How-To: Add 7135 chips to a Driver Board (Stacking)

This is my first entry in my How-To series. These are step-by-step instructions for tasks related to flashlight modding. There are many different ways to do things, so I will show the methods I use that work for me.

This How-To will show how I add AMC7135 current regulator chips to a flashlight driver board. Our desire to do this is to increase the output current to the emitter. J)

This isn't really a soldering how-to, so I assume that the reader already has basic soldering knowledge and skills. There are many soldering tutorials on here and the rest of the internet.

Parts, tools, and supplies required:

  • 7135 based linear driver
  • one or more extra 7135 chips
  • soldering iron
  • helping hands
  • tweezers
  • magnifying loupe
  • solder
  • solder wick, for any solder related boo-boos

Here is a close-up of the parts. I had this driver kicking around. This is a generic version of the NANJG and it's not good. I harvested it for parts, but it's good enough for this How-To.

The 7135 chip has three pins and a tab.

Pin 1 is 'Out', where the cathode (negative) side of the LED is connected

Pin 2 is 'Gnd', which is connected to the tab, which will make things a little easier for us later

Pin 3 is Vcc, power for the chip itself. Without power, it blocks all emitter current flow. This is the pin that the driver controller (MCU) uses to control the output power.

Tab is 'Gnd', connected to Pin 2. The tab is the main thermal extraction path for the chip, so it is important for it to be connected to something to pull heat away.

On the bottom side, we can see how the tab and Pin 2 are connected:

Start by placing the driver in the helping hands. I'm adding a chip on top of the one on the right.

I start by re-tinning the tab, pin 1, and pin 3. This tends to make the process a littler smoother when making the first solder bridge.

Tinning makes freshens up the solder so it accepts new solder easier.

Prepare your iron by loading up a healthy portion of solder. Estimate enough to fill the void between the two tabs of the chips, maybe a little extra. After the first couple of tries, estimating the amount is easier.

Using tweezers, hold the new chip directly over the existing chip.

Use the soldering iron to apply the blob of solder into the space between the tabs. Raise the soldering iron vertically to get the solder to move upward to the top chip. You may need to take a few swipes in order to get it to stick. Add some solder if it looks like there isn't enough. Once it bridges align the chip before removing the iron. Once aligned, remove the iron, wait for the solder to solidify, and the chip will stay in place.

Now we move to the pins:

I hold the soldering iron vertically whenever possible. This helps because we can extract the iron vertically. Plase the tip of your solder right in between the two pins so it contacts the iron. Melt enough to fill the gap, but too much could results in unwanted shorting to nearby pins or components.

There, the first one is done:

Now repeat for the other side. And, we're done! There's no need to solder the middle pin since the tab is connected to it.

Like any soldering task, there is some practice required. You may not get it right the first few tries. Just keep trying and you'll get it. Do it enough and it becomes second nature.

Pretty soon you'll be building your very own 40 chip 7135 driver ;)

Happy Modding and thanks for reading! searchID8936

Not sure why, but just in case.

Thanks now i think i could have a go :wink:

nice guide, were building up some good info on here now :bigsmile:

I do this a few times (not 40 times and your practice would be better as mine) and I like your pictures. It will help new members a lot :slight_smile:

Relic have u tried bending the legs ? Much easier

Another suggestion that would be good on this thread is if u post how many amps the driver will be, just for say u add 3 to 8 extra chips what would the driver be at for learning perpases ?

Thanks everyone.
Nitro, I avoid bending the legs because the structure inside the chip itself is not designed to have the leads bent. The worst case is, you break off a pin. Most of the time you’ll be OK. However the stress could weaken the internal bond wire contact, leading to eventual failure. You might notice it as a flickering/varying output (intermittent) or not the current output you expected (disconnect).
For this reason, I do not recommend it. YMMV.

Thanks relic. Your tutorial is clear as a bell. A picture is worth a thousand words. I find visuals really simplify a seemingly daunting task. I know I can do this, and I will do this!
Actually, the way you don’t bother bending the pins does make sense to me. It leaves them out in the open, and more accessible to the soldering tip, while keeping it away from the chip itself.

Thanks relic for the how too. I’ve tried this a few times with no success. I guess it’s mostly due to my hands not being steady enough. I mean your photos and instructions make it sound easy. But when the driver is the size of a dime and the 7135 chips are the size of a tiny ant - and you have to solder the ant sized chips individual legs - no way for me. And I have a good mechanical ability and aptitude. But this is a no-go for me.
My poor attempts make me appreciate the fine detail work many of you on this forum can do.

thanks!!! this will be a big help for me being a first timer :slight_smile:

You’re welcome. Bending the pins does make soldering easier; if the pins stay connected to the chip.
I will do a few more of these How-To posts. The next one will be “Adding Copper Braid to Springs”. The pics are taken, I just need time for post and write-up.

If your going to do copper braids, please show me where to get some, and the proper type. Is it the same as desoldering braid?

Yes, I use desoldering braid. Easily found on eBay, Amazon, Digikey. I use one of the more expensive brands, Soder-Wick by Chemtronics. I’ll provide a link in that post.

as a new guy in this hobby II don’t really understand why you did it…yet, but I can say the tutorial shows how to it very well :slight_smile:

So if I added three chips to 3.04A driver it would become…?

Thanks Relic! Like this How to. Looking forward to your next ones!
My suggestion is to use the How to on the subject so it’s easy to search.
Like “How to Add a Copper Braid to Springs” :beer:

As posted:

:stuck_out_tongue:
In other words, increase the light output by giving the emitter more current.
Also, we rarely stop at just adding one :wink:

Not sure if these would interest people:

Those are 16x 7135 boards. 8 each side, 20mm in diameter. Each boards has a solder point for LED+, LED-, PWM and GND.

I also have 12x 7135 boards. 6 each side, 20mm in diameter. The difference is that the solder points for LED+, LED-, PWM and GND are much larger 1.5mm in diameter through holes, thus allowing for more robust wire.

Both boards were designed for a project of mine but they can be used for many things obviously. Just saw this thread and thought people might like to know stuff like this is available

- Matt

Actually, I have some desoldering braid in the mail. It’s only 1.5mm though. I thought it might come in handy to span a gap between a driver and pill. I figured I could soak it in flux, wrap it around, heat it up and add solder. Whether its a good idea or not, I don’t know…who knows.

If using the 350mA Regulator: 3 x 350mA = 1050mA, it will be 3050+1050 = 4100mA or 4.10A
If using the 380mA Regulator: 3 x 380mA = 1140mA, it will be 3050+1140 = 4190mA or 4.19A

:beer: