7135 drivers with higher voltages revisited

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mattthemuppet
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Rufusbduck wrote:
Feel free to chuckle if you think I’m in over my head.

you might be in over your head, but you’re a strong swimmer!

ImA4Wheelr
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I mistakenly posted the following questions in a different thread:

http://budgetlightforum.com/node/19853?page=1#comment-415934

I meant to post here because this is were the original idea was posted.

I would like to try the mod in Post 22 above. I want to use it to drive an MG-T2 with 2 li-ions or 6 Ni-Mh’s. I’m not following the bit about adding a resister with a switch to cut it (the resistor) out at lower battery voltages. Would the resister part be necessary for my app which has fairly limited difference between supply voltage and Vf?

Secondly, wouldn’t the 2 volt dropout from the 78L05 serve as a low voltage cut off? 7 volts comes out to 3.5v for each cell.

comfychair
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Not needed. Remove & replace the original diode with a ~100 ohm resistor, and put a zener diode across (in parallel with) the top of the capacitor on the other side of the board. That's it, works fine.

I have pictures of what to do posted here somewhere, but with the forum's method of only listing threads started instead of all posts in all threads, it's a serious pain to go back and find stuff later, like now...

PilotPTK
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comfychair wrote:
but with the forum's method of only listing threads started instead of all posts in all threads, it's a serious pain to go back and find stuff later, like now...

Click "My Account"

Click "My Posts"

Click "General Settings"

Change "Content" from "Node" to "Both"

Click "Apply"

I am currently extremely busy with work. Please do not expect a response from me quickly. I will be dropping in as time permits, but the amount of time I can dedicate to responding to topics and PMs is very limited.

ImA4Wheelr
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Thanks comfy. I’ve seen your mod and it is great. Haven’t tried it yet, but will eventually. I already have some of these regulators and want to give this approach a shot.

Rufusbduck
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ImA4Wheelr wrote:
I mistakenly posted the following questions in a different thread:

http://budgetlightforum.com/node/19853?page=1#comment-415934

I meant to post here because this is were the original idea was posted.

I would like to try the mod in Post 22 above. I want to use it to drive an MG-T2 with 2 li-ions or 6 Ni-Mh’s. I’m not following the bit about adding a resister with a switch to cut it (the resistor) out at lower battery voltages. Would the resister part be necessary for my app which has fairly limited difference between supply voltage and Vf?

Secondly, wouldn’t the 2 volt dropout from the 78L05 serve as a low voltage cut off? 7 volts comes out to 3.5v for each cell.


The 78L05 is only regulating the supply voltage of the mcu and is not otherwise involved in the led power circuit. Since the mcu will operate down to under 3V(1.5V/cell), there is a risk of over discharging the cells unless you pay attention to the led and recharge the cells when the light begins to dim on high(<6V or 3V/cell). With an overdriven led this should happen at a higher voltage but at lower output there’s still a risk of over discharging the cells. The switch and resistor was a means of burning excess voltage over what the 7135 chips could handle and when the battery voltage drops to something manageable, the resistor would be bypassed, allowing the 7135 chips to handle the remaining load. Probably not necessary with 2cells/2xmls or 2cells/1mtg but may be needed for 3cells/3leds and certainly for any more than that.

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

Scott

ImA4Wheelr
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Thank you Rufus. So the regulator will just quit regulating below 7v and just let the current pass. Makes sense.

Thank you for your opinion on necessity of the resistor/switch. It’s worth risking inexpensive 7135’s to not have to develop a separate resister circuit with a mechanical or automated switch of some sort.

Rufusbduck
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I’m not an EE so I don’t know what happens to the 78L05 below minimum but there’s another chip, the LD2981 that works down to 5V and is the same package size and pin layout. It would save a boatload of effort if a nanjg driver were layed out with this chip located next to the mcu. With more mtg mods going on it might make more sense now.

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

Scott

texaspyro
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Rufusbduck wrote:
I’m not an EE so I don’t know what happens to the 78L05 below minimum but there’s another chip, the LD2981 that works down to 5V and is the same package size and pin layout.

Check out the LM2936, it has a VERY low quiescent current and a 0.2V dropout.

The 7805 chips typically look like a 2V dropping diode at input voltages below their dropout voltage.

ImA4Wheelr
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Rufusbduck, I'm finally going to try your idea in Post 45.  I'm not going to surface mount, but I am going connect the L78L05 to the same point as in the below pic. 

Question.  Will the 5v regulator consume power all the time (i.e. even when light is off)?  I can test this myself, but was wondering if you know right off the bat.

Rufusbduck
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No, only when the circuit is complete. It does the same thing as the Zener mod but has slightly wider input voltage range so it could work with 2s liion – 2s led, 3s liion – 3s led, or 2s liion – MT-G2. The LD2981 will work for any of those. The L78L05 has a slightly higher voltage drop and works better on 3S mods. DrJones was the one who pointed me towards them way back when.

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

Scott

ImA4Wheelr
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Thanks Rufus.  Sorry, I should have been more specific.  I was thinking momentary switch situation where battery circuit is always complete.  Kind of figured it wouldn't use juice when the cells are disconnected.

Thanks for the info on the lower voltage drop units.Smile

texaspyro
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Yes, it will draw large amounts of power. And not give any reverse voltage protection. Try an LM2936.

ImA4Wheelr
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Thanks TexasPyro.  So if I did use one of my L78L05's, it would need to be a light that I can lock out.  Kind of expected  that, but hoped other wise.

Rufusbduck
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The way I wire it still has reverse protection since I use the polarity diode as the jumper from B+ to the input pin of the voltage regulator.

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

Scott

Rufusbduck
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Old thread I know but resuscitated due to current application.

texaspyro wrote:
Yes, it will draw large amounts of power. And not give any reverse voltage protection. Try an LM2936.

The LM2936 has built in reverse polarity protection and a dropout of .2v and is available in sot223.

The LD2981 doesn’t have reverse polarity but dropout is between .007-.170V and quiescent current is 80 microA no load. It’s a sot89 package.

Both require capacitors on input and output.

Using an FET in place of all 7135 chips and adding 28.7k resistor to regain low voltage protection.

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

Scott

ImA4Wheelr
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I keep starting down this path (LDO voltage regulation) and then end up going off the rails.  I want to implement LDO for a 4S configuration.  Based on the data sheets, the LM2981 out.  The LM2936 can take up to 40 volts.  So it seems the way to go.  It doesn't appear to come in a SOT23-5 package, which is a bummer if one wanted to use wight's LDO board.  Guess air wires will be the solution until I get a chance to build some boards in Eagle.

I'm ordering some 5v LM2936's and 81's right now.  So I'm all ears if anyone has any relevant suggestions.

EDIT: Ended up just ordering some LM2936's in the TO-92 package as it seems they would be easier to air wire.  I need to figure out what size/type caps I will need for the input cap.  The data sheet also says the device's overall input cap can be relied on if within 3 inches of the LM2936, but encourages using a input cap regardless.  So maybe I can skip that cap.

The data sheet says proper ESR is critical on the output cap.  It says a resistor value of 500-mΩ to 1-Ω must be used in series with output cap for ceramic caps to simulate ESR.  It calls for a minimum 10 μF cap for the 5v version.  I'm assuming the 10 μF smd's we use on our DD drivers is ceramic.  So it appears I don't need to order any caps.

Rufusbduck
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What’s the series Vf of the LEDs?

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

Scott

ImA4Wheelr
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^I'm assuming your asking that question because this thread is primarily about 7135's being used at higher voltages.  My current project does not involve 7135's.  I'm asking the above in this thread because in the process of driving 7135's to higher voltages, you also did some experimentation regulating the power to the MCU.  It's the best discussion I'm aware of on the topic in BLF threads.

To answer your question, the Vf will vary depending on the mode the driver is in.  It will be a DD driver powered by 4S Li-ion cells.  The load will be the equivalent of 4S high power white LED's (XHP50 configged for 6V - XM-L2 - XM-L2).

I'm hoping to use the above LDO regulator in several different momentary drivers that I am currently using.  I'm having too many close calls with draining cells too low.  For example, I would also like to mod my HX-1175ba drivers (Buck) that are all set up in momentary switch lights.  I still intend to lock them out, but I would like to give the cells a fighting chance should I forget to lock a light out.

If all goes well with them, I would like to design some OSH Park boards for momentary switch setups.  Hoping someone will beat me that though because I am way early on the Eagle learning curve.

Rufusbduck
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Just curious. An LDO regulator should handle the mcu no problem. Have you changed the R1/R2 values to accommodate the higher voltage. Don’t forget the voltage divider needs to be connected before the regulator input. If you’re using pwm to control led output then you might need those caps on the regulator input and output anyway. Obviously I’m no engineer, just enjoy puzzles.

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

Scott

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I will when I build the DD driver.  For the HX-1175b1's (with Attiny13a swaps in them), I added LVP voltage dividers.  I don't recall the resistor valus for the 3S light.  I did 2 4S lights, both set up the same resister values and FW settings.  The most recent 4S here and I used 100K for R1 and 5.1K for R2.  The voltage dividers are connected straight to the Batt+ and Batt- with no diode.  Currently, the LVP values are:

#define ADC_LOW    110
#define ADC_CRIT    100
#define ADC_DELAY  188

The above will probably be changed after the cells are run down several times.  For some reason, I get really weird results when I try to simulate low voltage with cheap bench power supply.  Probably has ripple issues that is confusing the mcu.  It does help me narrow down the resistors and FW settings some though.  I have the same set up as above (except 4S, not 2P4S) in my Crelant 7G10 and it finally just started steeping down from the highest mode.  When I check the cells without load they are just above 13 volts.  But when I turn the light on in high mode, the battery pack sags immediately down to 11.xx volts.  The light steps down to the next mode and voltage jumps back up.  So I'm early on seeing how the FW settings are doing in real life.

Rufusbduck
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I’m curious to see how the mcu differentiates between voltage sag on high vs low voltage cells on low. Could this be solved by coding to compare against different values in different modes? Might need a bigger mcu for that or use a second voyage divider on a different i/o pin. Just wagging here.

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

Scott

ImA4Wheelr
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^ I here you.  In this case, the stepping down from high only to start with is great.  The light pulls 9 amps on high.  So the light stepping down to level 6 (of 7) will let me know the cells are starting to get low and put me at a level that will help me more likely get home before the cells die.  After the cells get lower, it will start stepping me down to level 5.  Seems a pretty good system to me.

I am curious how the driver will act with the new LDO regulator feeding the Attiny13a.  Right now, the Vcc feed to the MCU drops as the battery pack voltage drops.  If the new LDO regulator provides more consistent voltage, it might change the above described behavior. Just have to wait for that slow boat from China to find out.

Thanks for the info you provided in this thread.  It has tremendously speed up the research and decision process.  I'll report back on how the L2936 works out.  I'm betting (and hoping) it will be as you expect.

Rufusbduck
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Somewhere around I think I have a few L78L05 sot-89 chips rated at 30V input. Is that sort of what your looking for?

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

Scott

ImA4Wheelr
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^ Thanks for the offer.  I have some too.  I bought them a long time back after first reading this thread.  This time, I'm looking for the lowest parasitic drain I can find for 4S cells.  I like the data sheet for the L2936 you discussed above and have ordered some.

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