Teaser: The BlitzBuck - A 2A+ Switching Buck Driver

Wolfman you are right, you can't just stick the set resistor on the high side. The FB pin reads in relation to ground so that won't work.

Can't wait to see your driver!

Yup! Anyway, I sent my physics professor an email so I should be able to get access to the oscope on Wednesday morning. Gives me time to finish my paper that's due tomorrow night ^_^

Nice work can't wait to see it :beer:

-Anthony

I'm sorry May I repeat my question, can it drive 2-5W IR diode from 1x18650 cell?

I'm sure it can I just got back from physics today with tests on the oscilloscope! Turns out, at most, 50mA ripple when in regulation, 100mA ripple when just getting out of regulation. But the ripple is so quick, I doubt even a diode would notice it - we are talking much faster than 1MHz.

I'll update the main post later with pictures!

Wolfman29 said:

I'm sure it can I just got back from physics today with tests on the oscilloscope! Turns out, at most, 50mA ripple when in regulation, 100mA ripple when just getting out of regulation. But the ripple is so quick, I doubt even a diode would notice it - we are talking much faster than 1MHz.

I'll update the main post later with pictures!

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Wow! Nice work that's great statistics :beer:

-Anthony

It would be good if it run the IR diode on 2000mA! But this diode is case positive, if you check it's not a problem to run the diode on negative voltage I'm in. :yh:

Hmm. Well, that's a problem - this driver isn't continuous ground, so all diodes must be isolated :\

I cant argue about the design but I am interested too. I havent even seen a buck so I cant say but it sounds like it's worth a try. If you want a continuous ground just join them. allway's worked here so far Just like the microboost.. you dont have to isolate anything. The one I'm worried about is the 9mm 808 case+ ...

Kizdawg said:

I cant argue about the design but I am interested too. I havent even seen a buck so I cant say but it sounds like it's worth a try. If you want a continuous ground just join them. allway's worked here so far Just like the microboost.. you dont have to isolate anything. The one I'm worried about is the 9mm 808 case+ ...

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That's awful advice. You can't do that.

I don't know what Wolf's circuit is, but don't you think that if it COULD BE made continuous by just "joining them", that Wolf would have joined the V- and L- on the PCB ?!?

On many boost and buck drivers, current sensing is taking place between the V- and L-. So if you "join them", you bypass current sensing (or effectively give the regulator a 0.00000000000001 ohm resistor, causing it to try and boost current infinitely high). On a boost, you might just get pulsing or horrible performance, because most boost drivers can't actually kick out the 2.2A+ that you'd need to fry a 445. On a buck, you're likely to have a scenario where the driver actually has the ability to shoot way more current at the diode than it can handle. Get rid of current sensing by shorting the V-/L- and a driver like this is likely to dump 3A+ into your 445.

really? I hate to say sorry again... I havent had to isolate anything. I connect the - to - the + to + and the case pin to the - on the Vin - in side. I will try not to give any advice in the future. I just want to run away and make lasers... Why was that bad advice?

/kizdawg crawls back under the popcorn machine and cowers in shame...

Kizdawg said:

really? I hate to say sorry again... I havent had to isolate anything. I connect the - to - the + to + and the case pin to the - on the Vin - in side. I will try not to give any advice in the future. I just want to run away and make lasers... Why was that bad advice?

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What you've just said here ^ is correct. Don't beat yourself up!

BUT - it's only correct if you're using 405, 445, or 635 diodes. Those are already isolated from the case. IE, they're case neutral. Their case pins aren't attached to any part of the emitter themselves. The case pins are almost the same as if you just soldered a wire to the inside of your host walls.

It's a different story with IR diodes, because they are not isolated from the case. The case pin is actually continuous with the (+) pin. Thus, you would need to isolate them to use a driver without a continuous + or -. (preferably continuous +, but Jib had a creative way for making continuous ground drivers work with case positive diodes too)

Also, I would clarify that what you described when you said:
1) "If you want a continuous ground just join them"

Isn't actually what you described when you said:
2) I connect the - to - the + to + and the case pin to the - on the Vin - in side.

In comment 2, all you're doing is taking the battery (-) feed from the tailcap, via the case pin, and inputting it into the driver. Then you're taking the driver's (-) output and sending it to the laser diode emitter. But the (-) in and the (-) out are never actually continuous in this scenario. Regulation is happening in between. They're not a single connected feed the way you've described it. So you're not actually doing thing #1, which is what I was warning against.

This is good. You should never do thing #1 with a non continuous driver

You just want me to run away... and I'm not there yet... maybe after 3W...

So why not just put the battery in backawrds? and or bla fgt Why do we need 808's again? to make nice yellow orange and green? Sell me a Green diode RHD? Osram? Price? I Promise I wont dissapoint you again...

I need another MOD3 do you have any left? Er I need a FlaminPyro press addon to press 3.8mm diodes!

Kizdawg said:

You just want me to run away... and I'm not there yet... maybe after 3W...

So why not just put the battery in backawrds? and or bla fgt Why do we need 808's again? to make nice yellow orange and green? Sell me a Green diode RHD? Osram? Price? I Promise I wont dissapoint you again...

I need another MOD3 do you have any left? Er I need a FlaminPyro press addon to press 3.8mm diodes!

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If you use the battery backwards, you still need a driver with a continuous positive, because the battery (+) will feed the diode directly, as well as (presumably) having to feed a (+) input on the driver.

your right I think I popped another 808... I dont understand elecricity! the new GQ-A305D freaks me out every time I use it on a diode. I look at a build and I understand it but getting tehre is another thing

Kizdawg said:

your right I think I popped another 808... I dont understand elecricity! the new GQ-A305D freaks me out every time I use it on a diode. I look at a build and I understand it but getting tehre is another thing

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When you put the battery case positive (with a case positive diode), it is the same thing as by-passing your driver and feeding your diode direct from the battery.

Unless you happen to be using a driver that regulates through the negative side...