Which driver is better?

chipdouglas said:

has any body actually had a sucessful phr build with a rkcstr driver with only inputing 6 total volts? in my experiences this is not possible. but maybe i read this thread wrong?

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You are correct, with a 2.3V dropout, a rkcstr driver would need 7.3V to operate 5V blu-ray in a steady current regulation state. The recommendation is to use 2 rechargeable li-ion cells in series with a rkcstr in a blu-ray build. Below that and the power drops off. Also, (I didn't see this mentioned) the rkcstr will be getting warm-hot dissipating(wasting) 408mW of power (2 li-ion, 120mA blu ray) at full battery charge versus 72mW for the FlexDrive (1 li-ion 120mA blu-ray) which translates into at least 50% longer run-time per charge with the FlexDrive. Typically if you are able to use 1 long li-ion rechargeable with a flex instead of 2 shorter li-ion rechargeables with the rkcstr you will end up getting 300% greater (3x) the run time per charge with the flexdrive.

That said, The FlexDrive can't be used with battery voltages over 6V (know your nominal and peak ratings) and as has been said the soldering areas are smaller and harder to work with.

drlava said:

You are correct, with a 2.3V dropout, a rkcstr driver would need 7.3V to operate 5V blu-ray in a steady current regulation state. The recommendation is to use 2 rechargeable li-ion cells in series with a rkcstr in a blu-ray build. Below that and the power drops off. Also, (I didn't see this mentioned) the rkcstr will be getting warm-hot dissipating(wasting) 408mW of power (2 li-ion, 120mA blu ray) at full battery charge versus 72mW for the FlexDrive (1 li-ion 120mA blu-ray) which translates into at least 50% longer run-time per charge with the FlexDrive. Typically if you are able to use 1 long li-ion rechargeable with a flex instead of 2 shorter li-ion rechargeables with the rkcstr you will end up getting 300% greater (3x) the run time per charge with the flexdrive.

That said, The FlexDrive can't be used with battery voltages over 6V (know your nominal and peak ratings) and as has been said the soldering areas are smaller and harder to work with.

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So true drlava. So many in this hobby only care about being CHEAP when it comes to the driver, despite it being the very lifeline for their laser diodes health. They totatally overlook the poor efficiency of the LM317 or similar regulators for this application. They also tend to overlook how most of the available LM317 type drivers don't even incorporate the proven basic sound design practice of incorporating bypass capacitors to inhibit parasitic oscillation. Sure, they may be simple and/or cheap, but I would never trust a potentially expensive laser diode to a simple or cheap driver. Especially one that tends to go into self-oscillation as the input to output voltage ratio changes. The manufacturers never intended for those simple regulators to be run without bypass caps. The application notes do not show them because circuit designers are SUPPOSED to know to always use them.

Keep up the good work with the FlexDrives. At least those are designed well!

Bob

One question here:
Is it possible to DIY (like the LM317) a boost driver ?
Has anyone done this yet?

Yep it's possible, there was a thread a while ago before the forum switched from yabb that had all of the info for a (relatively) simple booster.. search will probably bring it up for you.