D.I.Y. Illuminated Tailcap - gChart Editions

153 posts / 0 new
Last post
gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

I’ve tried 680 and 300 ohm bleeders so far, didn’t make any difference. I haven’t tried different tailcap resistors. I’m not against that, but hopefully this will be flexible enough where that wouldn’t matter much.

Schoki
Schoki's picture
Offline
Last seen: 2 weeks 18 hours ago
Joined: 03/27/2017 - 15:34
Posts: 218
Location: Germany

First, I want to say that the voltage regulator on the tail capis a really good idea. I hope we all can see more little projects like this. And you made a very good video! Explains all the little details (especially the dimming on the LiIon cell).

Now I will make a really technical theory that could explain the problem. But don’t think that if it’s me pointing out a problem, that it’s 100% correct. I could be wrong as well, i’m just guessing here:
It’s clear that there is current flowing from the boost circuit input to ground. And when you go higher in current, it starts working. There’s enough current flowing through the TPS61221 for the low modes, but not for the higher ones.
The only pin possible is the L pin.
When you have your light off, and screw the tail on, the tail starts lighting up. Then you click, and the main LED goes on, the tail goes off (all normal behaviour). Now if you then click, the main LED won’t go off. I think this has to do with the way the IC controls the boost operation. The TPS61221 has a so called “hysteretic current mode” control circuit (variable frequency control). It keeps the current ripple on the inductor at 200mA, and offsets the current ripple according to the load. This way the voltage stays constant. Now that’s a problem in your situation. It simply won’t reach the 200mA to start switching when you click in the low mode. This is why the lamp stays on. The IC tries to charge the inductor until the current reaches 200mA (by turing on the lower MOSFET from the inductor to ground —> current flow keeping the LED on), but it never reaches 200mA. The current keeps flowing and the main LED stays on.
On the higher modes it works, not sure why though. That’s why I’m not sure. It should be the same result all the time with my theory.
I don’t understand the exact coherence (is that the right word to use here?) of the mode switching and the 200mA hysteresis right now, but I think this is the reason.

I’ll try to completely understand though.

Schoki
Schoki's picture
Offline
Last seen: 2 weeks 18 hours ago
Joined: 03/27/2017 - 15:34
Posts: 218
Location: Germany

To be honest, I’m impressed the boost circuit works in the first place, it should never reach 200mA ripple because of the bleeder. On startup, the boost IC isn’t controlled with the hysteresis, but with a special startup controller with limited switching current (look at Figure 20 in the datasheet)

CRX
CRX's picture
Offline
Last seen: 1 hour 23 min ago
Joined: 04/02/2013 - 15:27
Posts: 4037
Location: Scotland

Nice work Thumbs Up

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Does the input capacitor help in it attaining startup? In my testing, I tried removing the input capacitor. No real change on Li-Ion. On NiMH it failed to startup in any mode… wouldn’t work at all.

What if a different IC was identified that had a lower ripple current? That’s the same as “switching current”, right? It looks like the Ricoh R1210N331D-TR-FE (3.3V version) has a 100mA switching current rating.

Schoki
Schoki's picture
Offline
Last seen: 2 weeks 18 hours ago
Joined: 03/27/2017 - 15:34
Posts: 218
Location: Germany

Ripple current is the difference between the highest current and the lowest current flowing through the coil (the delta current).
switching current is either the average current, or the absolute maximum current flowing through the inductor, depending on the subject you’re talking about (from x axis to the average, or the highest point)

The Ricoh could work, but I would keep looking for some alternatives, I’m sure there are better options. Does it have to be a package with leads, or is a no-lead package okay as well?

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Thanks for the explanation. I’m good with a no-lead package as I’ll be hot-plate reflowing them. I’m definitely open to suggestions if you care to join the search!

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Another thought… If I could get the input capacitor to hold it’s charge when the flashlight is turned on, perhaps it could be used to handle the ripple during startup as the flashlight is switched off? If hooked up correctly, placing a transistor between the input cap and VIN could do this, right?

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Another theory… some (most?) of these chips will pass current through the chip if the Chip Enable pin hasn’t reached the turn-on voltage (0.5V?). The TPS61221 is this way (“Pass-Through Function during Shutdown”). Perhaps on the flashlight’s low mode, the voltage reaching the PMIC is low enough that it’s not tripping Chip Enable and is instead just passing current through the IC.

Some PMIC’s have a “Load Disconnect” feature that essentially disconnects the IC if the Chip Enable is too low. Maybe that would force the main driver to shut down, giving the tailcap an opportunity to start up? I see TPS61261 has Load Disconnect (also something called “soft start” that may be helpful?), but unfortunately it’s only rated up to 4.0V in.

Edit: I just tested voltage being leaked through the tailcap. It’s 0.40V on NiMH and 0.42 on Li-Ion, just below the Chip Enable requirement. I think I may finally be onto something!

DavidEF
DavidEF's picture
Offline
Last seen: 1 day 10 hours ago
Joined: 06/05/2014 - 06:00
Posts: 7698
Location: Salisbury, North Carolina, USA

gchart wrote:
Another theory… some (most?) of these chips will pass current through the chip if the Chip Enable pin hasn’t reached the turn-on voltage (0.5V?). The TPS61221 is this way (“Pass-Through Function during Shutdown”). Perhaps on the flashlight’s low mode, the voltage reaching the PMIC is low enough that it’s not tripping Chip Enable and is instead just passing current through the IC.

Some PMIC’s have a “Load Disconnect” feature that essentially disconnects the IC if the Chip Enable is too low. Maybe that would force the main driver to shut down, giving the tailcap an opportunity to start up? I see TPS61261 has Load Disconnect (also something called “soft start” that may be helpful?), but unfortunately it’s only rated up to 4.0V in.

Edit: I just tested voltage being leaked through the tailcap. It’s 0.40V on NiMH and 0.42 on Li-Ion, just below the Chip Enable requirement. I think I may finally be onto something!


Excellent! Crown Thumbs Up

The Cycle of Goodness: “No one prospers without rendering benefit to others”
- The YKK Philosophy

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Ok, potential candidate(s) has been found: the TPS610993 (3.0V out), TPS610994 (3.3V out), or TPS610995 (3.6V out). The TPS61099x series appears to be great for ultra-low loads and features both Load Disconnect and Soft Start. And available at Arrow in 1pc increments for $1.34.

My quandary now… the output voltage is regulated up to VIN >= VOUT + 0.5V. Once VIN is 0.5V over output, it switches to a Pass-Through mode where VOUT correlates to VIN*resistance. Going with a lower output chip like the 3.0V TPS610993 will likely gain marginal efficiencies on NiMH, but it will only regulate Li-Ion at 3.5V and below – anything above that is just VIN*resistance.

Honestly though, according to the datasheet, the efficiency of input = 1.5V and 0.1mA current is ~88% for the 3.0V chip vs 86% efficiency for the 3.6V chip. It might be worth the loss of efficiency to gain the extra consistency in output regulation for NiMH vs Li-Ion and just go for the 3.6V output chip (TPS610995).

The only real downside I see is that this is a BGA (ball-grid array) package which will require reflowing – no hand soldering. Sad You can get it in a WSON package; Arrow doesn’t carry it but Mouser does.

PS – sorry if it seems like I’m talking to myself. Sometimes I feel that just writing down my ideas helps out a bit… and gives you an insight into the wild@$$ thoughts running through my head.

ImA4Wheelr
Offline
Last seen: 2 weeks 20 hours ago
Joined: 02/03/2013 - 14:51
Posts: 7925
Location: SC

^

I'm digging the way you and other contributors are posting.  I'm learning and it might trigger a helpful idea in someone out there.   This is a pretty cool thread.

djozz
djozz's picture
Offline
Last seen: 1 hour 32 min ago
Joined: 09/07/2012 - 17:04
Posts: 16541
Location: Amsterdam

I don’t understand most of it but I agree with you ImA4Wheelr!

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Ok, a new board and components have been ordered. Holy cow this IC looks TINY. Just to be clear – this is completely untested.

Wieselflinkpro
Wieselflinkpro's picture
Offline
Last seen: 3 hours 22 min ago
Joined: 05/21/2015 - 04:34
Posts: 965
Location: Germany - TLF

gchart wrote:
Ok, a new board and components have been ordered. Holy cow this IC looks TINY. Just to be clear – this is completely untested.

!{height:200px; width:200px}https://644db4de3505c40a0444-327723bce298e3ff5813fb42baeefbaa.ssl.cf1.ra...!


It seem to be nearly impossible to solder such small contacts for the IC. I think It will be very hard.
gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Wieselflinkpro wrote:

It seem to be nearly impossible to solder such small contacts for the IC. I think It will be very hard.

I agree, those contacts are super small. I’ll be reflowing it, but even then, I’m not sure if bridging will be an issue.
gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Just for fun, I put together an update of the v1.3 board, but using the WSON version of the IC instead of the tiny BGA version. Still really small pads, but it looks more manageable.

moderator007
moderator007's picture
Offline
Last seen: 7 hours 23 min ago
Joined: 12/23/2012 - 04:47
Posts: 3266
Location: North Carolina

Wow, looks like you’ll need a sewing needle to apply the solder paste. I’d like to try it, just for the challenge. Wink
Looks good gchart. Thumbs Up

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Happy Dance!

My v1.3 boards showed up today and I put some together using the TPS610995 (YFF package, a tiny BGA). It works flawlessly on both NiMH and Li-Ion and seems to be really efficient, though I still need to run some final numbers (which I will share later). I tested it in both the Sofirn SF14 and the Tool AA. No bleeder resistor needed in either! Though I did notice that efficiency in the SF14 on NiMH without the bleeder was worse; it’s like the main driver was trying to operate alongside the tailcap, though the main LED fails to illuminate. Adding a bleeder put efficiency back where it should be. The Tool AA did not exhibit this behavior.

This YFF (BGA) package is tiny and was a pain to prep. Going forward, I think I’ll be using the DRV (WSON) package.

Nicolicous
Nicolicous's picture
Offline
Last seen: 2 hours 6 min ago
Joined: 04/16/2016 - 08:28
Posts: 1505
Location: Australia
Thumbs Up Thumbs Up Beer

Nico -.-

moderator007
moderator007's picture
Offline
Last seen: 7 hours 23 min ago
Joined: 12/23/2012 - 04:47
Posts: 3266
Location: North Carolina

You did it, Awesome job gchart! Thumbs Up

DavidEF
DavidEF's picture
Offline
Last seen: 1 day 10 hours ago
Joined: 06/05/2014 - 06:00
Posts: 7698
Location: Salisbury, North Carolina, USA
Shocked Wow!

Sweet! Cool Thumbs Up

The Cycle of Goodness: “No one prospers without rendering benefit to others”
- The YKK Philosophy

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Thanks guys!

For a little perspective of size, here’s a couple between a 0805 LED and an XP-L HI.

Some rough math says efficiency is running about 80% with either chemistry.

DavidEF
DavidEF's picture
Offline
Last seen: 1 day 10 hours ago
Joined: 06/05/2014 - 06:00
Posts: 7698
Location: Salisbury, North Carolina, USA
Shocked Shocked Shocked !!!

The Cycle of Goodness: “No one prospers without rendering benefit to others”
- The YKK Philosophy

Cereal_killer
Cereal_killer's picture
Offline
Last seen: 1 month 3 weeks ago
Joined: 07/22/2013 - 13:10
Posts: 4005
Location: Ohio

Wow! You reflow these in an oven or hot air by hand?

Impressive work sir.

Edit I see above you’re doing it on a hot plate, EXTRA impressive!

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

NeutralFan
NeutralFan's picture
Offline
Last seen: 2 days 12 hours ago
Joined: 03/20/2014 - 19:22
Posts: 835
Location: Wisconsin, USA

gchart wrote:
Thanks guys!

For a little perspective of size, here’s a couple between a 0805 LED and an XP-L HI.

Some rough math says efficiency is running about 80% with either chemistry.

Sorry gchart, but I can’t see your pics. Sad

I’d rather use my flashlight around the house than turn on the lights.

gchart
gchart's picture
Offline
Last seen: 1 hour 12 min ago
Joined: 03/19/2016 - 11:57
Posts: 1950
Location: Central IL

Weird. I use a public Google Drive folder. Maybe I should just start putting them up on my server.

NeutralFan
NeutralFan's picture
Offline
Last seen: 2 days 12 hours ago
Joined: 03/20/2014 - 19:22
Posts: 835
Location: Wisconsin, USA

IDK, but I can’t see them using my MacBook with Safari. Maybe others can.

I’d rather use my flashlight around the house than turn on the lights.

Wieselflinkpro
Wieselflinkpro's picture
Offline
Last seen: 3 hours 22 min ago
Joined: 05/21/2015 - 04:34
Posts: 965
Location: Germany - TLF

I see them since the first day. WinX-PC

NeutralFan
NeutralFan's picture
Offline
Last seen: 2 days 12 hours ago
Joined: 03/20/2014 - 19:22
Posts: 835
Location: Wisconsin, USA

I can see them now on my computer. Your change worked gchart.

I’d rather use my flashlight around the house than turn on the lights.

Pages