I think your pictures or attachments are being blocked by the Mods until your post count is a little bit. I'd love to be able to help you, but without being able to see what you're doing, it's impossible right now.
DIY LED driver for reef lighting
- Thread starter der_wille_zur_macht
- Start date
I think your pictures or attachments are being blocked by the Mods until your post count is a little bit. I'd love to be able to help you, but without being able to see what you're doing, it's impossible right now.
Hi guys,
I am working on a project, using the LM3409 buck converter. I saw that you had some interesting discussions going on about that chip, and I wondered if you could have a look at my problem?
The constraints are:
Vin 12 - 40V, Vout: 9V, Iout: 1-5A, frequency: approx. 500kHz.
Shunt: 47m Ohms
Coff: 2nF, Roff: 220 - 10k Ohms.
I simulated the project, and everything was fine.
When I built it, I saw that there are several very short on- and off- switching states within one free-wheeling cycle. The time between them is approximately the off-time.
Now I red the datasheet, and that says, that the LM3405 switches the + and - comparator inputs with every cycle - leading to an offset of 24mV.
-> the current has to decrease by more than 0.5A before the next switching cycle - if a shunt of 47m Ohms is used.
This is a problem, because it leads to a very high inductor current ripple and to many switching cycles, which leads to a thermal problem of the switch.
If the current is reduced, or the off-time is reduced, the switching cycles within one free-wheeling period become less.
Does someone have an idea where this problem might come from and what could be done about it?
Did anyone have a similar problem?
Thanks,
Philipp
I am working on a project, using the LM3409 buck converter. I saw that you had some interesting discussions going on about that chip, and I wondered if you could have a look at my problem?
The constraints are:
Vin 12 - 40V, Vout: 9V, Iout: 1-5A, frequency: approx. 500kHz.
Shunt: 47m Ohms
Coff: 2nF, Roff: 220 - 10k Ohms.
I simulated the project, and everything was fine.
When I built it, I saw that there are several very short on- and off- switching states within one free-wheeling cycle. The time between them is approximately the off-time.
Now I red the datasheet, and that says, that the LM3405 switches the + and - comparator inputs with every cycle - leading to an offset of 24mV.
-> the current has to decrease by more than 0.5A before the next switching cycle - if a shunt of 47m Ohms is used.
This is a problem, because it leads to a very high inductor current ripple and to many switching cycles, which leads to a thermal problem of the switch.
If the current is reduced, or the off-time is reduced, the switching cycles within one free-wheeling period become less.
Does someone have an idea where this problem might come from and what could be done about it?
Did anyone have a similar problem?
Thanks,
Philipp
common ground?
common ground?
Hi,
I'm using the CAt4101 board with an arduino.
My LED strings don't turn on. I think the issue might be the ground but I'm just not sure how to wire it to the arduino and the power supply.
I have a 24v 5A power supply with 100-240v input. It has V- V- V+ V+, do I connect the ground pin on the arduino to the V- on the power supply?
I fried an arduino by connecting the digital ground to V- (I wasn't paying attention)...
Thanks
common ground?
Hi,
I'm using the CAt4101 board with an arduino.
My LED strings don't turn on. I think the issue might be the ground but I'm just not sure how to wire it to the arduino and the power supply.
I have a 24v 5A power supply with 100-240v input. It has V- V- V+ V+, do I connect the ground pin on the arduino to the V- on the power supply?
I fried an arduino by connecting the digital ground to V- (I wasn't paying attention)...
Thanks
Yes- Make sure that your CAT4101 board & the Arduino's ground pin all connect back to the V- terminal of your power supply.
Not bright eh? Have you verified how much current they're being driven at? Maybe it's less than you assume?
The diodes were sold to me as XPE2. The spec says they should have a forward voltage of 3.15 @ 1000 mA. I have 7 in a string and the drop is 15.3v. The actual part they told me it was is XPEBWT-L1-0000-00BE7.
They came on a star pcb but the print doesn't look legit... What do you think?
I bought the CAT4101 back when I had a reef but moved across provinces and left all the hardware sitting in a box for 3 years. I recently decided to try it out just for fun. That's why the lights are white, I don't really have a use for the other colors right now.
They came on a star pcb but the print doesn't look legit... What do you think?
I bought the CAT4101 back when I had a reef but moved across provinces and left all the hardware sitting in a box for 3 years. I recently decided to try it out just for fun. That's why the lights are white, I don't really have a use for the other colors right now.
As O2Srplus said, test the current. If they are being driven on a low current, you'd see a lower voltage across them and less light.
Cree only supply the actual emitter - the star is usually supplied by whoever reflows the emitter on to it, so the lettering could be done by anyone and still a genuine cree LED.
Tim
Cree only supply the actual emitter - the star is usually supplied by whoever reflows the emitter on to it, so the lettering could be done by anyone and still a genuine cree LED.
Tim
Hi Tim,
How do I test the current?
I've set the power supply to 24v using the trim pot on it. The PWM on the CAT4101 is connected to 5v. If I recall correctly, the CAT4101 board as designed here, is 700mA so the voltage drop on the xpe2 should be 3.05.
Now 15.3 / 7 = 2.19 so I'm pretty far from what I should see right?
How do I test the current?
I've set the power supply to 24v using the trim pot on it. The PWM on the CAT4101 is connected to 5v. If I recall correctly, the CAT4101 board as designed here, is 700mA so the voltage drop on the xpe2 should be 3.05.
Now 15.3 / 7 = 2.19 so I'm pretty far from what I should see right?
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Using a multimeter on the ammeter setting. It needs to be part of the circuit (ie the +ve supply goes the the ammeter and then the ammeter connects to the +ve in on your LEDs).
Or, just drop a 9V battery across three of them and see if they look brighter then when normslly powered up. A 3V source across one is easier, if you have one...
2.19 is about riht for XPE at 700mA. For XPE2, it would be more like 10mA!!!!
Tim
Another simple method to use if your meter can't handle amps (some only measure mA) you would need a meter with a 10amp setting(usually a separate plug for the positive lead.
you can use a resistor wired in series with the string. a 1ohm resistor works fine for this you will want at least a 1 or two watt resistor so it doesn't burn up during the test. you then set the meter to measure milivolts or volts and measure across the two ends of the resistor. using a 1ohm resistor the voltage reading equals the current. I.E. 700mA current would give a voltage of either 0.7volts or 700mV depending on the setting on your meter.
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