Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

How to Register on LPF | LPF Donations

Problem bucking a PL520

scumbagatheist

scumbagatheist

1
Joined
Feb 10, 2013
Messages
2,125
Points
63
Hi all. Without going into too much detail, let me explain what I need.

The PL520 has a Vf between 6 and 8VDC, depending on current. I have one of DTR's with the X-Boost set to 300mA.

The host I am using is built specifically for 2X26650 batteries, and I'd like to not throw off the balance w/ a one battery build.

I've tuned a Moh linear for the job to 305mA, but DTR tells me I am only going to get a usable 1 volt out of it to run on, if I can get it to regulate at all.

So, my question is this: Is there a buck driver that can handle the Vf of the diode @ ~8V while taking the 8.4VDC input and allow me to use this diode w/ the 2 X 3.7V batteries?

Thank you all in advance!

SBA
 





Keep in mind I'm not current (haha) on the latest generation of drivers, but it would seem that you need a Buck-Boost type driver. I know only of the old Flexdrive, and do not know if they are again available or if there is an alternative.

You're not going to find a Buck that only drops <400mV and if you did you would only have 400mV of battery charge before the diode loses power. You could find a LDO linear that drops <400mV (I know of several 5V fixed ones that only drop 160mV but there are variable types too) but again once you go below Vcc=8.4V-Vdrop you won't fully satisfy the Vf of the diode and it will start to crap out.
 
The problem with the Flexdrive is that its maximum Vin is only 5.5V. So, that wouldn't be appropriate for the desired setup.
 
scumbagatheist said:
The problem with the Flexdrive is that its maximum Vin is only 5.5V. So, that wouldn't be appropriate for the desired setup.
Click to expand...

Yes but it is also a boost driver. Unfortunately, the Flex V5 only boosts to 5.5V.
The MicroBoost is a better option.
Input V is 5.8V max so you cannot use 2 LiIons unless a diode is put in series with the driver but it will get your desired output V from one battery.

From the manual: A good rule of thumb to follow for input/output conversion is:
(Vout (Volts) * Iout (Amps) ) / Vin (Volts) < 1.2

According to this, the MicroBoost should be able to handle the diode with a single 4.2V LiIon.

8V x 0.3A / 4.2V = 0.571 < 1.2

http://hacylon.case.edu/ebay/laser_diode/Micro Boost Drive V1 manual.pdf

You should contact Lazeerer. I don't know if he has any X-boosts in stock but his drivers are really good.
EDIT: Just re-read and saw you already have an X-boost. Why not just pick a more practical host?
Alternatively, you could use the boost driver and one 26650 with one spacer.

IMO it seems silly to use a buck driver for a diode with such a high forward voltage. Boost seems much more practical unless you want a ton of batteries in series.
Also, why such a large host for a diode that only outputs 100mW of green?
It doesn't need much heatsinking. 2x26650s seems like overkill... I guess you want to be able to run it for days continuously...
 
Last edited:
Why not make a dummy (fake) battery and you are set?
 
Last edited:
You're missing the point. I have an X-Boost on it already. I WANT to use the 2 X 26650s that the host is designed for. That's why I want to buck this diode down to ~300mA.

What diode would I need to add in series to run two batteries?

norbyx said:
Why not make a dummy (fake) battery and you are set?
Click to expand...

I would really LOVE the run times that I'd get with two 4000mAh batteries!

The reason I am using the host I am is because it is a truly stunning host, and it's never been built with a PL520. The host is overkill for cooling, yes. But the cool factor of the build is worth the trouble.

I could use a slug if need be. But, like I said, I would love the killer capacity of the 2 batteries.

It's a one of a kind. It's worth some extra work.


RA_pierce said:
Yes but it is also a boost driver. Unfortunately, the Flex V5 only boosts to 5.5V.
The MicroBoost is a better option.
Input V is 5.8V max so you cannot use 2 LiIons unless a diode is put in series with the driver but it will get your desired output V from one battery.

From the manual: A good rule of thumb to follow for input/output conversion is:
(Vout (Volts) * Iout (Amps) ) / Vin (Volts) < 1.2

According to this, the MicroBoost should be able to handle the diode with a single 4.2V LiIon.

8V x 0.3A / 4.2V = 0.571 < 1.2

http://hacylon.case.edu/ebay/laser_diode/Micro Boost Drive V1 manual.pdf

You should contact Lazeerer. I don't know if he has any X-boosts in stock but his drivers are really good.
EDIT: Just re-read and saw you already have an X-boost. Why not just pick a more practical host?
Alternatively, you could use the boost driver and one 26650 with one spacer.

IMO it seems silly to use a buck driver for a diode with such a high forward voltage. Boost seems much more practical unless you want a ton of batteries in series.
Also, why such a large host for a diode that only outputs 100mW of green?
It doesn't need much heatsinking. 2x26650s seems like overkill... I guess you want to be able to run it for days continuously...
Click to expand...
 
Last edited by a moderator:
I guess you could use a 3.1V zener diode on the input of the x-boost. Just be sure to reverse bias the zener. That will drop it down to 5.3V max from 2 series Li-Ions.
 
Sigurthr said:
I guess you could use a 3.1V zener diode on the input of the x-boost. Just be sure to reverse bias the zener. That will drop it down to 5.3V max from 2 series Li-Ions.
Click to expand...

That's not very helpful when you consider his original goal: utilize two cells for longer run-times. Dumping most of the second cell's energy into a zener sorta defeats the purpose.
 
Cyparagon said:
That's not very helpful when you consider his original goal: utilize two cells for longer run-times. Dumping most of the second cell's energy into a zener sorta defeats the purpose.
Click to expand...

Not to mention it is another item that will be producing a lot of heat that has to be managed.
 
If you're stuck with a 2 cell host and you can't find a driver which meets your I/O reqs there isn't a whole lot more you can do. I didn't say it was a great idea, lol. I'm not up to date on the current driver market, but a quick search doesn't pull anything up either.
 
Thanks Sig, I'm afraid that's where I ran into trouble as well. Maybe the FMT will work, I have to check the specs again.

I'll leave this thread up in case some genius on the forum will come to the rescue.
 
What about the Buckboost? It's Vout is 2.5-.85*Vin. So, that comes to just over 7V...Has anyone tried this combination yet?
 
You must log in or register to reply here.


Back
Top