direct drive vs regulated

[vincenthooi]

okay.. noob question here.

how much power does direct driven 445nm with a 18650 battery puts out?

will a lm317 driver set to a specific miliamp outshine a 18650 battery direct driven 445nm diode?

 

[Kevlar]

A quick search for "direct drive" netted this thread: http://laserpointerforums.com/f65/direct-drive-445-host-52918.html as my first result.

Always try the search function my friend, almost any question you can come up with regarding lasers has already been answered. :beer:


EDIT: Here is another: http://laserpointerforums.com/f52/445-nm-build-review-51714.html

 

[LSRFAQ]

Direct drive only works if the battery has a high internal resistance, and self limits the current flow. Pick the wrong battery, and boom! Buy a proper current limiting driver and you will be better off.

Steve

 

[LarryDFW]

Direct drive only works if the battery has a high internal resistance, and self limits the current flow. Pick the wrong battery, and boom! Buy a proper current limiting driver and you will be better off.
Steve

Since I built the "Direct Drive 445nm" referenced above,
I need to correct this erroneous information.

The "Direct Drive 445nm" I built, uses a "Low IR" LG 18650 battery.

It works because the 4.2VDC battery voltage,
matches up very well with the 445nm diode voltage requirement @ 600ma current draw.

The diode must be heatsinked properly, to stabilize the diode temperature.

If the diode got too hot, the current would increase,
due to the voltage across the diode decreasing.

It is the most efficient driving possible,
and will give the longest operating time for a given battery capacity.

It has been working fine for several months now.

LarryDFW

 

[vincenthooi]

i guess i asked the question the wrong way.. sorry
what i meant was.. is a laser with a driver more powerful than a laser without driver?(output), not counting efficiency

 

[Flaminpyro]

Larry when you say working fine for several months now do you mean with out recharging the cell form it's original charge :thinking:
if not then how many hours of on time do you figure it gets between charges ?

Since I built the "Direct Drive 445nm" referenced above,

It has been working fine for several months now.

LarryDFW

@ vince Yes a driver can boost the voltage higher than the battery voltage in this case which will give the diode more power but it will be at the expense of draining the battery faster with a higher current draw.

 

[LarryDFW]

Larry . . . then how many hours of on time do you figure it gets between charges ?

I have only operated ~2 hours between charging (laser was still working).

I do use a new high capacity type of #18650 that allows charging to 4.35 VDC.

Larry DFW

 

[AUTO XX]

vincenthooi, Larry DFW's project is the exception, not the rule.
Most times, if you direct drive a diode it will be VERY powerful but only last about 1/2 of a second.
LDs get into whats called "thermal runaway", basically the diode draws current, internal temp goes up, diode is able to draw more current, internal temp goes way up, pieces melt.
Laser Drivers are supposed to regulate current, supply the necesary voltage, and filter any spikes from the power supply.
Good laser drivers will get you nearly unlimited working time on a good, high quality, properly heatsinked, non-overdriven Laser Diode (LD).
Short answer: direct drive kills diodes

 

[LarryDFW]

The important concept, is that you want to limit current thru the laser diode.

That can be direct drive, a suitable power resistor, linear current source, or a switching power supply.

A variable power supply will allow you to determine the voltage required for the current desired.

Then you can design the circuit to deliver the required voltage to deliver the current level chosen.

LarryDFW

 

[AUTO XX]

I guess technically you can make a laser more powerful with a driver because it will give you the maximum current the diode will handle as opposed to running it at whatever your batter (low resistance) can supply.
An aw battery, 18650 for good capacity, a driver (dr lava has very good quality drivers) and you should get the most out of your laser.
If you want to push it over 1.5A, you should get 2 drivers and wire them parallel with both driver's range/pots set to add up to your required current.
Might have said that poorly but its late, I just got laid, and my mind isn't completely clear right now ^_^