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

[Johnyz]

Re: The SimpleDrive2 - Very easy to set!

Okay, you got me. Yet I would still say this is the first non-fixed driver you could, if in a hurry, wire a diode and power it up. Also, +3.6V and -3.6V = 7.2V right?

 

[rhd]

Re: The SimpleDrive2 - Very easy to set!

Johnyz: By that logic, it's not the first. In fact all of Dr. Lava's drivers meet that same criteria.

IE, you could set their pots to the lowest current setting, and then use the solder bridges (as used here) to set the current. You would "know" (by the definition used in this thread) what current you were getting, because it would be the low bound of the current range set by the solder bridge. Same could be said for setting the pot at its highest, and similarly relying on the solder bridge's upper bound.

It's still not a good idea, and nobody would ever sell a Flexdrive, Microboost, etc, with that advice. It's no more wise to do so with this driver. Perhaps even less wise, given that it is targeting new entrants / beginners who are at least as likely, if not more, to have done something wrong that would have otherwise been caught by a test load.

Again, fully support this endeavor, just think it shouldn't be provided with the guidance that a test load could be avoided "in a pinch" etc.

 

[Johnyz]

Re: The SimpleDrive2 - Very easy to set!

You bashed me to it. Unless I find an easy buck-boost way, I think I'll not develop a buck-boost version, since the OdicForce one looks great and cheap enough.

 

[Jufran88]

Re: The SimpleDrive2 - Very easy to set!

@HIMNL9:
Sorry, I'm really a novice at this, but if you had a 2W rated resistor in series with the trimmer and RSET was 2W rated would it allow it to dissipate more heat together? Or it just depends on individual resistor watt rating?

@123splat, Johnnyz, rhd:
I agree I don't think anyone would be able to eliminate the test load. It's always a good thing to double check the output before connecting it to a LD.

 

[123splat]

Re: The SimpleDrive2 - Very easy to set!

Johnyz, NO intent to bash! I think your idea is great and look forward to developement/deployment. I am just nervous about the no test load issue (I've wasted a few diodes by stupidity/ignorance).

 

[anselm]

Re: The SimpleDrive2 - Very easy to set!

About the test load issue:
Linear drivers, like this one is going to be, will always put out the same current, no
matter what load (Vf) is attached, as long as the input voltage is enough for
the diode's Vf + the drivers dropout.

So you could actually get away without a test load by simply putting your DMM in
current measuring mode and using it directly on the drivers output.
Right?

Now, switching drivers (boost/buck) are a different animal altogether, and you
MUST accurately simulate the diodes Vf to get an accurate reading...

 

[Johnyz]

Re: The SimpleDrive2 - Very easy to set!

This is getting interesting... hopefully, I'll finish the prototypes soon.

 

[Wolfman29]

Re: The SimpleDrive2 - Very easy to set!

Aye. my PCBs will be developed soon (I am using a slightly different mechanism for my LM1117 driver), and then I will post them here too.

 

[HIMNL9]

Re: The SimpleDrive2 - Very easy to set!

@HIMNL9:
Sorry, I'm really a novice at this, but if you had a 2W rated resistor in series with the trimmer and RSET was 2W rated would it allow it to dissipate more heat together? Or it just depends on individual resistor watt rating?

It's matter of current, and the current flowing in elements connected in serie is always the same, where for elements connected in parallel it change with their values ..... and also, the voltage of the elements in parallel is the same, so the powers are different in the two branches, depending from the current that flow in them (P=V*I, common Ohm laws) ..... so, the purpose is to keep the maximum current that flow in the trimmer branch, at a level that, for 1.25V, it does not cause a power dissipation greater than the one that the trimmer can hold, and let the rest of the current flowing through the fixed RSET ..... so, for a 500mW trimmer, this is done using a serie resistor of 3 ohm, that keep the current in this branch at a maximum of 1.25/3=417mA, causing a maximum power dissipation of 520mW (the trimmer can hold easily 20mW extra power), and this in the trimmer branch is the variable part of the current ..... where the fixed value RSET determine the rest of the current, that is a fixed value, and can be greater than the one in the trimmer branch, ofcourse, and when this happens, also the power dissipation is greater on the RSET, that must be dimensioned opportunely. (sorry, can be explained better, i think, but English is not my main language)


EDIT:

@anselm, remember about power dissipations, too .....

For a linear driver, all the unused power will become dissipated in heat from the regulator .... if you use a test load that take part of this power (causing a dropout and simulating the LD FV), the regulator under test will need to dissipate less power ..... just as example:

Assuming you are testing the current on an 1A driver for a 445nm diode, that have a FV of 4.5V, powered from a 9V input voltage ..... if you use a test load that emulate your LD FV, it take and dissipate 4.5W, and the driver need to dissipate the remaining 4.5W ..... if you connect your DMM directly on the output of the driver, and your DMM internal resistance cause, say, 0.1V dropout, your driver need to dissipate the remaining 8.9W, and maybe it fry or give you false readings going in thermal protection shutdown .....

 

[Wolfman29]

Re: The SimpleDrive2 - Very easy to set!

Great! So my board will be produced soon. Also, I am making the whole bottom of the board copper in order to make it perfect for heat sinking!

 

[rhd]

Re: The SimpleDrive2 - Very easy to set!

Anselm:
I'm not sure thats a great idea either.
With nothing actually consuming power (likea diode or test load) where does that extra power get dissipated? Probably the IC. Basically, you could leave the IC to dissipate 8V as heat. I think that could toast it pretty quickly.

 

[rhd]

Re: The SimpleDrive2 - Very easy to set!

I was beaten to the point

 

[123splat]

Re: The SimpleDrive2 - Very easy to set!

I could be wrong, BUT,,, in my experience, an unloaded (no RL in the output) the LM317 does not conduct in current or voltage regulator configurations. With no load, the only current draw is in the reference (adjust) loop and that is down in the 100uA range in volts mode. You don't have power dissapation until the load starts drawing current. The LM317 is not a true shunt regulator (like a Zener and a resistor to ground). If you have a very leaky cap on the backend, this presents a load, but otherwise, no load, the regulator stays cool.

 

[rhd]

Re: The SimpleDrive2 - Very easy to set!

Except that as soon as you put your DMM on the output, expecting to measure current, the current will have to flow for it to measurable (obviously). The full current MUST come from the batteries, and thus the full voltage of that battery (or two or three) needs to go somewhere too. With only a DMM in the circuit to dissipate heat (and it won't dissipate very much at all), the entire 8V (for 2 cell setups) or 12 V (for 3 cell setups) is left to the IC to dissipate.

A linear IC can't turn Voltage into current. So if your driver is set to output 1.5A, and if you expect your DMM to be able to measure this without a test-load, you have to also expect that the batteries will be SUPPLYING that 1.5A. Since they'll be supplying that 1.5A at either 8V, or 12V (probably), you're looking at 12 to 18 Watts of heat being dissipated by the IC (minus a little bit that is dissipated by the resistor, and an even littler bit dissipated by the DMM).

But in other words - way too much for the IC to handle, even very briefly.

 

[Johnyz]

Re: The SimpleDrive2 - Very easy to set!

Woah, that's a very interesting technical conversation I started - if I get the driver manufactured and sold, this would be an ultimate success! Also, I just uploaded some new pictures of the SOT223 version.

 

[anselm]

Re: The SimpleDrive2 - Very easy to set!

Yes I get your point. But:
When I check for output in a linear driver, I already know what current to expect
from the resistors used on the adj-pin. I don't have to leave the setup running for a minute
to read the display. I power the circuit, take the reading and turn it off. 3-4 seconds have passed.
If you are planning on using high currents over 1A, you have to heatsink the driver anyway
for any appreciable runtime later on in the final build.

Of course if a potentiometer is involved, it's not very practical to turn it off between every
tweak.

Yes, it is always recommended to use a testload.
When I was building my PSU labby with a LM317 generously heatsinked, I was curious
and tried both methods, with and without testload. I got the same readings
both times. The IC didn't go POOF either.

So, if you are not totally oblivious to what you are doing, you can get away
without a testload on a linear driver. But it is a moot point because a testload is about
the easiest to make and cheapest to obtain things ever in this hobby, so you don't have
an excuse not to have one, if your are building.

Sometimes I just can't be bothered to use it.