Common test loads and 445 diodes

[Morgan]

Hi All,

What exactly is the issue with 445nm diodes and common test loads using the 1N4001, (I think that's the number), diodes?

I know we're trying to put a lot of current through them but I'm curious that, when using a microboost, it's suggested to just use the Red setting instead of the Bluray one. Do I get the same current being supplied to my 445 diode if I set my driver to, say 800mA using the Red setting? If this is the case, can I just use the Red setting when using an 8x Bluray? If not why not and how far out will the actual current output be?

I don't fully understand buck/boost, or just boost, circuits so don't understand how they up convert, (except that it's to do with back EMF spikes from inductors etc), and what correlation output voltage has to output current, for a fixed input voltage and input current. Is it a simple power in = power out conversion?

Any enlightment welcome.

Thanks,

M

 

[Tabish]

Voltage drop on 1N4001 is 0.7V. So 6 of these in series with a 1ohm resistor will work for a 445 test load.

The 445nm diodes use about 4.4V at 1A.

(Power out) = (Power in) x (driver efficiency)

So 4.4V @ 1A = 4.4W (output power to diode)

4.4 = (Power in) x (0.8)

So the battery feeds 5.5W

 

[Benm]

Keep in mind that the max current for the 1n400x diodes is 1 amp, and they do get rather hot by then. If you need more, go for 1n540x - those can handle up to 3 amps.

 

[Bionic-Badger]

I never thought the dummy load really mattered with those bucking converters, since they adjust their output voltage as needed, and the current regulation is feedback regulated. The red vs violet dummy loads seem more appropriate for linear-regulator-based drivers, that may have a minimum input voltage.

I know that Dr. Lava's manual for the Flexdrive doesn't specifically say how many diodes to use for the dummy load. It might just be the minimum needed to drop the minimum voltage that the driver can produce. The "red" setting for the 445nm diode may be just to prevent the overall voltage drop from going too high because of the large currents. So for example, if you used a violet dummy load with six (6) rectifier diodes to drop 4.2V, and then powered your dummy load at 1.5A over a 1ohm resistance, that'd create an overall voltage drop that is beyond the 5.5V the driver can supply. Having four (4) rectifiers would only drop 2.8V, giving a reasonable amount of room at max current (2.8V + 1.5V = 4.3V).

 

[lasersbee]

That makes sense for the Flexdrive....
Then using that logic...a single High Wattage 1 Ohm or 0.1 Ohm
resistor could be used to adjust the current of a Flexdrive...


Jerry

 

[Morgan]

^ Yes, I get the logic for the Flexdrive hitting maximum output voltage at 1.5A. I think this may have been the reason for the development of the Microboost for the higher power BRs. Microboost drives shouldn't suffer with this so long as you are only hitting the 1A output currents using the 1N400X testload diodes, then your test load, although getting burning hot, (mine does anyway), will tolerate it.

I'm still not clear here though because people seem to be having problems at much lower outputs than 1.5A using the Microboost on the 445s. LDs flashing etc. I have noticed this; when using my bench PSU I have to make sure there is more than enough current, (at the correct voltage of course), to supply the Microboost. If not it goes into shutdown restricting voltage of the PSU to around 2V but will still supply a measurable 200mV or so across the dummy load resistor. Dr.Lava initially suggested this may be due to my PSU going into shutdown as it may see the initial charging cycle of the drivers caps as a short but I don't think this is the case after observing the same thing happening up to a certain threshold.

I've seen this debate regards the need to drop the correct number of volts, using a test load to accurately simulate a diode, before but it never seems to be definitively nailed as to the real absolute, 'necessity', of them. I totally get that it's best practice when learning and just starting out to use one but as Jerry says, you can probably drop enough volts to set correctly with just one resistor if the voltage drop is not critical?

I guess it boils down to this on a boost/buck driver - If I replace my red diode being driven at 400mA with a suitably capable BR, will it too be running at 400mA, (whilst remaining under the 5.5V max output), and vice-versa?

With a boost only driver - Assuming large enough battery capacity and current draw capabilities, if I replace my BR being driven at 400mA with a 445nm will it be driven at 400mA, and vice-versa?

As far as I know, linear drivers, provided with enough volts to maintain proper regulation, will supply any diode with the same current as before but adjust voltage accordingly.

I guess just doing some tests using test loads and a high wattage resistor would be appropriate as I feel I am speculating which isn't that productive. Any more ideas to at least make some testing safer if I wanted to do this and not destroy a perfectly useable driver?

Thanks,

M

 

[BShanahan14rulz]

I'm still not clear here though because people seem to be having problems at much lower outputs than 1.5A using the Microboost on the 445s. LDs flashing etc. I have noticed this; when using my bench PSU I have to make sure there is more than enough current, (at the correct voltage of course), to supply the Microboost.

So it still does this even if the supply is more than capable of supplying the needed current? I figured the reports were of users trying to discharge LiCo too quickly.

I'm planning on using the Microboost in my build in the future, and would definitely appreciate any information that you uncover in your probing of the Microboost. Heck, I might even need to get some IMR cells just for this blue laser, assuming I ever decide whether to make it semi-portable or not.

 

[Morgan]

I think the concensus was that it was due to battery discharge but I didn't know if the drivers were set using the same batteries and problems encountered only after the LD was installed, or if the drivers were set using a PSU and then LD and battery setup showed the anomaly. Those who experienced those issues will better be able to tell us here.

M

 

[Bionic-Badger]

That makes sense for the Flexdrive....
Then using that logic...a single High Wattage 1 Ohm or 0.1 Ohm
resistor could be used to adjust the current of a Flexdrive...

Well, from the manual, the Flexdrive's output voltage is between 2V and 5.5V, so you'd need at least one rectifier in series at 1.5A. Probably the best is to just use three (3) rectifiers for all test loads so you never dip below the minimum voltage.

 

[lasersbee]

I actually have never used a FlexDrive or MicroBoost drive...
I should perhaps get some and do some tests myself...
I have used some other non Laser Boost Drivers...

Jerry

 

[Bionic-Badger]

I'm not really sure why people are using the Microboost drive for their 445nm lasers when it can only provide up to 1A. Sure, it's good for when you need up to 13V, but the Flexdrive seems like a much more appropriate driver as it can power up to 1.5A. They're even the same size and price.

 

[Morgan]

^ I totally agree here. I did use a Microboost on my first 445 diode but only because I had bought the driver for an 8x BR build and had nothing else. As the Flexdrive is more efficient too I will be using them for 445s of the future.

It has to be said that the pot on the Microboost is nicer to use but the range selection is more tricky IMO. Both the SMD resistors came off the last Microboost I set and I only just managed to resolder them. Maybe it's because I'm not right handed. Any chance of producing a Left Handed Microboost Dr.Lava?!!! :crackup:

M

 

[BShanahan14rulz]

There are a few things that benefit the BoostDrive: It can be TTL modulated, it also can be switched on and off with a low current tactile switch. It has a sturdier potentiometer that allows for more adjustment cycles (the FlexDrive potentiometer is rated for about 15 adjustments max.) Also it's a little more stable when it gets hot.
If you are on the border, I'd suggest going with the MicroBoost for these reasons. Morgan is right about the original reason for the MicroBoost.

http://laserpointerforums.com/f67/m...-18650-driving-445nm-ld-52913.html#post740223

If someone can find a way to easily integrate the 3, 5, etc. mode flashlight "drivers" (glorified PWMs) with the TTL modulation, would be neat. Also the ability to use with a tactile switch (though I'll be using a clicky or high-current momentary push button) would be neat for those making pointer-style builds.

 

[Benm]

That makes sense for the Flexdrive....
Then using that logic...a single High Wattage 1 Ohm or 0.1 Ohm
resistor could be used to adjust the current of a Flexdrive...

I suppose the logic is that you want to create a dummy load that behaves like a laser diode does electrically. With pulsed drivers, for example, i replace the 1n400x diodes with fast-recovery diodes, so that they are fast enough to follow the pulsing.

When working with DC, a couple of rectifier diodes in series with a small resistor resemble a laser diode rather well.

Dummy loads are for checking wiring errors in drivers and such though. A well designed and properly constructed current source wouldn't care what its load is, as long as it can supply enough voltage.

I work with linear current sources mostly, and to those it doest matter at all - laser diode, 1 ohm resistor, monkey wrench with crocodile clips attached... it supplies them all with the same current, but your voltage may vary

 

[kiwi]

Bottom line is?
I've been reading a lot of different recommendations from different people, in many threads. Some say 4 diodes + 1ohm, others say 6 diodes + 0,1ohm.

 

[kiwi]

Anyway, i made a test load out of four diodes 1N5404 (max 3A) and a 1ohm 5W resistor. And a 10kohm resistor betwen anode and kathode to discharge the capacitor in the flexdrive.

Here's a pic while tuning the flex drive for the 445nm LD. DMM at the bottom is showing millivolts over the resistor (convertable straight to milliamps). 4.19 is the voltage supplied from the PSU.