The SimpleDrive2 - Very easy to set! Now with a feeler!

HIMNL9 · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver.

Right, just remember that it may give you a little bit less of half the wattage (cause the heat don't dissipate too good from the packed sides), but that can work, yes ..... only, the normal small SMD resistors usually have low powers .....

Standard powers are, usually:

0805 size (2x1.3mm) = 1/10W

1206 size (3x1.5mm) = 1/8W

1210 (3.2x2.6mm) and 2010 (5x2.6mm) sizes = 1/4W

2512 size (6.3x3.1mm) = 1/2W

There are also bigger ones, but then you need a lot of space and the driver become bigger ..... a possible solution for high currents can be "pack" sandwich style 3 or 4 or more resistors (calculating one more for the safety, about the power), and then mount them as a single unit, also side-mounted, if the height of the assembly become larger than a single resistor.

Johnyz · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver.

Actually, according to their specs, my 1210's are 0.5W and the 2512 is 1.3W.

Wolfman29 · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver.

Got a 3216mm SMD, 2W resistor

jib77 · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver.

2512 can be had in 2W. That's what I use.

Jufran88 · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver.

HIMNL9 said:
Use a configuration like this one for the current setting resistors:

You cannot adjust the current from min to max value in a single step, but with this system, you can still made a driver that can be adjusted for a certain range (assuming you always keep the power in the pot tree at the maximum that the trimmer can manage, you need to calculate the values)

This looks like it would work wouldn't it? The Rset in parallel with the current limiting resister and pot would increase its ability to dissipate the extra power since the wattage would add up.

HIMNL9 · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

Uhm, maybe some company made SMD resistors in different powers, for these sizes, i posted the standard powers ..... anyway, check well them, before use

@Jufran88: yes, this system limit the excursion of the current that you can regulate, but at the same time it permit you to use a more "normal" 1/2W trimmers (the 3.3 ohm value is for 500mW trimmers, for 250mW ones you need to use at least 5.6 ohm, but the regulation is reduced) ..... you need to choose the RSET for the value of current that you need, calculating it with half of the value of the trimmer in parallel indicatively), so you can regulate the current a bit more or a bit less of the middle value you need.

As example (all values rounded to 2 decimals only):

supposing you want a current of 500mA, and have a trimmer of 1/2W 50 ohm, then you must keep the power dissipated from the trimmer at maximum 500mW, this mean a 3 to 3.3 ohm resistor in serie to the trimmer (not less than 3 ohm), say you use 3.3 ohm cause it's a more "standard" value ..... this means you can go, with the trimmer branch only, from 1.25/53.8=23mA to 1.25/3.3=378mA, if you add another 3.3 ohm as RSET, your resistance go from 3.11ohm (53.8 in parallel with 3.3) to 1.65ohm (3.3 in parallel with 3.3), so your current can be regulated from a minimum of 1.25/3.11=401mA, to a maximum of 757mA, without burn out your 500mW trimmer (if instead you use only the trimmer, at 757mA it need to dissipate 1.25*0.757=946mA, and it will probably start to smoke before reach this point.

For 250mW trimmers, instead, the regulation range is reduced ..... using a 250mW trimmer with a 5.6ohm resistor in serie, you can go, with the trimmer branch alone, from 22 to 223mA (it's already at the limit, it gives you 280mW at 223mA), and adding a 3.3 ohm in parallel you can regulate from 3.11 to 2.07 ohm, that gives you a range from 400 to 603mA (still in the range of the 500mA, but reduced regulation capability)

Increasing the currents, these ranges will become reduced more than so.

rhd · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

Sadly - you still need a test load - because your cells might not be able to supply the current level you've selected - you'd want to know

Johnyz · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

Yep - but for basic quick setup it would be enough. There are other drivers if people want to push their diodes to the edge. I'm not targeting the top enthusiast laserists, you know.

rhd · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

Lol - understood.

Having said that, if you actually get this PCB made (the D2Pack version for 1086), I'd happy buy a bunch of blanks from you, and add my own 1085 + resistors

Jufran88 · Mar 24, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

HIMNL9 said:
Uhm, maybe some company made SMD resistors in different powers, for these sizes, i posted the standard powers ..... anyway, check well them, before use

@Jufran88: yes, this system limit the excursion of the current that you can regulate, but at the same time it permit you to use a more "normal" 1/2W trimmers (the 3.3 ohm value is for 500mW trimmers, for 250mW ones you need to use at least 5.6 ohm, but the regulation is reduced) ..... you need to choose the RSET for the value of current that you need, calculating it with half of the value of the trimmer in parallel indicatively), so you can regulate the current a bit more or a bit less of the middle value you need.

As example (all values rounded to 2 decimals only):

supposing you want a current of 500mA, and have a trimmer of 1/2W 50 ohm, then you must keep the power dissipated from the trimmer at maximum 500mW, this mean a 3 to 3.3 ohm resistor in serie to the trimmer (not less than 3 ohm), say you use 3.3 ohm cause it's a more "standard" value ..... this means you can go, with the trimmer branch only, from 1.25/53.8=23mA to 1.25/3.3=378mA, if you add another 3.3 ohm as RSET, your resistance go from 3.11ohm (53.8 in parallel with 3.3) to 1.65ohm (3.3 in parallel with 3.3), so your current can be regulated from a minimum of 1.25/3.11=401mA, to a maximum of 757mA, without burn out your 500mW trimmer (if instead you use only the trimmer, at 757mA it need to dissipate 1.25*0.757=946mA, and it will probably start to smoke before reach this point.

For 250mW trimmers, instead, the regulation range is reduced ..... using a 250mW trimmer with a 5.6ohm resistor in serie, you can go, with the trimmer branch alone, from 22 to 223mA (it's already at the limit, it gives you 280mW at 223mA), and adding a 3.3 ohm in parallel you can regulate from 3.11 to 2.07 ohm, that gives you a range from 400 to 603mA (still in the range of the 500mA, but reduced regulation capability)

Increasing the currents, these ranges will become reduced more than so.

Ah, ok so for example if I wanted to go for higher outputs:

Rset = 2 Ω .5W
Rcl = 1 Ω .5W
pot = 100 Ω .5W

R1 = 101 Ω
R2 = Rset = 2 Ω

so Rt = 1/(1/R1)+ (1/R2)
= 1/(1/101) + (1/2) = 1.96 Ω

and V = IR
1.25 =I(1.96)
V = 1.25/1.96
= .637A or 637 mA

637 mA would be the starting current when the pot is 0 and max out at the current limiting resistor (1.25A).

So since P = Isquared *R and power adds in parallel

Pmin = (.637A)^2(1.96)
= .795W of power dissipated by the parallel array

Pmax = (1.25A)^2(1.96)
= 3.06W needs to be dissipated

So I'm guessing it wouldn't be efficient at higher outputs

, but the those resistors in parallel (current limiting resistor with trimmer in parallel with Rset) could dissipate up to 1 watts?

I 'm guessing the best solution for this driver to keep cost down and the circuit simple is to just leave the resistor pads open and let builders decided how much current they want to run and just calculate it by ohms law and solder it themselves.

HIMNL9 · Mar 25, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

Well, the intention in designing that configuration was to not fry the trimmer when it reach its lower value, and for this reason, you can't change the resistor in serie with the trimmer freely ..... if you use a 0.5W trimmer, the resistor in serie must not be less than 3 Ohm (3.3 Ohm gives you 470mW, 3 ohm gives you 520mW)

So you need to made your calculations keeping these values, for the trimmer part.

In your example, with a RSET of 2 Ohm (and a resistor of 3 Ohm in serie with a 100 Ohm 0.5W trimmer), you can go from 637mA to 1040mA, and you need a RSET that can hold at least 780mW.

Anyway, keep in mind that the regulation is not linear ..... i mean, turning the trimmer the same number of degrees each time, it regulate less when it's in the maximum value range, and regulate more when it's near its minimum value range ..... this can be solved, partially, using a logarithmic trimmer, instead of a linear one.

123splat · Mar 25, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

I don't want to throw you guys off the direction in which you are going (series parallel resistor and power calcs, and all that), But, if I may,
Not much attention was given to RHD's comment about still needing a test load and the title of the thread suggest (?) that one would not be needed. I'm admittedly a neewbee at lasers, but I've been playing with electrons a LONG time, not done much work with surface mount dev.s, but through hole carbon resistors have lousey tollerances and,,, Are you really suggesting to the new guys (your targeted audience) that with this driver, they can solder a couple of resistors in, or make some pad jumpers, hook up thier diodes and go? Not questioning your knowledge or capabilities, but as a new guy, it kinda makes me nervous to suggest that the currents not be checked before trying to light up a diode (without the smoke, of course).
Don't kill me yet. I'm old and feeble and just asking a question.

rhd · Mar 25, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

Thank you ^

For one, this thread has gone back down the path of looking at including pots/trimmers. In that case, I've no idea how you could avoid a test load.

Even in the multiple selectable resistors config, you're talking about such low resistances, that I would have to think poor soldering jobs could start adding meaningful resistances to skew output current.

Regardless - I don't think there is really any driver design that does away with the need for a test load...

Johnyz · Mar 25, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

You know, unless the resistor is faulty, a bad soldering job can only cause lower currents... Anyway, since assembly service almost never does a faulty soldering job, I still think for the basic use you can do without it. Also, we could do a driver that uses the photodiode present in many red or IR diodes, that adjusts to always deliver the current we want. hmmm...

rhd · Mar 25, 2011

Re: The SimpleDrive2 - New budget driver. No more test loads or multimeters!

I think the goal of eliminating test loads is requiring far more complexity than it mitigates.

Think about this -
Olike, Aixiz, etc sell fixed 1A drivers for 445, with absolutely no setting of anything required. Yet still, nobody would wire one to a diode without testing the actual current first.

So why would that be any less true of what gets created here?

I'm totally in support of this "grassroots" driver design. I just think it would be more responsible to take the comment about not needing test loads out of the title.

HIMNL9 · Mar 25, 2011

Re: The SimpleDrive2 - Very easy to set!

Sorry for the previous thread derailing :beer:

No intentions to bash rhd work, nor any other user work ..... it was just a suggestion about how add a trimmer without fry it, and discussion "took the hand"

The SimpleDrive2 - Very easy to set! Now with a feeler!

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