I really don't understand the need for drivers

Hi everyone.

I recently got my PHR-803T Sled and extracted the laser out of it. At the moment its secure in the aixiz module.

However I really don't understand the need for a whole circuit to drive the laser. Surely if a resistor was used to limit the current to a certain level, then the laser diode wouldn't be damaged. So why can't a resistor be used instead of a whole driver circuit.

- Yosheli

You can. But it's not a good idea. Resistors do work to limit current, but they're dependent on battery voltage to maintain said current. If you have a battery with a higher than normal voltage, you will be running the diode at a higher current. On the other end as the battery is used, voltage drops and so does your current.

Resistors also don't protect against ESD or voltage spikes and transients caused by things like switches.

because a driver is meant to be a current regulator, this means it will keep the diode current ALWAYS the same. by limiting it with aresitors you will get the desired current for a moment, asthe battery voltage will go down and down. Also, batteries cannot provide a 100% stable current

The CC driver provides stability to your LD and your sanity. Whats been said above is good reason to get a CC driver.

Mike

A resistor doesn't prevent thermal-runaway.

Yosheli said:

Hi everyone.

I recently got my PHR-803T Sled and extracted the laser out of it. At the moment its secure in the aixiz module.

However I really don't understand the need for a whole circuit to drive the laser. Surely if a resistor was used to limit the current to a certain level, then the laser diode wouldn't be damaged. So why can't a resistor be used instead of a whole driver circuit.

- Yosheli

Click to expand...

Welcome to the Forum....

I can tell by your question... that you have done no research on this
Forum before asking this old noobie question....

Had you done a little reading you would have known what the other
members have already explained...

As a new member...you could start here.....

http://laserpointerforums.com/laser_pointer_forums_3/forum/forumdisplay.php?f=36



Jerry

Really, the best way to prove the need for drivers to someone in doubt is to let them see what happens if they don't use them. After they blow enough diodes they will either decide that using a driver might be wise, or they will get pissed off and stop trying to build lasers.

also you need to worry about voltage spikes. so you would need a voltage regulator also.

as posted above, the driver not only provides the constant current to power the diode, but reverse polarity protection (cross the wrong wires), and protects against spikes with a capacitor. IT IS REQUIRED.

FireMyLaser said:

A resistor doesn't prevent thermal-runaway.

Click to expand...

Thats a major problem indeed even when working from a stable power supply: the laser diodes drop voltage lowers with increasing temperature, and limiting a fixed voltage using only a resistor creates the undisired effect of running even more current when its getting hot.

If you don't believe us, try it out for yourself, then report back and tell us what happens. Then read the FAQ's.

-Mark

I really dont understand the need for drivers

hate to say it, but I read the title as "Good place for dead on front picture"

Now, Im not one to judge, but I dont think we should have dead on the websites front picture. Doesnt really support what the site is about.

Now that this has been started could someone direct me to where i could learn how to set a rkcstr micro-drive laser driver to 100mA?

Unlike what others are saying:

NO, you absolutely don't "need" a driver to run your laser diode. You just need a battery, a resistor (preferably adjustable), a multimeter for measuring the current, and the diode. Hook them all up in series, turn the resistor down starting with the highest value, and observe the multimeter until you get your desired current.

In fact, I'd say if you can't handle this (you do need some [trivial] calculations for getting a good resistance range), then you shouldn't bother adding money to buy drivers. The LM317 type linear drivers are rather simple and forgiving, a DrLava Flexdrive however needs to be treated just right.

In the end, a laser diode is a diode is a diode, no need to break into a sweat when handling them. (Actually DX sells LED flashlights that don't even have a resistor - but that works only because the voltage drop over the LEDs is just a bit below the voltage of a RCR123 battery; the internal resistance does the current limiting).

What can go wrong if you use just a pot instead of a driver? Simple, you can set the pot to the wrong value (turn resistance down too low = current too high). Exactly the same thing can happen with a driver. With a driver, however, there's a couple of other things that can go wrong (like too high input voltage, operating them under open circuit conditions, connecting them up wrong, output cap charged to too high a voltage).

What will happen with a simple resistor is, as you drain your battery, its output voltage will drop, so will the current and the output power from the laser, unless you monitor this with your multimeter and keep adjusting the resistor. A driver compensates for this drop (within limits) so it's a bit like a "cruise control". The above-mentioned FlexDrive will also transform voltages so you can run a 5V bluray diode off a 3V battery.

Because the current is inversely proportional to the resistance, I recommend using a logarithmic pot; otherwise it may get pretty sensitive in the high-current range.

And oh yes: I have done this. When I got my first LDs and FlexDrivers, the FDs were the most expensive and sensitive parts, so I decided to try the LDs first (I didn't want to kill the FD by connecting it to a broken LD): hook the LD up with a series resistor to a variable lab power supply and the turn up the voltage carefully until I got light...

Many people speak with conviction only because they never dream of questioning the assumptions.

@dr.ebert---if a guy is asking how to set a pre made driver, how on earth is he gonna be able to follow your adivice? pre made drivers can be bought from numerous places. and super inexpensive ones can now be bought from o-like for about less than 10 bucks a pair.

edit* i just found the link. and it is less than 8 bucks shipped

2pcs CC power supply driver£­>Laser Accessories£­>Laser&lighting products£­>www.0-like.com

Momo66342 said:

Now that this has been started could someone direct me to where i could learn how to set a rkcstr micro-drive laser driver to 100mA?

Click to expand...

READ HERE
http://laserpointerforums.com/f39/micro-drive-laser-driver-rkcstr-22553.html