Desperatly looking for driver (updated kennan driver?)

[jtr1962]

Glad to be of help! Enjoy the drivers!

 

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Received my two drivers from Kaidomain yesterday, 8th of March. Ordered 12th of January. They have the same pcb's as MikePL, but they have all components except for R6 connected. Will post pictures later. Havn't tried them yet.

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[TorchBoy]

Re: Desperately looking for driver (updated Kennan driver?)

See page 5 of the datasheet for some typical dimming methods. ... all of these methods may be employed.

So the extra IC would be for PWM dimming?

Why do some of these photos have a 22µH inductor and some a 47µH one? (I think those units are right.) I noticed that for the first version too. What difference does more than doubling the value of the inductor make?

 

[jtr1962]

Re: Desperately looking for driver (updated Kennan driver?)

So the extra IC would be for PWM dimming?

Why do some of these photos have a 22µH inductor and some a 47µH one? (I think those units are right.) I noticed that for the first version too. What difference does more than doubling the value of the inductor make?

Increasing the inductor value just smooths the current to the LED a bit more, that's all. The new version uses a smaller value inductor but has a ceramic cap in parallel with the LED. The capacitor also smooths the current.

Regarding PWM, not sure what extra IC you're referring to here. Can you be more specific? In all the photos I see there's just the PT4105 driver IC. All the rest of the parts are either resistors, inductors, capacitors, or diodes.

 

[TorchBoy]

Re: Desperately looking for driver (updated Kennan driver?)

The new version uses a smaller value inductor ...

Does it? This pic shows it marked 470, and has the board fully populated except for R6.

Regarding PWM, not sure what extra IC you're referring to here. Can you be more specific? In all the photos I see there's just the PT4105 driver IC. All the rest of the parts are either resistors, inductors, capacitors, or diodes.

Have you noticed that all the photos on the product page are new? In the first photo (link above) it's called IC1 and marked as 82FE.

 

[jtr1962]

Re: Desperately looking for driver (updated Kennan driver?)

Does it? This pic shows it marked 470, and has the board fully populated except for R6.


Have you noticed that all the photos on the product page are new? In the first photo (link above) it's called IC1 and marked as 82FE.

Sorry, I didn't even look at the product page until now, so I really had no idea what you were referring to. Electronically, there's not much difference between a 22µH and a 47µH inductor. It was probably a matter of one part being cheaper or more available than the other. IC1 is probably a voltage regulator but it could also be a transistor or a diode mislabeled as an IC. It does indeed look like it has something to do with PWM. If I had to guess, I'd say it's a transistor which pulls the FB pin high in order to turn the LED off via a PWM signal.

 

[MikePL]

Re: Desperately looking for driver (updated Kennan driver?)

Hmm... I wonder what those extra components add to the driver? All the drivers I have are just like the one in the photo on top of the page. No IC1 no resistors... but I have the R6

 

[TorchBoy]

Re: Desperately looking for driver (updated Kennan driver?)

IC1 is probably a voltage regulator but it could also be a transistor or a diode mislabeled as an IC. It does indeed look like it has something to do with PWM. If I had to guess, I'd say it's a transistor which pulls the FB pin high in order to turn the LED off via a PWM signal.

Sounds good. 3 pins, so I wouldn't think diode.

Hmm... I wonder what those extra components add to the driver? All the drivers I have are just like the one in the photo on top of the page. No IC1 no resistors... but I have the R6

And it's just a link. :thinking: Apparently a board tuneable for multiple applications. We could do with some sort of application notes for this particular board.

If the set resistor is 0.2 ohms, is the output now 1A instead of the old 750mA?

 

[mike2g]

I'm sorry but the workings of this board is beyond me. Does anyone know what resistor could be used to replace the supplied 0.2ohm one that would produce 350mA?

 

[TorchBoy]

The datasheet says a 0.57 ohm resistor will give a fixed 350mA output. (I haven't received the new version of the board yet, so I haven't seen if there's an easier way provided by all the new resistors etc.)

 

[[email protected]]

I got some of the new Kennans with IC1, R4, and R5, but no R6. The extra parts make the driver shut down for input voltages below 6.2 volts. My guess is these parts are designed to shut down the driver when 2 Li-Ion cells driving it get below their safe operating voltage.

It seems you can pretty easily bypass this "feature" by shorting out R4. Or else by removing IC1, R4, R5 and then installing a piece of wire for R6. I'm a little bummed to have to be doing this on the drivers I got. I really like being able to drive a LED off of 4 NiMh batteries, and with IC1 installed, that's not gonna happen.

Mark

 

[TorchBoy]

Or else by removing IC1, R4, R5 and then installing a piece of wire for R6.

Sounds like what the initial run of this new version had, as per the pic posted by MikePL.

Nice deductive work, BTW.

 

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I've tried to make a schematic of the boards I received and taken a few pictures. One of my boards has a 22uH and the other a 47uH inductor. They also have different R2, one 5k1 the other 3k.

As far as I can read from the datasheet (PT4105), the CE-pin (chip enable) needs at least 1.5V to "start" the chip. When going below 0.3V it will shut down again. I agree with Mark that the R4+5+7 and IC1 have the task of regulating the voltage to the CE-pin and thereby enabling / disabling the PT4105 at certain supply voltages. By changing/adjusting these resistors one probably could change shutdown voltage to what ever one like.

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[nein166]

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Awesome Picture!
Oh and thanks for the the schematic. Changing the shutdown voltage would save my cells when running on multiple Li-Ions.

 

[TorchBoy]

So are these in stock or aren't they? Has anyone had any shipped since the web site started claiming they are in stock again?

 

[[email protected]]

So I finally tried removing IC1, R7 and R5 (if you pull off IC1 and R5 you don't need to bother with R4), then I shorted out R6. Everything seems to work fine.

But I noticed something different. With R1 set at .200 ohms, the driver drives the LED with about 1 amp of current. So the LED runs a lot brighter than previous versions of the driver (the old version of the driver ran at around .8 amps I think).

The LED now runs a bit hotter, which I would expect. And the driver chip now gets pretty warm, like too hot to touch after a few minutes. I looked up absolute max current for the driver chip and it's listed as 1.5 amps. But the recommended operating current is less than .7 amps.

Anybody try running one of these for a long time? My tests have all been pretty short, less than an hour. I'm wondering if these drivers are going to be more failure prone due to the higher current.

Mark

 

[TorchBoy]

Re: Desperately looking for driver (updated Kennan driver?)

If the set resistor is 0.2 ohms, is the output now 1A instead of the old 750mA?

But I noticed something different. With R1 set at .200 ohms, the driver drives the LED with about 1 amp of current. So the LED runs a lot brighter than previous versions of the driver (the old version of the driver ran at around .8 amps I think).

Thank you for that confirmation. The datasheet indicates it shouldn't be run at 1A with less than 9V in, so I'm a little surprised at that change.

 

[MikePL]

Re: Desperately looking for driver (updated Kennan driver?)

I have one more question about this driver. Can it be powered without the LED connected on the other end? I heard that some drivers need an output in order not to burn. I am about to make a light and I would like to have a switch which would either power one LED or three. While switching there is always a 'gap' which lasts 0.2s and I would like to know it such a repeated switching can damage it.

 

[jtr1962]

Re: Desperately looking for driver (updated Kennan driver?)

I have one more question about this driver. Can it be powered without the LED connected on the other end? I heard that some drivers need an output in order not to burn. I am about to make a light and I would like to have a switch which would either power one LED or three. While switching there is always a 'gap' which lasts 0.2s and I would like to know it such a repeated switching can damage it.

In general, step-up drivers are the ones in danger of burning out if no load is connected. What happens is that the output voltage increases without limits until it exceeds the ratings of the pass element or the output capacitor. Once that happens, you get catastrophic failure (in layman's terms lots of smelly smoke). Some step-up drivers have output voltage limits to prevent this from happening.

Since this isn't a step-up driver, but rather a step-down one, this failure mode can't happen. With nothing connected the pass MOSFET will simply be driven at maximum duty cycle, and the output voltage will be a little less than the input voltage. This can't harm anything.

 

[TorchBoy]

Re: Desperately looking for driver (updated Kennan driver?)

Some step-up drivers have output voltage limits to prevent this from happening.

Would a zener diode do that job? :thinking: