FETs and gate resistors - scope images

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wight
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comfychair wrote:
[snip]If it’s stable and doesn’t misbehave with just a single cap relocated, does the oscillation on Vcc hurt anything?
Thanks for testing – the results seem reasonable considering the other test results you’ve already shown. I don’t think the oscillation is going to hurt anything. Hopefully others will chime in one way or another. I would still like to move the diode & cap towards VCC, but no sense fooling with that until we’re reasonably sure of things.

I’m a little lost with the most recent trace. I see the spike, but I’m confused about the scales despite your explanation. It seems that the resting voltage of LED- shows up as 2v? And when the FET turns on LED- dips to 0v, and then spikes to >8v when the FET turns off?

I read some about margins recently. Apparently a 20% margin is normal for engineering. As in, if all the parts subjected to the spike can handle an 10v potential from LED- towards B+ (or whatever), then 8v would be OK.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

comfychair
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That's with the probe on LED- & ground clip to battery negative. I only changed the dividers to get rid of the out of range message. The waveform didn't change, just the voltage scale on the side.

By the way, what IS the proper connection to look at the signal to the LEDs?

wight
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Sounds legit to me. Remember I’ve got about the same experience with a scope as you :-). Knowing where that clip goes is just part of keeping us on the same page.

Please try the same test with one probe on LED- and one probe on the FET’s tab (eg the other end of the wire that goes to LED-). I don’t understand well enough to know whether the spike should be worse there or not.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

comfychair
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Well I dunno if this is normal for all oscilloscopes, but on this one grounding the clip on either probe provides ground for both of them. Nothing on screen changes if you have both clipped to ground and then remove either one.

Ground clip to LED-, probe to LED+?

Now that I think about how I had it connected, I think the trace is inverted... it looks almost like a mirror image of the gate signal.

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OK…the BLFDD redesigns are in the works…Mattaus is currently reviewing, finalizing my tweakage of his builds and if they check out he will be re-releasing with the design suggestions you guys recommended

I hope I did him proud!

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Thank you all you guys. I could never have figured any of this out by myself and yet I can follow most of the discussion guing on here. You guys are brilliant! TY Smile

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comfychair wrote:

http://75.65.123.78/scope/V2.jpg

If I want to do this with a zener mod would I replace the diode with the R200 resistor (like normal) and add the zener diode to the now empty C1 pads or does the zener diode have to also have the cap in the factory position?

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

wight
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Cereal_killer wrote:

comfychair wrote:

If I want to do this with a zener mod would I replace the diode with the R200 resistor (like normal) and add the zener diode to the now empty C1 pads or does the zener diode have to also have the cap in the factory position?

We haven’t tested it (AFAIK), but the zener mod drivers simply do not have this problem (we assume). Build them as normal but do not bother with a gate resistor (use a jumper instead).

Specifically:

  • Without the reverse polarity protection diode there is no boost circuit, so the overvoltage condition does not exist
  • Without the reverse polarity diode in place the decoupling cap (C1) should act to smooth out any spikes generated on B+ by the FET switching.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Cereal_killer
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even with the AOD510 I can get away with building them regular and no gate resistor?

thx

edit Sorry I wasnt asking a repetitive question here about the 510’s working in general, I got that, I have one together now on the bench with a 510- I was asking specifically about zener modded old style 17dd’s with the 510…

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

wight
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Cereal_killer wrote:
even with the AOD510 I can get away with building them regular and no gate resistor?

thx

That’s definitely what I’m seeing at this point.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

comfychair
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YES AOD510 WORKS WITH NO GATE RESISTOR* AFTER MOVING C1 TO B+/GND! All of them work with no gate resistor after moving the cap. Even the 15DD with the IRLM2502 works with no gate resistor after moving C1.

*replaced with a jumper on the versions with gate/pulldown pads, pulldown location left open, of course

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I think I have a copy of the BLF15DD, I can re-design it like the BLF17DD is that is what you guys want

In fact, I might be able to make it single sided (nothing on the battery + side of the board)

Working on it now

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I’ve found some strange behavior…

Since getting my 858D station yesterday I’ve built 6 17dd’s (5 this new way and one zener modded), 3 of them with the AOD510’s and 2 with the old Vishay’s are working fine however the one with the one FET I have out of an M6 is giving me some issues with the exact same firmware. It’s heving problems when cycling threw the modes, after turbo sometimes it’ll miss moonlight completely and just go back to low (5-mode off-time with no memory and moon defaulted on without the star needing to be soldered), other times it will go to moon but with a bad preflash.

I’m not really complaining, I have exactly one of these FET’s and dont really mind discarding it to the random parts drawer, just reporting my findings.

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

comfychair
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What's the p/n on the problem FET? Curious to find a datasheet on it and see what it has in the section for gate characteristics. Both the 70N02 & AOD510 have a total gate charge number known to be something the attiny is capable of driving. Above something like Qg=40 they can get troublesome, or at least that's the general number I've heard to stay under.

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DTU
30N02
DD22U

then a little circle symbol with an Lv

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

wight
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Clear PCB images are here that show the FET’s markings and M6 layout: Supfire M6 – resistor mod

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

comfychair
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Wow that thing is awful. Throw it away. Rds(on) is around 0.030 ohms, 70N02 under the same conditions is 0.004-0.006. lol

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This is really great stuff you’ve found out CC and precisely the kind of thing that only comes out after new ideas are tried out and someone takes the time to troubleshoot odd behavior. Good job.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

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wight wrote:
Cereal_killer wrote:

comfychair wrote:

If I want to do this with a zener mod would I replace the diode with the R200 resistor (like normal) and add the zener diode to the now empty C1 pads or does the zener diode have to also have the cap in the factory position?

We haven’t tested it (AFAIK), but the zener mod drivers simply do not have this problem (we assume). Build them as normal but do not bother with a gate resistor (use a jumper instead).

Specifically:

  • Without the reverse polarity protection diode there is no boost circuit, so the overvoltage condition does not exist
  • Without the reverse polarity diode in place the decoupling cap (C1) should act to smooth out any spikes generated on B+ by the FET switching.

So as it turns out the zener modded driver do in fact have the issue, I of course dont have a scope to know if its the very same issue but it was giving me identical behavior where it skipped modes or shut its self down or just overall acted bad when I tried building it with R3 jumpered and C1 populated like normal (with the 10uf cap and the zener diode) and a R200 in place of the protection diode and it did turn on but neither luxdrv fast or phase correct (its known that fet drivers still need luxdrv to run at phase correct PWM) nor my custom weapon mounted UI were usable with it like that. This is in my MT-G2 ZY-T08.
Took it back apart replaced the jumper at R3 with a 130 and populated R4 with a 10k and the light worked perfect with both FW’s!

Brings back the question, can I put the zener diode on the C1 pad with no C1 and put the 10uf cap from batt+ to like with the non-zener ones or does the zener diode REQUIRE the cap to be there?

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

comfychair
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Cereal_killer wrote:
(its known that fet drivers still need luxdrv to run at phase correct PWM)

Most certainly not the case! Only the momentary switch firmwares, that use a different 'sleep' method, require phase correct FW (and that holds true whether it's a FET or 7135s). I built many many lights with FET drivers running luxdrv converted to fast-PWM.

The zener and the cap aren't directly related, they just got piggybacked because they both required connections to the same points. If moving the cap fixes it (which I doubt, since without the normal diode at D1 there is no longer a voltage boosting situation) then that's fine.

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Can I send you the exact .c and hex files I have for luxdrv? When I try changing it to fast and putting it on any of the FET drivers it doesn’t run, or can you send me your file so I can try it?

Fast or slow will work on my 105c (and other 7135 drivers) but this version luxdrv fastPWM doesn’t work on my FET drivers.

Currently the light is running with all resistor pads populated and slowPWM and it didn’t run with R3 jumpered. Ignoring for a second the FW issue fast vs. slow, what should I do with it, leave it as-is or move the cap down to where I am using for 3v ones (your v2 pic) and re-jumper R3?

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

comfychair
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http://75.65.123.78/driverhacks/nanjg-092/ld-fastpwm/

Strobe & ramping deleted, still has memory & battery monitor/beacon mode. Levels are 255, 90, 12, 3.

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@ CC: Your are my hero. And every other modder wanting to be mean to led lights. I never would have thought about getting this heavy into the electronic part of the hobby if it was not for you. TY Smile

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wight
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Cereal_killer wrote:
Can I send you the exact .c and hex files I have for luxdrv? When I try changing it to fast and putting it on any of the FET drivers it doesn’t run, or can you send me your file so I can try it?

Fast or slow will work on my 105c (and other 7135 drivers) but this version luxdrv fastPWM doesn’t work on my FET drivers.

Currently the light is running with all resistor pads populated and slowPWM and it didn’t run with R3 jumpered. Ignoring for a second the FW issue fast vs. slow, what should I do with it, leave it as-is or move the cap down to where I am using for 3v ones (your v2 pic) and re-jumper R3?

Either move the cap or add one where you described.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

seasam
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does anybody happen to have screen shots or images that were posted by comfychair? trying to learn more about the whole C1 cap placement decision on the current iterations of the BLF 17DD.

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seasam wrote:
does anybody happen to have screen shots or images that were posted by comfychair? trying to learn more about the whole C1 cap placement decision on the current iterations of the BLF 17DD.

 

Is this what you are after?

 

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FmC wrote:

seasam wrote:
does anybody happen to have screen shots or images that were posted by comfychair? trying to learn more about the whole C1 cap placement decision on the current iterations of the BLF 17DD.

 

Is this what you are after?

thanks that does help me with the history. I was specifically curious about how noisy the Vcc line gets with the current C1 cap placement since the screenshots are missing. From what I can tell in the comments of this thread there may be noise/spikes with the current C1 cap placement but it was deemed acceptable. Also, I’m still wondering why the gate resistor was deleted if it could have helped with the spikes as well. Guess I need a scope and more studying Party

I’ve been having an issue with a driver built from a wight board running star firmware. When running a triple XPL at high current I’ve been having issues with the driver flickering and shutting down. High current being bypassed springs with LG HE2 cells. Nonbypassed springs or tamer cells don’t seem to have this problem so I was looking here for clues :bigsmile:

I need a scope…

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From memory, the revised C1 placement cleaned up the spike greatly.

That’s interesting, I’m having the same problem with one of the 17mm DD MTN drivers, which is pretty much the same as Wight’s board.

Does your problem driver also switch off if you run it on low for a few seconds?

I know the design of these boards are proven, as there are hundreds of them out there, & I’ve built plenty before this one, but it’s still a pain when you can’t put your finger on a particular issue…

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Weird - I'm using a wight FET+1*7135 driver with the SIR800DP in a triple XPL X6 getting 10 amps with all heavy bypass wires, etc. Basically works well but I got one noticeable issue and it's a blink when changing modes to moon mood, fron turbo or not. RMM recommended trying a resisotr off the FET gate, like a 100K or so -- didn't try that yet.

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FmC wrote:
From memory, the revised C1 placement cleaned up the spike greatly.

That’s interesting, I’m having the same problem with one of the 17mm DD MTN drivers, which is pretty much the same as Wight’s board.

Does your problem driver also switch off if you run it on low for a few seconds?

I know the design of these boards are proven, as there are hundreds of them out there, & I’ve built plenty before this one, but it’s still a pain when you can’t put your finger on a particular issue…

yeah the problem will happen in low it will flicker a bit and then shut off a lot of times. really only in a high current situation though. I can’t remember if it was medium and high too, but definitely low.

my parts are from RMM so I think this driver is a NXP PSMN2R4-30YLDX FET. have some SIR800DP but haven’t tried those yet. I don’t think the FET choice is an issue though.

Tom E wrote:

Weird - I’m using a wight FET+1*7135 driver with the SIR800DP in a triple XPL X6 getting 10 amps with all heavy bypass wires, etc. Basically works well but I got one noticeable issue and it’s a blink when changing modes to moon mood, fron turbo or not. RMM recommended trying a resisotr off the FET gate, like a 100K or so — didn’t try that yet.

funny you should mention the gate resistor because that did seem to be a good thing from this discussion, so I was trying to understand why it was removed from the design in the first place. parts count reasons?

I actually added a 200ohm resistor (replaced the existing diode) and a zener along with a second 10uF cap in parallel with the zenner (also all known as the zener mod – but still running as single cell). C1 still has 10uF cap as well. This was discussed earlier in the thread as a possibility of smoothing out the Vcc line.

To be honest I haven’t been able to get my light to act up again after doing the zener mod with this single cell driver. It was pretty easy to reproduce the behavior before I added the zener. I would like to try the gate resistor at some point too (without the zener). I will probably build another driver and keep tinkering. I’ll update if my driver acts up again.

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