Kaidomain 8X7135 wiring

[tome9999]

I bought a couple of the Kaidomain 8X7135 drivers (http://www.kaidomain.com/ProductDetails.aspx?ProductId=1770) to use in a Mag3D with a P7 and LSD NiMH batteries. They didn't come with any documentation of any sort and in fact look different to the ones on the web page.

Does anyone know how I wire them? Attached are a couple (cell phone) pics.

Tome9999

 

[Benson]

Looks like:

• red wire = v+ (battery+ and LED+ for typical applications...)
• black wire = LED-
• peripheral ring = battery-

Interesting to see that their silkscreen still shows D1 and D2 labels same as old style with 2 diodes...

 

[ti-force]

+1

l can draw a diagram for you if you need it. Also, if this were my project, I'd remove both of the diodes and bridge the connection.

 

[tome9999]

+1

l can draw a diagram for you if you need it. Also, if this were my project, I'd remove both of the diodes and bridge the connection.

If Benson is correct (thxs Benson) then I don't think I need a diagram.

What does removing/bridging the diodes do for me?

Thanks
-Tom

 

[Benson]

The diodes are to prevent blowing out the AMC7135s with reverse voltage should you drop batteries in backwards. In theory, I suppose they also stretch the maximum input voltage up a bit to 6.6V, but AMC7135s become inefficient and hot when driving typical white LEDs above 5V input anyway.

Removing them allows the driver to function at somewhat lower voltages, but doesn't really matter with white LEDs because you'll already be out of regulation before that's an issue. Since the AMC7135 is specced to work at 2.7V, 0.6V for the diode means it should work down to 3.3V, at which point the LED is seeing about 3.15V.

If you wanted to build, say, a red LED (Vf around 2.5V) from 2 alkaline, 1 3V Li, or 1 LiFePO4, this would be necessary. Or if you think you got really lucky with Vf and won't have dropped out to useless levels at 3.15V.

 

[ti-force]

If Benson is correct (thxs Benson) then I don't think I need a diagram.

What does removing/bridging the diodes do for me?

Thanks
-Tom

The diodes reduce voltage, so I remove them. When removed, the circuit is broken (the diode no longer makes the circuit), so you need to re-make the connection. Like this:

 

[kramer5150]

I always wire jump the diodes on my 7135 boards, provided you can solder it cleanly, it eliminates the Vdrop through the diode.

Note this is a 1.4A board, not a sandwich'd pair.

 

[tome9999]

I haven't removed the diodes yet, but will. However, it seems to be supplying only a fraction of the current that it should.

I have it wired as you suggest, I put 3 NiMH D batteries (which read 3.9VDC) in series with my ammeter. It lights but is only drawing about 800mA. What could be the problem?

Tome9999

 

[tome9999]

Hmm, when I direct drive the LED from the batteries with the ammeter inline I also get only 800mA...?

 

[tome9999]

Must be a problem with my Beckman meter, when I direct drive without the meter, though I can't tell how much current is being drawn, it is blinding.

 

[Justin Case]

The Vf of your P7 may be sufficiently high that when you insert your meter in the circuit, the resulting extra resistance (and thus voltage drop) is enough to knock the AMC7135 driver way out of regulation. Between the possibly high LED Vf, the relatively low Vbatt, and the reverse polarity diodes that are still installed, you may not have a lot of voltage headroom to work with.

I would definitely remove the diodes.

What Vf bin code did you get for your P7?

 

[tome9999]

The Vf of your P7 may be sufficiently high that when you insert your meter in the circuit, the resulting extra resistance (and thus voltage drop) is enough to knock the AMC7135 driver way out of regulation. Between the possibly high LED Vf, the relatively low Vbatt, and the reverse polarity diodes that are still installed, you may not have a lot of voltage headroom to work with.

I would definitely remove the diodes..

Got it.

What Vf bin code did you get for your P7?

They were DSWOJ. Since my driver board looks different then yours, I assume that I should remove only the one diode (on each side) and bridge that gap ONLY? That is, I shouldn't bridge all the way across like yours should I? I would just be shorting the red and black wires if I do that.

Tome9999

 

[Justin Case]

Examine your board closely. You can see where the traces connect the diodes to one leg (Vdd) of the AMC chips, whereas the black wire connects to a different leg (OUT). Based on that observation, what would you conclude about the wisdom of making a "bridge all the way across", resulting in a short between the Vdd and OUTlegs of the AMC chips?

J Vf bin is the wrong one to use for an AMC driver and 3xNiMH. You should have gotten I Vf bin.

Power up your P7 again with your AMC driver and freshly charged 3xD NiMH cells. It should be running in full regulation under those conditions. at least initially. Measure the LED's Vf. Hopefully, it is around 3.5V or less, though I'm tending to doubt that will be the case. If it is ~3.7V or more, I think you need to re-assess your build. That magnitude of Vf IMO is too high for an AMC driver powered by 3xNiMH. Either get a lower Vf P7, or use a 4D host.

 

[tome9999]

J Vf bin is the wrong one to use for an AMC driver and 3xNiMH. You should have gotten I Vf bin.

Power up your P7 again with your AMC driver and freshly charged 3xD NiMH cells. It should be running in full regulation under those conditions. at least initially. Measure the LED's Vf. Hopefully, it is around 3.5V or less, though I'm tending to doubt that will be the case. If it is ~3.7V or more, I think you need to re-assess your build. That magnitude of Vf IMO is too high for an AMC driver powered by 3xNiMH. Either get a lower Vf P7, or use a 4D host.

It measures 3.3V with the LED powered up. Seems well within spec.

Tome9999

 

[Justin Case]

Looks like you are in business. Folks like jtr1962 have commented that Vf bins are not always accurate (among other issues with guessing an emitter's Vf), but I suggested I bin vs J bin since that's a buyer's only tangible guideline short of the seller hand-selecting an LED.

It also looks like your meter adds a lot of voltage drop to be able to take your light out of regulation with such a low Vf.

 

[tome9999]

It also looks like your meter adds a lot of voltage drop to be able to take your light out of regulation with such a low Vf.

Not sure what you mean by the meter adding voltage drop to take the light out of regulation... How is it taking it out of regulation? Are you talking about my earlier current measurements? BTW, to measure Vf I was using a different meter (Fluke 322) vs the Beckman I was using for current measurement...

BTW, thanks for the help!

 

[ti-force]

Not sure what you mean by the meter adding voltage drop to take the light out of regulation... How is it taking it out of regulation? Are you talking about my earlier current measurements? BTW, to measure Vf I was using a different meter (Fluke 322) vs the Beckman I was using for current measurement...

BTW, thanks for the help!

I'm not trying to answer for Justin Case; he knows more about this stuff than I'll probably ever know, but he means the resistance of the meter is causing you to have voltage drop.

 

[ti-force]

The Vf of your P7 may be sufficiently high that when you insert your meter in the circuit, the resulting extra resistance (and thus voltage drop) is enough to knock the AMC7135 driver way out of regulation. Between the possibly high LED Vf, the relatively low Vbatt, and the reverse polarity diodes that are still installed, you may not have a lot of voltage headroom to work with.

I would definitely remove the diodes.

What Vf bin code did you get for your P7?