FREE DIY open source BOOST driver!!! Tested & working!!

Tom,

Never mind, let me guess - not constant current?

What about this driver? It does not say it is an LED driver but the specs are interesting.

DC/DC Converter (Integrated Switch) - Step-Up Regulator - TPS61087 - TI.com

3mm x 3mm

• 2.5 V to 6 V Input Voltage Range
• 18.5 V Boost Converter With 3.2 A Switch Current
• 650 kHz/1.2 MHz Selectable Switching Frequency
• Adjustable Soft-Start
• Thermal Shutdown
• Undervoltage Lockout
• 10-Pin QFN and thin QFN Packages

The TPS61087 is a high frequency, high efficiency DC to DC converter with an integrated 3.2 A, 0.13 Ω power switch capable of providing an output voltage up to 18.5 V. The selectable frequency of 650 kHz or 1.2 MHz allows the use of small external inductors and capacitors and provides fast transient response. The external compensation allows optimizing the application for specific conditions. A capacitor connected to the soft-start pin minimizes inrush current at startup.

http://www.ti.com/lit/ds/slvs821b/slvs821b.pdf

The issue is constant current. And, it's switch current isn't very high. You may get 1.5A out of that if you're lucky.

If you were to make it constant current with an op-amp, it would take up a lot more space. If you were to make it constant current without an op-amp, it would be dropping 1.25V at all times, so you may only get 1A out of it.

Not sure about that, but it would be a nice IC for those direct green diodes. It's capable of 1A at 9V which is good, and 15V/500mA form 3.3V input. Perfect!

at lower outputs it might reach 1.5A output current or even more, but

have to make tests to be sure,

but I am sure that would be a good choice for future green builds

oops wolfman beat me to it

oh yeah with that feedback voltage 1.25V efficiency will suffer greatly with low-side current sensing :beer:

tsteele93 said:

Also want to add this resource in case it is helpful to anyone involved...

The LED Drivers/LCD Bias Section of the Texas Instruments E2E Support Community

Click to expand...

Regarding this resource, I found some interesting q&a regarding very similar drivers to what we need.

http://www.ti.com/product/TPS62110

High Brightness LED IC - LED Drivers/LCD Bias Forum - LED Drivers/LCD Bias - TI E2E Community


http://www.ti.com/product/LM3434

High current synchronous LED driver - LED Drivers/LCD Bias Forum - LED Drivers/LCD Bias - TI E2E Community


http://www.ti.com/product/tl4242

1W LED driver using TL4242 - LED Drivers/LCD Bias Forum - LED Drivers/LCD Bias - TI E2E Community

tsteele93 said:

Regarding this resource, I found some interesting q&a regarding very similar drivers to what we need.

(...)

Click to expand...

Those appear to be talking about buck drivers, not boost drivers.

Almost any IC, even one that is explicitly called a constant voltage IC, can be setup to run as a constant current driver. The challenge, is the if it was designed to be constant voltage, it may have a high FB voltage (0.6v+). When we re-purpose those ICs as constant current instead of voltage, we end up dropping an additional voltage equal to the FB voltage.

The LM3410 is no exception. Even though it's marketed as constant current, it's still basically just a boost regulator like all the others. We still drop an additional voltage equal to the FB voltage. With the LM3410 however, that FB voltage is 0.19V. That's really where the benefit comes from. It's not so much that the IC itself is a *called* a constant current IC. It's the fact that it was designed to have a low FB voltage that we care about.

And regarding buck drivers - 75-80% efficient buck drivers (capable of outputting .9Vin - .8V) high power buck drivers (read: capable of driving over 2A of output current) will be entering the market soon. And, a few weeks after that, an even more efficient version of the same driver will be entering the market (read: 85-90% efficient). No need to worry about the buck side of things - I got that covered

Wolfman29 said:

And regarding buck drivers - 75-80% efficient buck drivers (capable of outputting .9Vin - .8V) high power buck drivers (read: capable of driving over 2A of output current) will be entering the market soon. And, a few weeks after that, an even more efficient version of the same driver will be entering the market (read: 85-90% efficient). No need to worry about the buck side of things - I got that covered

Click to expand...

"entering the market soon" ?

Aren't they already here? I thought the X-Drive can already do that level of current, can't it?

Ah. Let me be more clear. Available in large quantities from one of the hobbyist stores, and the size of the FlexDrive.

Wolfman29 said:

Ah. Let me be more clear. Available in large quantities from one of the hobbyist stores, and the size of the FlexDrive.

Click to expand...

Oh, gotcha.

The board is FlexDrive size? Same thickness as well?

It's 9mm x 12.1mm in planar dimensions. Thickness will probably be larger: the inductor is on the opposite side of the main IC - I would have to take a look at it, because I don't have one in front of me. However, only the main IC should have to be heatsinked, if at all, and that is the tallest thing on its side.

rhd said:

Those appear to be talking about buck drivers, not boost drivers.

Click to expand...

Yes, I should have been more clear that I was sort of thread jacking for a moment. I had been searching for LM3410 sources since FE showed only one in stock. Then I found the "Q" rated automotive versions and was speculating that they might be more robust versions of the IC so I started searching for more info on the LM3410 and ended up at Texas Instruments site.

I kind of got excited at some of the driver discussions that seemed to parallel our needs, even though those are BUCK drivers and not boost drivers.

Since they are using them as LED drivers, there are circuits provided that looked like they might be usable - at least as a starting point - for a driver design.

Almost any IC, even one that is explicitly called a constant voltage IC, can be setup to run as a constant current driver. The challenge, is the if it was designed to be constant voltage, it may have a high FB voltage (0.6v+). When we re-purpose those ICs as constant current instead of voltage, we end up dropping an additional voltage equal to the FB voltage.

The LM3410 is no exception. Even though it's marketed as constant current, it's still basically just a boost regulator like all the others. We still drop an additional voltage equal to the FB voltage. With the LM3410 however, that FB voltage is 0.19V. That's really where the benefit comes from. It's not so much that the IC itself is a *called* a constant current IC. It's the fact that it was designed to have a low FB voltage that we care about.

Click to expand...

Ok, I had to read that several times but it (mostly) made sense.

I need to keep reading and probably not just on Texas Instruments forums - time to hit some books - to understand all of this better. I may continue to pick you and wolfmans brains too.

Wolfman29 said:

And regarding buck drivers - 75-80% efficient buck drivers (capable of outputting .9Vin - .8V) high power buck drivers (read: capable of driving over 2A of output current) will be entering the market soon. And, a few weeks after that, an even more efficient version of the same driver will be entering the market (read: 85-90% efficient). No need to worry about the buck side of things - I got that covered

Click to expand...

Yeah, I saw your post and I wasn't trying to offer any sort of "alternative," I was just excited to see others talking about similar LED drivers on the TI forum and wanted to share the links.

In my limited experience here on the forum and reading this thread here as it developed, in my mind we are very limited to mostly linear drivers or paying relatively high $ for the flex drive right now. This thread made it seem like (to me) that developing a new, affordable driver is a big deal and I just thought this might be useful.

This thread was so "group discussion" that I was thinking along the lines of "lots of input" rather than "one person creating their own driver."

So I wasn't trying to step on your toes. Sorry if it seemed that way.

rhd said:

Oh, gotcha.

The board is FlexDrive size? Same thickness as well?

Click to expand...

http://laserpointerforums.com/f67/teaser-blitzbuck-2a-switching-buck-driver-73108.html

Wolfman29 said:

It's 9mm x 12.1mm in planar dimensions. Thickness will probably be larger: the inductor is on the opposite side of the main IC - I would have to take a look at it, because I don't have one in front of me. However, only the main IC should have to be heatsinked, if at all, and that is the tallest thing on its side.

Click to expand...

Interesting. That's quite small. Where can I see a photo of this creation?

I actually just sent off my last prototype to Clif for him to finish his testing on it, otherwise I would nab (does that word have a silent k at the beginning? I feel like it should) a picture for you. However, the production run of boards should be here by Monday, and I expect to get the parts from DigiKey on or before Monday. Assuming all goes well with Clif, these should be available in his store soon, and I will probably introduce them on the forums with more than a teaser thread the day I get my production boards in.

Wolfman29 said:

I actually just sent off my last prototype to Clif for him to finish his testing on it, otherwise I would nab (does that word have a silent k at the beginning? I feel like it should) a picture for you. However, the production run of boards should be here by Monday, and I expect to get the parts from DigiKey on or before Monday. Assuming all goes well with Clif, these should be available in his store soon, and I will probably introduce them on the forums with more than a teaser thread the day I get my production boards in.

Click to expand...

Sounds good...
Any electrical specs and pricing...:thinking:


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Well, I have tested it up to 1.8A output (the prototype boards weren't effective enough to handle higher currents) but the IC has a high enough switching current to sustain upwards of 3A output. For this first iteration of the board it is between 75-80% efficient, but further generations (in development now) will have between 85-95% efficiency. It can handle up to 16Vin and 10Vout, but obviously it can go lower. For now they are fixed output current, but a pot is going to be added in later versions.

Pricing is up to Clif to decide, but the parts aren't cheap, so expect a bit more than $20 from Clif.

This is an amazing piece of work, well done!

One thing I'd add is a "tailbiter" aka "shut down very quickly" circuit.
This is to stop your expensive diode frying if it 1) overheats, 2) something goes awry with the driver such as low battery causing open loop operation, 3) mechanical failure.

This would also be handy for modulating the diode as well.

Circuit needn't be complex, just a single transistor with optical bridge aka optoisolator.
I'd use a MOSFET and power resistor in series as this would drop diode current below destruction levels and allow so-called "preheat" or "sub lasing" operation to allow its use for pulsed holography applications.