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ArcticMyst Security by Avery
Teaser: The BlitzBuck - A 2A+ Switching Buck Driver
- Thread starter Wolfman29
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Unfortunately, it will not run your standard LPCs with 3.7V in. This is for two reasons:
1) It's not continuous ground
2) It has a Vdrop of around .8V (need to find out the actual Vdrop).
Current is adjusted by pot for now. However, I have thought of a way that I could develop a larger version which would be pot adjustable and have less of a Vdrop. But that may come in later editions as larger, 16mm round boards. For now, I will keep these on the cheap end and do resistor adjustments.
With crappy batteries, I was drawing about 1.2A at 7.7V (with no load, I guesstimated a Vdrop to about 7.2V, but even without that, it's still decent), which would give, at the very least, assuming no internal resistance on the part of the battery, an efficiency of approximately 77%.
1) It's not continuous ground
2) It has a Vdrop of around .8V (need to find out the actual Vdrop).
Current is adjusted by pot for now. However, I have thought of a way that I could develop a larger version which would be pot adjustable and have less of a Vdrop. But that may come in later editions as larger, 16mm round boards. For now, I will keep these on the cheap end and do resistor adjustments.
With crappy batteries, I was drawing about 1.2A at 7.7V (with no load, I guesstimated a Vdrop to about 7.2V, but even without that, it's still decent), which would give, at the very least, assuming no internal resistance on the part of the battery, an efficiency of approximately 77%.
Hiemal
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How is it not continuous ground? That's really strange. Buck drivers ought to have continuous ground... at least from what I've seen almost all buck drivers have it.
How are you getting feedback through the resistor? Is it before the LD? Or after it?
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The feedback is after the diode, unfortunately. And I've actually only seen a few buck drivers capable of driving laser diodes that are continuous ground 
I've thought of the different topologies for this one, and there was no other way for me to get continuous ground out of the topology I have right now. However, the pot adjustable version I am working on as we speak will have continuous ground. The only problem, and the reason I haven't developed it yet, is because it will probably be significantly more expensive ($23 or so would be my guess) and it will be larger, which is not as appealing.
Oh, and note: these probably will work for the new Mitsubishi diodes with one battery - once I get one of the diodes in I will test it to make sure, but I designed this driver with that in mind
I've thought of the different topologies for this one, and there was no other way for me to get continuous ground out of the topology I have right now. However, the pot adjustable version I am working on as we speak will have continuous ground. The only problem, and the reason I haven't developed it yet, is because it will probably be significantly more expensive ($23 or so would be my guess) and it will be larger, which is not as appealing.
Oh, and note: these probably will work for the new Mitsubishi diodes with one battery - once I get one of the diodes in I will test it to make sure, but I designed this driver with that in mind
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Hiemal
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Ah, that's why then. To make the driver continuous ground you need to have the resistor BEFORE the diode.
Have you tried just adjusting the feedback method so that the resistor is before the diode? That ought to fix the problem, if the driver is okay with it. (I don't know if it will be, I don't know what IC you're using but the feedback method shouldn't be any different than say, the LM317 with the op amp's inverting input the "adj" or "feedback" pin)
Give it a shot I say! Worst thing that happens is the driver decides not to regulate. (driver will be fine; the reason boost drivers fail is because they try really hard to boost the voltage up so high that they effectively overvolt themselves, which a buck driver isn't capable of doing)
Have you tried just adjusting the feedback method so that the resistor is before the diode? That ought to fix the problem, if the driver is okay with it. (I don't know if it will be, I don't know what IC you're using but the feedback method shouldn't be any different than say, the LM317 with the op amp's inverting input the "adj" or "feedback" pin)
Give it a shot I say! Worst thing that happens is the driver decides not to regulate. (driver will be fine; the reason boost drivers fail is because they try really hard to boost the voltage up so high that they effectively overvolt themselves, which a buck driver isn't capable of doing)
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I've considered it. Unfortunately, that will make it significantly larger. That's why I haven't added an op-amp for less voltage drop and continuous output current. I may see it he current size board can handle the additional parts, but that would be a LOT of additional parts. Four at the minimum.
Meatball
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I'm interested in your driver. I'm also interested in seeing how high of a current it could supply after thorough testing, and what it might take to allow input voltages of up to 15V.
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Allowing input voltages up to 15V is merely a matter of changing the output and input capacitors. However, that also implies larger parts or less capacitance. With larger parts, the board will be larger, and with less capacitance, I have a feeling it will be less stable/more finicky.
However, high currents, such as 1.6A, is readily achieved. My initial prototyped board with wires everywhere on the tiny PCB is capable of handing 1.6A.
However, high currents, such as 1.6A, is readily achieved. My initial prototyped board with wires everywhere on the tiny PCB is capable of handing 1.6A.
Hiemal
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Changing the input voltage shouldn't require a change in capacitance or size. May I ask what your capacitance value is on your inputs and outputs? Less capacitance on the input actually wouldn't hurt the board too much.
Also, why would changing the feedback resistor position cause the board to be bigger? That doesn't make sense to me.
Also, why would changing the feedback resistor position cause the board to be bigger? That doesn't make sense to me.
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Changing input voltage to be 15V would result in a larger board or smaller capacitance because the capacitors I am using in this board are rated for 10V, and they are some of the highest rated capacitors for their sizes and voltages. Thus, if you wanted to increase the voltage, you would either need to upsize the capacitor size, and thus the board size (make it wider or change the circuit slightly) or use a smaller capacitance and the same size capacitor with a higher voltage.
Changing the feedback resistor to make it continuous ground would make it bigger because that would imply an external opamp which is currently not on the board, and would take up space on the board (which this circuit doesn't have!). Also, it would require a few other parts, which, again, would require more space.
Changing the feedback resistor to make it continuous ground would make it bigger because that would imply an external opamp which is currently not on the board, and would take up space on the board (which this circuit doesn't have!). Also, it would require a few other parts, which, again, would require more space.
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This is such awesome news. I really hope this pans out well because I am sort of tired of using 2 cell's for a red build
Best of luck on this all! You definitely have a customer here for when its all said and done!
Best of luck on this all! You definitely have a customer here for when its all said and done!
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Well note: this will most likely not drive a standard LPC with a single li-ion. Those have such a close Vfb to the nominal voltage of a li-ion (3.7V) that the dropout simply from feedback would result in giong out of regulation. I can test it, but I don't think it will work in this case. However, I think the next design, the one with the opamp, may be able to do it.
Hiemal
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You wouldn't need an external op amp to achieve it I'd think...? Rather wish I could test it myself.
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Pretty sure you can't just stick the FB resistor in front of the diode... then the FB pin would be seeing a voltage of Vout - Vfb instead of just Vfb.
Hiemal
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No.... the feedback pin would constantly try to see Vfb and regulate as necessary, at least that's what I'd think would happen.
May I ask for your permission to test one of your drivers?
May I ask for your permission to test one of your drivers?
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Yeah, it would want to regulate the Fb pin to the Vfb, which wouldn't be enough for the diode - it would only push .8V through the resistor which would be the only voltage leading to the diode, which simply isn't enough. Once the production run begins, we can discuss this further. Email me to discuss this? It's more of a hassle to do it on the forums.
