BLF17DD Info Thread - Reference

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RMM
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Yep.  That works.  You can use a very small PFET, just use one that has sufficient voltage ratings.  You may also need a pull up resistor to keep it off, but you'll have to figure that out in use.  

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FmC
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Is there a reason I can't use the  LFPAK56 or DPAK-2 in lieu of the PFET in that diagram?

Or even a 7135 ?

Thanks.

 

 

 

 

RMM
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Do you understand the difference between a P channel and N channel FET?  

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FmC
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RMM wrote:

Do you understand the difference between a P channel and N channel FET?  

FmC wrote:

I can see this quickly getting over my head.....

I tried reading up on them, but I'll just accept a "no", & move on to locating a suitable P channel.

All I know is that the FET doing the main switching is rather loaded with a lot of current, so the AtTiny is having dramas moving the switch(NFET), so we are using an intermittent switch (PFET) to lend a hand.  

I know that's probably the least technical description, & will make someone who knows what they are talking about cringe....  Wink

-- edit --

I now understand enough to see why the N channel would not work.... from a Positive feed.

FmC
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Will this one do the trick?

Transistor Polarity: P Channel
Continuous Drain Current Id: 11A
Drain Source Voltage Vds: 200V
On Resistance Rds(on): 500mohm
Rds(on) Test Voltage Vgs: -10V
Threshold Voltage Vgs Typ: -4V
 Power Dissipation Pd: 125W
 Package: TO-220
Pulse Current Idm: 44A

Full Datasheet.

RMM
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I'd get one with a much lower voltage rating (you'll get better overall specification for your application).   I'd look at an SOT-23 package.  That 44nC gate charge is really high and you don't need a huge TO-220 package.  

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FmC
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Thanks for pointing me in the right direction.

I've got some of these on the way.

RMM
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Those ought to work well. Cool

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Kloepper Knife Works
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I’ve been hitting a wall. I’m putting together an Triple XP-L for woodfiend, and I have a problem. When I put it together (assemble the light, with driver soldered to the pill) the light loses its ability to change modes. I didn’t notice until I went to do measurements on it, and I’m wondering if it’s not the driver but the LED’s(but I can’t fathom why).

I’m using BLF17DD’s (I’m on the second one, I assumed the first one was bad, but the second is doing the same thing). When I tested it on my PSU before soldering the driver everything worked. Soldered the driver in place, still working. Assemble the light, mode switches 1 time only then not any more. I can program the guppydrv and set mode groups and it will start at whatever the modes first level is, but won’t change.

Do I just need to bite the bullet and start replacing LED’s?

Werner
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Have you tried longer and shorter switching off and on? Maybe you have a problem with the off time memory capacitor?

RMM
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It is bizarre that it will go into programming mode but not change modes.  What BLF17DD revision are you using?  V1.0?

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Kloepper Knife Works
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Werner wrote:
Have you tried longer and shorter switching off and on? Maybe you have a problem with the off time memory capacitor?

Yes I have. I had the same concerns about the OTC, but considered it unlikely when a second driver with all new components exhibited the same issue once assembled into the light. Not saying it’s completely ruled out, but I’m doubtful at this point that it’s the culprit.

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RMM wrote:

It is bizarre that it will go into programming mode but not change modes.  What BLF17DD revision are you using?  V1.0?

They’re actually MTN17DD’s, I remembered wrong. Version 1.11, you’re special batch of boards with the masked + pad. Using the guppydrv firmware you flashed for me.

This is the 8th or 9th I’ve assembled, and only 1 other had any issues after assembly(I think that one got overheated).

RMM
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Can you try it with a half-full or weaker battery?  The voltage may be boosting too high for the MCU which causes it to glitch.  I've seen this happen on really heavy loads with full high-drain cells on some drivers.  

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ToyKeeper
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RMM wrote:
It is bizarre that it will go into programming mode but not change modes.

That is definitely weird. I wonder if it uses on-time (exclusively) to determine whether to enter programming mode, and off-time (exclusively) for changing modes. That way, an issue with the OTC draining too fast could result in the symptoms described.

Maybe the OTC got shorted so it can’t hold a charge?

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OK, so a weaker cell doesn’t appear to make a difference. But now it won’t go into programming mode. Grrrrr. I know for sure that the lead wires are not shorting out, and the jumpers are on for parallel operation. The driver isn’t bottoming out in the pill, and it was the best reflow job I’ve done yet.

D o e s n ‘ t m a k e s e n s e.

Tom E
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I try to always test in phases, sounds like you did the same thing, I'm just not clear - what was the last configuration that the driver worked properly in switching modes? I know you said soldered the driver in and it worked, but was the LED's all soldered in place? Is it a removable pill assembly? I pretty much always test with a real cell on the pill assembly, then after installing the pill, test with a cell again. The PS is great for doing a first trial at low power, but after that, I'll still test with a cell.

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I find it really helpful to have a couple alligator clips which lead to wire with exposed ends, so I can clip one to the ground ring and one to the spring and then hold the wires onto a battery for testing. Or hold them onto the battery and tap the clip against the body to test after putting the pill in. Or a variety of other methods, testing at each step like Tom E suggested. It really helps with determining what failed.

I’ve had some which fail after putting the reflector in, which is fixed by putting kapton tape on the back of the reflector. Yesterday I had one where the front half of the light worked but it failed after attaching the back. It turns out that one was a bad switch.

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Tom E wrote:

I try to always test in phases, sounds like you did the same thing, I’m just not clear – what was the last configuration that the driver worked properly in switching modes? I know you said soldered the driver in and it worked, but was the LED’s all soldered in place? Is it a removable pill assembly? I pretty much always test with a real cell on the pill assembly, then after installing the pill, test with a cell again. The PS is great for doing a first trial at low power, but after that, I’ll still test with a cell.

Last working configuration was with LED’s soldered to MCPCB, MCPCB soldered directly to the pill, lead wires soldered to MCPCB and driver, driver soldered into pill. But I didn’t test “extensively” after soldering the driver in place before assembling, so if it’s something that takes a bit of time to become damaged it’s possible it just hadn’t happened yet, but could have if I tested longer before assembly. My gut is telling me that something bad is happening in assembly when the carclo optic seats. The only reason I’m not more confident is that all 3 LED’s light and appear equally bright.

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Could check the LED wires for signs of cuts at the openings - it's happened to me before. The silicone wires will get cuts thru the insulation pretty easy, and results can be intermittent, frustrating... Dunno - that might be a long shot. Hard to imagine scenarios where the Carlco lens might be causing a short. With the MCPCB soldered down, no chance of twisting. Could be some short relating to something on the edge, against the host body, again, long shot. Weird it happened with two drivers...

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Tom E wrote:

Could check the LED wires for signs of cuts at the openings – it’s happened to me before. The silicone wires will get cuts thru the insulation pretty easy, and results can be intermittent, frustrating… Dunno – that might be a long shot. Hard to imagine scenarios where the Carlco lens might be causing a short. With the MCPCB soldered down, no chance of twisting. Could be some short relating to something on the edge, against the host body, again, long shot. Weird it happened with two drivers…

I actually trimmed them back when I reassembled with the second driver to make sure this wasn’t happening. When my son goes down for a nap this afternoon I think I’m going to replace all 3 LED’s and see if the second driver starts working(assuming it checks out ok after I remove it from the pill, if not I’ll try another one). If not I’ll be starting completely over with a new MCPCB, LED’s, wires, and driver all at the same time.

Not going to make anything on this build. Oh well, the risk of living on the edge.

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That really is frustrating.  I feel your pain.  I've been doing this for a while and I still get crap like this that I can't figure out.  I think that it happens to all of us, even if we don't post about it all the time! 

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Fritz t. Cat
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Is the off time capacitor touching anything?
Is the switch too noisy?

Flashlight designers should look at lighthouses and pottery.
这些谁设计的手电筒应该看灯塔,以及在陶器。

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RMM wrote:

Yep.  That works.  You can use a very small PFET, just use one that has sufficient voltage ratings.  You may also need a pull up resistor to keep it off, but you'll have to figure that out in use.  

 

I think I'll be able to use one of the old BLF DD two sided driver boards for this project, to keep things fairly neat.

This is what I have in mind;

 

Note, the PFet is upside down, to get the legs where I want them.

If I were to require a pull up resistor, what value would be a good starting point?

 

Fritz t. Cat
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You have a short in that diagram. It will have the sort of problem that makes the bad smell. Evil

Flashlight designers should look at lighthouses and pottery.
这些谁设计的手电筒应该看灯塔,以及在陶器。

FmC
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Fritz t. Cat wrote:
You have a short in that diagram. It will have the sort of problem that makes the bad smell. :evil:

Hmmm - Richard seems to think that circuit would work (Look back to post#268 in this thread where we were talking about it).

 The XHP's from MTN should arrive any day now, & I'm at the stage where I need to put a driver together to get things happening with the build.

Can you elaborate on why the magic smoke will escape? Smile

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Sorry. I wasn’t noticing C1.

Flashlight designers should look at lighthouses and pottery.
这些谁设计的手电筒应该看灯塔,以及在陶器。

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RMM wrote:

I think you could get away with a single FET for that build with a little creativity: use a small PFET to power the NFET gate directly from the 8V+ input.  It will load the attiny way less and will give the FET access to higher gate voltages, which will decrease the resistance of the FET.  You could also easily power more than one FET off the same attiny, if needed.  You would need to basically invert the PWM values, since the PFET turns on when the gate is pulled low.  

It is a crazy untested idea, but in theory it should work.  I don't think you need a dedicated gate driver IC since we're switching relatively slow. 

Richard,

I've built the driver today, but I'm having trouble getting modes to work. It's stuck on full output.

I have tried pull-up resistors from 10k - 220k between the Source & Gate of the P Fet.

I also tried a 100 ohm pull down resistor on the big N Fet, between Gate & Ground.

 

I'm wondering if I have something wrong in the firmware;

When you say to invert the PWM values, do you just mean that Highest mode is "0" & Lowest (off) is "255" , or is there something else I need to change in the firmware as well?

 

Cheers.

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If I understand correctly, PWM=0 would be the highest mode, and PWM=255 would be off. Anything between would be, well, between.

If it’s stuck on maximum, is there a short somewhere?

Or perhaps is it always resetting to the first mode, unable to sense how long it was off? You might want to try an on-time based firmware to rule out that possibility.

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I removed the P Fet (taking the driver back to a regular Zener-modded driver)to check operation, & it tested OK with mode levels(albeit reversed, now).

...But on further reading, I think what Richard is saying, is that the actual signal from the Attiny needs to be inverted.

I came across this info, but I'm not sure how/where to add it into the firmware.

Specifically, the following is what I believe needs to be changed;

 

---------------------

COM – Compare Output Mode

 

These bits are used to set the Output mode in various Wave form generation mode. For Fast PWM mode these can be used to achieve following output modes.

 

COM01
COM00
Output Mode
0
0
Normal Port Operation (OC0 disconnected)
1
0
RESERVED
0
1
Non Inverted PWM
1
1
Inverted PWM

-----------------

So I need to put a command in there to set COM01 & COM00 to 1,1.

...I think... :~

 

- edit -

The info I linked above appears to relate to the ATmega16 or ATmega32, but I basically need to do the equivalent to the 13a.

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