[retired] [WIP] 20mm single sided & 17mm double-sided ?-amp linear driver - surprisingly good!

What’s the calculation for the power rating required for the sense resistor’s?

The issue I ran into trying to use 1206’s in extremely low value’s for sense resistor’s in some of my drivers was that there just isnt high power rated 1206’s out (very very few 1W and a few more 3/4w) and there’s only one brand of those (vishay dale) and they’re VERY expensive and there isnt a large selection of them available in small quantities.

You simply calculate the power dissipated. Current multiplied by voltage drop. In this case the voltage drop is extremely low, so Power is as well. At 10A drive current you’re looking at 0.5W total (0.25W per resistor). At 20A you’re looking at 1.0W total, 0.5W per resistor. That should be easy to purchase at a fair price. ($0.40 to $1.00 each in QTY=1)

I think you may have been using a relatively high sense voltage?

I must say all designs on the forums just blow away Chinese designs in simplicity and features, even using their own stuff like QX7135 or QX7136.

Thanks Hikelite.

I should point out that anyone who plans to run 5/10/20A? through one of these should plan on heatsinking the FET properly. Potting it in epoxy is probably a good option. This driver is also compatible with the ‘remote’ boards led4power posted on OSH Park. The same wiring and cautions apply.

Also, if you setup your driver for 5A and then use the turbo bypass business to achieve 15A you will take the sense resistors beyond their ratings. I wouldn’t worry too much about it as long as you pot them. Or just don’t use the turbo bypass stuff, it’s not necessary.

If you start with the knowledge that your setup will do X-watts in DD and work backwards you can establish a safe regulated current so as not to take the sense resistors beyond spec. For example, say you know that your light will do 20A in DD. We’ll be splitting 20A between two resistors, so 10A per resistor. If we can afford a pair of 1W resistors for this project, we can use an Ohms Law calculator with that and the 10A figure and establish a resistance of 0.01 ohms. So with two in parallel we’d have 0.005 ohms, which works out to 10A regulated. Therefore for a light which does ~20A DD (turbo bypass) we’ll need to regulate at 10A for regular modes in order to keep the sense resistors in spec. As I said, I expect that we can exceed spec with potting.

I’m interested in this driver, I have lots of 7136’s (and everything else too). Would you be willing to send me your files, or at minimum your .sch and I’ll make my own board?

Here is the Eagle LBR and the datasheet link, post #39.

Err, also note that the 17mm v003 board is missing GND vias. I will be posting an updated version.

Well, I’ve just done my first test of the QX7136. It seems to operate as expected, no surprises. I used a small bank of FastTech R100 1206 sense resistors - I started with 3x and then moved to 5x.

Based on the results I got, I think these FT components are around 0.105 to 0.110 ohms. 5x of them gave 2.29A, close to the expected value of 2.5A but no cigar. About right for R105-R110 though. I measured the voltage across the bank while in operation and got 0.049v - I have little doubt that my meter is off by 0.001v and the little IC is right on point. :slight_smile:

:expressionless: = my level of comprehension
:bigsmile: = my level of glee
:beer: = my BAL

looking forward to seeing how this gets used.

I did some cleanup to the 17mm version this evening. No major changes.

  • Added GND ring vias.
  • Made LED+ and LED- vias directly perpendicular to each other and evenly spaced from the edge of the PCB.
  • Added a covered pad for LED+.
  • Straightened up the bottom a small amount.


https://oshpark.com/shared_projects/flBsJz93

OK, I did some testing.

We’ll need an FET better suited to this purpose than NXP PSMN3R0-30YLD or Vishay 70N02. Supfire’s M6 driver uses Din-Tek 30N02 (DTU30N02). Unfortunately DTU30N02 is a DPAK part, making it rather large (phsyically) for this application. I don’t fully understand what makes this part a better fit than the other FETs, but I’m working on it. One clear difference is the Threshold Voltage.

Maybe Vishay’s SiR800DP is a good option, datasheet link. Gate charge is higher than DTU30N02, but still in the range of what I think is reasonable (someone correct me!). Drain and dissipation are higher as well, not that they matter at this level (both are very high/good). Also, “Applications” listed in the datasheet are similar. :wink:

I flashed STAR momentary v1.0 on an ATtiny13A with these modifications:

  • disabled turbo
  • disabled LVP
  • switched to Phase Correct PWM (maintained standard fuses)
  • #define MODES 0,5,10,15,20,25,30,35,40,45,50,55,60,70,80,90,100,125,220,230,240,250,255

Here is my stripboard setup with a DTU30N02 and 4v input. As before I’m setup with 5x cheap R100 which achieves a regulated 2.29A

At the lowest output levels the scope’s interference is too much for the QX7136 to cope with, so output flickers and the waveform shown is inaccurate. Here is a “big picture” shot of the waveform generated at a “low” level.

As you can see, there is a lot of noise on that. Zooming in, we see the nature of the noise.

I think that the output waveform looks very agreeable. Note that the pictures show an output of maybe 2.4v! While this may not be the smoothest output ever, it’s free of the normal “off” pulses we see from a 7135 driver. I think that this driver will be much more efficient than I realized at low levels. Note that in the most zoomed in image, voltage never drops below 1.7v and does not exceed 3v.

There are a lot of modes, so I do not absolutely guarantee that these are 100% lined up, but they should be quite close. These are shots of what the controller was doing with the DRV output to the gate. Note that there is only so much juice available on DRV and the scope may have disrupted behavior some at lower drive levels.
PWM Level: 0/255
PWM Level: 5/255
PWM Level: 10/255
PWM Level: 15/255
PWM Level: 20/255
PWM Level: 25/255
PWM Level: 30/255
PWM Level: 35/255
PWM Level: 40/255
PWM Level: 45/255
PWM Level: 50/255
PWM Level: 55/255
PWM Level: 60/255
PWM Level: 70/255
PWM Level: 80/255
PWM Level: 90/255
PWM Level: 100/255
PWM Level: 125/255
PWM Level: 220/255
PWM Level: 230/255
PWM Level: 240/255
PWM Level: 250/255
PWM Level: 255/255

Nice work Wight, are you aiming to be the most prolific driver creator on BLF? :slight_smile:

Is the 7136 similar to the 7135, just without the internal mosfet? If so, can you spare one of these devices? The only suppliers I can find of 7136 are on Aliexpress, never used them dont seem to like PPal….:frowning:

Heh. :wink:

I’m not really sure how they compare from a technical perspective. Based on the output waveform in post #18 it seems that when implemented with the external FET, the QX7136 behaves pretty differently from the xxx7135. If I recall correctly a 7135 will turn fully on and off during PWM.

When used by itself the QX7136 can be set to between 10mA and 400mA using an external resistor. I have not tried using them that way, this is my first implementation with the QX7136. I don’t see much point in using them that way anyway.

I can probably help you out if you need it. That said, this eBay seller shipped promptly and packaged well, I was happy with the purchase: http://www.ebay.com/itm/370787091970 The listing says that they ship worldwide.

There are other products which are also called 7136, be sure not to become confused when shopping. The HT7136 is definitely NOT the same thing, if a person was in a hurry they could accidentally purchase the wrong thing.

OK, I’ve implemented “bypass” on my stripboard. My test setup has a lot of resistance, but it does function properly with a high-drain cell.

In order for the bypass to function, code changes were required. Basically the normal ATtiny pin-output “off” state causes a problem when hooked up to the DRV/gate stuff. Therefore we cannot use the code Werner posted over here (post#61). Instead we must keep that pin in High Impedance mode, what Atmel calls “Tri-state” or “Hi-Z”. When we’re ready to do the bypass we then put the pin in Output High (Source) mode. Table 10-1 in the datasheet shows the register setup necessary.

I’m putting the proof-of-concept code here. Sorry my code sucks so bad, it’s just a proof-of-concept. It’s not intended to provide a usable interface. EDIT: hint - the bypass is only functional in v009.c. Earlier versions are me mucking around with testing levels and things or me figuring out how we needed the pin state setup.


Side note: I also noticed that the M6 actually uses a bank of 0805’s rather than 1206 sized resistors. In order to have the same power-handling capability you must spend twice as much on resistors, but it should allow more granular setting of current. (0805’s have 0.5W handling but cost the same as the 1206’s which have 1W handling.)


EDIT: The next step is to determine dropout voltage, but I think I’ll have to build the real driver for that testing to have any meaning.

I’m an avid reader of your threads and I’m almost on the verge of beginning to gain an appreciation for what this particular driver can do.

As you may have noticed from my thread-title edit, I’ve gained a little bit more appreciation for this driver myself!

Thanks for the scope shots. Does anyone have a link to a thread in here somewhere with scope shots for 7135? Also, the QX7136 has pins on both sides, are they the same pin on both sides (making it a 3 pin component) or are they actually different pins (making it a five pin component)?

Is it correct to assume that you can skip using PWM and use a pot as a sense resistor and thus have output control? (always wanted that :-) )

No, at least not with a conventional potentiometer. Two Three things stand in your way: 1. The pot must be able to dissipate enough power (0.05*X.X amps). 2. The pot must be extremely low value, we’re talking about a pot that’s has a sweep like 1 ohm to 0.0025 ohm or something. +3. I think that wiring in a pot as a sense resistor could introduce a lot of extra wiring resistance and things and give unexpected results.

Is your interest simply in having a knob to freely adjust brightness, or are you specifically interested in using a potentiometer in place of a sense resistor? If you just want a brightness knob, I did recently start a little bit of work on that. Our discussion in this short thread about the classic Lambda VaraPower driver led me to start hacking up some code. I posted about it in the STAR firmware thread in a small handful of posts strewn between 670 and 715. Most notably #688, #712, and #715.

I’ve set that aside for the moment, but if all you want is a driver which lets you adjust the brightess freely/continuously with a knob then that will be easy. I’m shooting for a driver with LVP which lets you adjust the brightness with a knob.