Erdabyz's switching laser drivers

HIMNL9 said:

Just as suggestion.

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Well... 4.7ohm is still too much. And germanium transistors tend to be expensive and they don't last very long. With a proper current sensing amplifier you can use 0,1 ohm or less precission resistors. Those devices have fixed gain so, instead of using a pot to adjust the gain as we would do if using a general pourpose op-amp, we use that potentiometer to divide the output voltage. A common op-amp would be great too but that requires some extra components that make the driver bigger... I have some TSC101A from ST electronics that would do the job.... but they require 4V to work so ...
I have to find some that would work at 3V or less and that way I could do a great driver for 8x's with LT1930's. They are the smaller and simpler switching IC's i've found that would be just perfect for driving 8x's from a single li-ion.


Oh, other thing I forgot, your configuration has a resistor in series with the diode, meaning that the driver would have to provide more voltage. So, if going to use a resistor in series with the diode, it HAS to be a very low value, so it won't increase too much the voltage the driver needs to supply.

I know 4,7 ohm is still too much ..... i'm not making critic about your design, it was just an example ..... same current that with your 12 ohm, more or less, but with less ohm and less dissipation, just adding a transistor (and if i had a GE one, instead a SI one, i bet that same regulation is possible with 1.8 ohm or similar)

erdabyz said:

Oh, other thing I forgot, your configuration has a resistor in series with the diode, meaning that the driver would have to provide more voltage. So, if going to use a resistor in series with the diode, it HAS to be a very low value, so it won't increase too much the voltage the driver needs to supply.

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ehm ..... being sincere, also your 12 ohm resistor is in serie with the LD .....

Anyway, i think it can be improved, using an amplifier, as you say, cause this way, you only need to regulate the gain (or the voltage you read, both the solutions are good, imho) ..... only, the op amp require a reference voltage ..... this need or an external one, or a regulator that already give you a fixed one (but this require a different regulator, or at least one more pin )

By the way, what about LT6106 / LT6107 from Linear Technology ? ..... they start from 2,7V power supply, and apparently can use the same power on exam as power supply line, and become gain-programmed with 2 resistors ..... can simplify a lot the schematic, compared with op amp, network, reference and all the rest needed

ehm ..... being sincere, also your 12 ohm resistor is in serie with the LD .....

Anyway, i think it can be improved, using an amplifier, as you say, cause this way, you only need to regulate the gain (or the voltage you read, both the solutions are good, imho) ..... only, the op amp require a reference voltage ..... this need or an external one, or a regulator that already give you a fixed one (but this require a different regulator, or at least one more pin )

By the way, what about LT6106 / LT6107 from Linear Technology ? ..... they start from 2,7V power supply, and apparently can use the same power on exam as power supply line, and become gain-programmed with 2 resistors ..... can simplify a lot the schematic, compared with op amp, network, reference and all the rest needed [/QUOTE]

Yeah, it's also in series, but for any strange reason I still can't explain, the driver works perfect even where you might think that, with the diode and the resistor, it should provide about 5V for the LD + 1,235V from the ref, which would mean 6,235V, when the driver has an absolute maximum of 5,5V.
I did some simulations and saw that a design like that would work and yeah, the real one did work. I'll have to measure the voltage between the out and ground when working. I haven't measured it yet, that way I could see if it's 6,2 V or less.
I'm not saying that my design is the bestr or anithing like that, i'm just saying that it does work. It can perfectly be improved, and your design is a good improvement because it also provides a way so the diode has the same ground than the regulator.

I'll check your op amps later, but I have to say that there's not very much room for "solderable at home size" resistors in a design that must fit inside an aixiz module. In fact, a 0805 resistor uses almost the same space than the regulator IC. So, if we can find anything that just requires a single pot, it would be perfect.

wow i wish i knew the language you guys are talking lol

erdabyz said:

Yeah, it's also in series, but for any strange reason I still can't explain, the driver works perfect even where you might think that, with the diode and the resistor, it should provide about 5V for the LD + 1,235V from the ref, which would mean 6,235V, when the driver has an absolute maximum of 5,5V.
I did some simulations and saw that a design like that would work and yeah, the real one did work. I'll have to measure the voltage between the out and ground when working. I haven't measured it yet, that way I could see if it's 6,2 V or less.
I'm not saying that my design is the bestr or anithing like that, i'm just saying that it does work. It can perfectly be improved, and your design is a good improvement because it also provides a way so the diode has the same ground than the regulator.

I'll check your op amps later, but I have to say that there's not very much room for "solderable at home size" resistors in a design that must fit inside an aixiz module. In fact, a 0805 resistor uses almost the same space than the regulator IC. So, if we can find anything that just requires a single pot, it would be perfect.

Click to expand...

Uh, yes is strange ..... being the FB pin kept at 1,235V, theorically it must fail, cause referred to GND it's 6,235V to keep ..... if the LD is 5V FV ..... ah, well, mysteries of electronics

I've seen at datasheets (still not get my samples, also if requested 2 weeks ago ), that LT6107 can be the better choice, anyway it need at least one sense resistor (ofcourse) and one current-to-voltage resistor (perhaps all these amplifiers have only open-collector current source outputs, so need at least a resistor for convert the out from current to voltage) ..... and, probably, for the use we need, is enough to use a 150 / 200 ohm trimmer for set the input ..... or, maybe also better, a fixed resistor at the input and a trimmer at the output ..... cause, after all, using it in the configuration we need, is not the use they are designed for .....

I mean, all these ones are designed to be measure probes, giving an output that is proportional to the current passing through Rsense, so, a potentiometer can be used in 2 ways ..... or at the input, for vary the gain, so the output can read 1,235V at the desired current, or at the output, so the voltage can be set through the trimmer at 1,235V when the current is at the desired value ..... both the solutions have pro and con, imho, but considering the high impedance of the FB input of the MAX1723, probably the better solution is using a 10Kohm trimmer at the output of the amp, and drive directly the FB pin with the central of the trimmer ..... i know, it's not a professional design, but we're speaking about hobby level product, so i think it can be acceptable.

Also, must considerate that the maxixum output current of the amp is given at 1 mA, so, on 10Kohm, with 0,1ohm of Rsense and the gain set to 100 with Rin=100, must have an output of 1 V each 100 mA of load, at max ..... not too much to regulate ..... maybe better try with an Rin of 200 ohm, or also just 150, for 2V (1,5V) each 100 mA of current, so the trimmer can regulate it better in the full range of the MAX1723 .....

Something like this





@ john_lawson: don't be preoccupied, you also can learn how to speak in this language ..... all that you need to renounce, is your mental health ..... (J/K )

Oh YESSS!! Maxim again saves our day!
http://datasheets.maxim-ic.com/en/ds/MAX4173-MAX4173T.pdf

Now the only problem is what would happen if the battery drops below 3V and the amplifier stops working.... because if it stops working and starts sending a "random" voltage to the feedback pin, lower than required, the current would start increasing.... killing both the diode and the driver.

Adding extra undervoltage protection would mean 3 IC's in the driver, increasing the cost and the space required for it.

EDIT:
Hadn't seen your last post HIMNL9, I think I'm gonna simulate your design in LTspice to see what happens .
EDIT2:
I reminded why I didn't like LT6106.... It's because it must take power from the switching regulator, and I think that wouldn't work because the output voltage of the regulator in current source mode is set by the voltage drop in the component that has less voltage drop. If the op-amp has less voltage drop than the diode, it would make the driver set that voltage. So I think we need something like the 4173 which has separate power, meaning that you can power it with the battery while sensing current from the regulator. However, i'll simulate your design later and i'll tell you what happens.

erdabyz said:

I reminded why I didn't like LT6106.... It's because it must take power from the switching regulator, and I think that wouldn't work because the output voltage of the regulator in current source mode is set by the voltage drop in the component that has less voltage drop. If the op-amp has less voltage drop than the diode, it would make the driver set that voltage. So I think we need something like the 4173 which has separate power, meaning that you can power it with the battery while sensing current from the regulator. However, i'll simulate your design later and i'll tell you what happens.

Click to expand...

Uhm, maybe, but is possible that this one is ininfluent ..... after all, with a supply range from 2,7 to 36V, and a supply current around 65 microamperes, it probably don't interfer too much in that sense.

Damn, must decide to get some *spice or some other simulation software, first or after

john_lawson said:

wow i wish i knew the language you guys are talking lol

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I wasn't joking when I said he was a genius lol, he is 17 years old!

I recently ordered some LT1110 IC's. Just wondering if anyone here has used this IC before and can give some tips. Looks like it may be a decent IC.

Sorry for give you a bad news, but i tried them, too, and never got enough current ..... for get some decent current from them in boost configuration, you need inductors at least 10 times bigger than other models, or use an external switching transistor.

Or, at least, i was not able to make them work as i want

Side note: my PHR diodes really seem to like the max711 IC. I have been running it @ 5.6v and 150ma with about 5-6 hrs. on it now. I wish I had an LPM so I could provide some hard data, but this is defiantly the highest output PHR I have tested out of 11 BY FAR! It will light a match @ 13ft instantly! Also, I'm not seeing any degrading when I de-focus the spot, as I have experienced in the past when pushing PHR’s to higher currents with DDL drivers. It's also very efficient apparently, since I haven’t had to charge the battery at all yet (rcr123 still reading 3.68v under load, was 4.2 when installed). An anomaly? Not sure, but it's running strong!

HIMNL9 said:

Sorry for give you a bad news, but i tried them, too, and never got enough current ..... for get some decent current from them in boost configuration, you need inductors at least 10 times bigger than other models, or use an external switching transistor.

Or, at least, i was not able to make them work as i want

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Cool, well thanks for the heads up!

Ramsey_innovations said:

Side note: my PHR diodes really seem to like the max711 IC. I have been running it @ 5.6v and 150ma with about 5-6 hrs. on it now. I wish I had an LPM so I could provide some hard data, but this is defiantly the highest output PHR I have tested out of 11 BY FAR!

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IIRC... there is a guy on the forum than manufactures and sells LPMs...
I believe it has a PC Data Logging Interface and you can print out
Power Graphs...


Jerry

lasersbee said:

IIRC... there is a guy on the forum than manufactures and sell LPM...
I believe it has a PC Data Logging Interface and you can print out
Power Graphs...


Jerry

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Thanks Jerry,
I'm just waiting for some income. I'm a full time college student at 26 trying to make ends meet. I will be able to invest in one come late next month. If I had a little $ to invest I'd be in Tampa (an hours drive for me) picking up that DNA sequencer thats only $75 now:yabbem:

Ramsey_innovations said:

..... picking up that DNA sequencer thats only $75 now:yabbem:

Click to expand...

do you mean this one

GENOMYX LR DNA SEQUENCER - eBay (item 220468148172 end time Aug-24-09 15:49:01 PDT)

or this one ?

PERKIN ELMER ABI PRISM 377 DNA SEQUENCER - eBay (item 370246868158 end time Aug-24-09 15:46:01 PDT)



(hell, how much i envy peoples able to collect all those funny surplus things ..... here, no way at all )

Yeah, I know they have two of them. I wasn't sure if the genomyx contained an argon, I tried to google it for a bit with no success. But the prism 377 is pretty much a sure bet.