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DC/DC boost drivers question

Tabish

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How many good/small ones exist?

Such as the flexdrive.

Is there a cheaper alternative for the flexdrive???


No offence Dr.lava, you got an awesome driver, but it's really pricey for me.
 

bobhaha

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hey mo, do they work the same way as the flexdrive or are these simular to a linear driver.. is there any review or tut on this driver.. i couldn't find any...

thanks in advance -Adrian
 

lazerov

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I have 4 of these Rayfoss drivers. They are boost drivers, not linear. One of them drives a PHR@100mA from 2xAAAs. Works with 2 NiMHs, too. Another one is pushing a 4x diode with 160mA, powered from one 3,6V CR123. I don't think these are better than a Flexdrive, but they are cheap.
The picture on the Rayfoss site correctly shows the driver pin-out. It matches the pin-out of a blu-ray LD. There are two things you must note:
The + input of the driver is taken via the case pin of the diode. Therefore, the module becomes case positive. You can cut that pin and solder the + wire directly to the driver.
You should put additional 47-100nF SMD capacitor between the anode and cathode of the laser diode. This is because the driver has some spikes in the output voltage (checked with oscilloscope). Otherwise you risk killing your diode.
 

lazerov

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Some spikes? what degree of spikes?
About 0,7-0,9V peak-to-peak. The driver has a tantalum filter capacitor, but I don't think it can filter the relatively high frequency the driver operates at. Adding small SMD capacitor at the output overcomes the problem.
 
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a 0.7V peak when it should deliver what? I mean a 0.7V peak on 10V is not a big problem, it is however in a 3V system ;)
 

lazerov

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I made a small drawing to illustrate what I'm talking about:

The red line displays the output voltage. In this case the output voltage is 4,5V. With a perfect driver (... and perfect load) it should be a flat line. The picture is illustrative, so in reality the spikes are much thinner. It will not kill a diode instantly. However these spikes should be removed. A 47nF cap makes the line nearly flat.
 
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Tabish

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Larry has one of these $6 boost drivers in a 6x laser.
Rayfoss
Hmm. That seems PERFECT for the PHR. I mean, it's fairly cheap and non-linear too.


No pot on it ?? How do we set it's current ?

Where can I get a 47nF cap for cheap ?
 
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lazerov

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Ummm, no pot on it ?? How do we set it's current ??????
There is current setting resistor on the PCB. To calculate the resistor value divide 120 by the needed current. For example 1,2Ohm resistor gives 100mA current, 1,0Ohm - 120mA and 0,68Ohm - 180mA.

I think you can get 47nF cap at most electronics shops. They should not cost more than few cents each.
 
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Tabish

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Ahhh ok. Does the board come with a resistor ???

Or do I have to solder and replace it.
 

lazerov

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Ahhh ok. Does the board come with a resistor ???
Yes, it does. You can ask them to solder the appropriate resistor. BTW, this driver comes without switch. You should ask for it too, but I'm not sure about this.

EDIT: fixed the "button" issue :D
 
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Tabish

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Button?? You mean like a small clicker button for pen hosts ??

Btw, I assume it can fit inside the aixiz module ?

Last question, is the current the output current? (as in what the diode receives)
 
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