see the MOSFETs drive the LEDs essentialy from an open drain so the voltage is nothing to do with the supply voltage to the PIC. It is the supply voltage to the board which other components dictate to be a maximum of 24 volts (minimum of 9 volts)

If you use a common anode RGB Prianha LED then you cannot connect them in series so there is not advantage to using a high input voltage.

The prototype controller shown with the Piranha LEDs didn't have an onboard 5 volt regulator, it was fed from an external 5 volt supply and the resistors for the LEDs were calculated accordingly.

The Power MOSFET driver on the webpage has it's own 5 volt regulator for the PIC, which means the input voltage to the board must be a minimum of 9 volts. Typically you will use the power supply feeding to the input to the board for the LEDs so you will need to calculate the resistor values for the LEDs acording to their forward voltage, desired operating current and input voltage.

DO NOT assume the values I've used with the prototype will be suitable for your application, they won't

This is all explained on the webpage and there is a link to a LED resistor calculator.

Thanks for clearing that up pete. Just taken a much closer look at the board layout and completely get what I need to figure out now. Gonna have a 12V transformer feeding the board and LED's, that LED calculator is pretty useful!

Thanks for the links and advice. Greatly appreciated.

Carlos

Hia, Just finished hooking everything up. Ive got a 12V Transformer feeding the mosfet driver board and it's center tapped to give 6V to the 100 Piranah RGB LEDs (resistor values figured out with the LED resistor calculator).

However. When I connect more than one cluster (LED's arranged in groups of 10) the IC2 Transistor's tempriture rockets up. I burned out one board this way as I was loooking at the pretty lights. Luckily I bought two off of you but want to avoid this problem for a second time. Each cluster pulls a combined 0.9A (Red, Blue and Green) So im well under the 15A Limit. And this problem occours when ive only got 4 clusters connected. Ive checked for shorts in my LED arrays and wiring but can find no shorts at all. any idea why this transistor is trying to go nuclear whenever i turn it on?

Thanks. Carlos

You should be using a regulated DC supply to feed the board.

How are you regulating the output from the transformer?

Post a detailed schematic of how you have wired the board up, everything including the transformer, LEDs etc.

Ahhh....Erm...how do you build a regulated DC supply? I kinda figured the part on the board that blew up was the power regulator for the PCB. Basically Ive got a 0-6-12 V center tapped 100VA mains transformer going through a bridge rectifier, then to the PCB. so my two bridge rectifiers and common -V. which come togeather from the PCB. The 12V rectifier goes to V+ on the board. The 6V rectifier goes to the common anode on all the Piranah RGB LED's. The LED's come back to the boards B, G & R Terminals. The red LED's go through 100ohm resistors. And the Green and Blue LED's go through 120ohm resistors.

Sorry for the lack of circuit diagram, tried to use my scanner for the first time in a year and apparently doing nothing has killed it.

Thanks, Chris

Hi Chris

I can’t picture what you have built, partly because even with your description it’s open to interpretation, what I think you’ve done may not be what you’ve actually done. Therefore I can’t help you without a detailed schematic diagram of what you have constructed and preferably some part numbers.

You haven’t mentioned any filter smoothing capacitors on the output of the bridge rectifiers, have you used any?

Have you measured the actual voltage between V+ and GND connection of CN1 on the MOSFET driver PCB and if so what is it?

It’s hard to understand how you have managed to burn out IC2 (which is a voltage regulator, not a transistor) since it has internal thermal overload and output over-current protection. The PCB has a reverse polarity protection diode at the input to IC2 so if you’ve destroyed IC2 you must have got something really wrong. (I suspect it has overheated and shutdown and if you’d left it to cool off it would still work, though what you’ve done to cook it in the first place is still a mystery)

I’d suggest you use Google to do some research on DC power supplies, you’ll find plenty of sites that cover the theory (which you need a bit of) and practical designs. However, if your application needs over 10amps it’s unlikely you’ll find much that you could build yourself so I’d recommend you buy a suitable power supply module.

You wouldn’t normally (okay, I wouldn’t) use a transformer for outputs above 1 amp in this type of application because they are inefficient and since cheap switch mode power supplies are readily available and much better suited to the job it’s easier to just buy one than try and build something.