Reading spec sheets (meanwell LDD-700LW)

I'm making no sense of your reply there. In case it's not clear, my point is that the quoted spec has no real meaning. Making guesses as to what they might have meant is not engineering and should not be done with anything. I wouldn't even be happy to do it with gimmick products.

NT

Reply to
tabbypurr
Loading thread data ...

Go ask your wife what you should do next.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

Did you actually read the datasheet? It's pretty clear once you realize that the "levels" are just digital levels, high and low. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

I don't get what you are saying. The data sheet is clear. A valid low is below 0.5 volts and a valid high is between 3.5 and 8 volts. The fact that they don't indicate the low should not be appreciably below ground doesn't mean the limit on the upper voltage is not valid. I'm sure they pointed this out to warn a user to not use a pullup or drive from the LED power source which can be much higher than 8 volts.

--
Rick C 

Viewed the eclipse at Wintercrest Farms, 
 Click to see the full signature
Reply to
rickman

What is hard to understand about this...

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

Datasheets d If you want a logic 0 it has to be = 3.5V If you don't want to burn it up, it has to be < 8V

So if it's between 0.5 and 3.5 volts it is not predictable with certainty. Datasheets are about what you need to know to design something that you can be certain about. They don't say maybe anything.

Now the other issue is that you might not understand PWM. The brightness is proportional to the duty cycle, which is the percentage of time the input is a logic 1. We don't know the frequency because you didn't quote that spec but I would guess a few KHz. It would probably work over a wide range but the frequency has to be high enough that flickering isn't visible.

Reply to
Tom Del Rosso

that's clear enough, it's the bit the OP quoted that was ambiguous

NT

Reply to
tabbypurr

So you didn't actually read the datasheet ?>:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

So you didn't look at the datasheet either ?>:-} (Though you clearly understood.)

Remarkable how many posters DID NOT view the datasheet... yet took it upon themselves to barf snarkily... engineers ?:-( ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

looks to me like the part has 2 modes of dimming using the same input pin:

You can apply a logic level PWM signal 100 Hz to 1kHz or you can apply an analog dim voltage 0 to 2.5 volts.

m
Reply to
makolber

Looks like only a few of the higher-current parts do that. The 700 mA part seems to not.

It's not a very clear data sheet.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

I think we can all agree on that.

GH

Reply to
George Herold

What? Can't pin your own diapers ?>:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

I admit I didn't. Such things are legal documents as well as design guidance, so they need to state the basic specs plainly & clearly, otherwise my suspiciators perk right up.

NT

Reply to
tabbypurr

The analog/pwm input spec on some of the parts somewhat vague. (If I input 1.5 V what fraction of current do I get?) I certainly would want to play with one before I designed it into a circuit.

But sure I like to have a spec sheet that pins the diapers on for me. I'm less likely to embarrass myself that way. :^)

George H.

Reply to
George Herold

There's a graph towards the end of the data sheet.

The data sheet is a bit vague, especially for beginners, but the MeanWell stuff seems to be cheap and good. I've used hundreds of their open-frame off-line switchers. As with most things like this, the best thing to do is get one and test it.

JT thinks that gross insults are neutralized by complex smilies. Very strange behavior.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

Ohh.. I missed it. (Looks like one of my pins came undone, probably won't be the last time. :^)

George H.

Reply to
George Herold

No - got that. I have PWM coming out of a raspberry pi, at around 580Hz, si nce the LDD demands between 100Hz and 1Khz.

I agree using a ULN2803 as a logic device isn't a great plan, but that's wh at is on a board that's already developed, built and tested. (It was origin ally going to drive the LED directly.)

So I built a voltage divider/pullup that applies a safe voltage to the base of the 2n2222 (and the 3 paralleled ULN outputs pulls it down close enough to 0 to turn it off). The output of the collector pulls down on another vo ltage divider, so I get either 7.7v or 0.01v out to the LDD, toggling accor ding to the PWM. No design prizes, but it's working.

I'm not getting anything like linear dimming control, and I had to apply a huge curve to the software setting the PWM duty cycle to even get close, bu t it's good enough.

Not too worried about fires. Everything is within spec, and nothing but the LED gets warm - and that's mounted on a heat sink about the size of my fis t. The light is on for brief intervals with long off times; the longest on time is about 2 minutes, and that period has an average duty cycle of 50%. I'm not one for getting close to absolute ratings, which is why I wanted to understand that LDD spec in the first place.

Thanks to all.

Reply to
thehandsinthedark

No - got that. I have PWM coming out of a raspberry pi, at around 580Hz, si nce the LDD demands between 100Hz and 1Khz.

I agree using a ULN2803 as a logic device isn't a great plan, but that's wh at is on a board that's already developed, built and tested. (It was origin ally going to drive the LED directly.)

So I built a voltage divider/pullup that applies a safe voltage to the base of the 2n2222 (and the 3 paralleled ULN outputs pulls it down close enough to 0 to turn it off). The output of the collector pulls down on another vo ltage divider, so I get either 7.7v or 0.01v out to the LDD, toggling accor ding to the PWM. No design prizes, but it's working.

I'm not getting anything like linear dimming control, and I had to apply a huge curve to the software setting the PWM duty cycle to even get close, bu t it's good enough.

Not too worried about fires. Everything is within spec, and nothing but the LED gets warm - and that's mounted on a heat sink about the size of my fis t. The light is on for brief intervals with long off times; the longest on time is about 2 minutes, and that period has an average duty cycle of 50%. I'm not one for getting close to absolute ratings, which is why I wanted to understand that LDD spec in the first place.

Thanks to all.

Reply to
Scott M

no... that's for models "1000" to "1500", and the analog control is between 0.5 and 2.5

his model "700' only does PWM.

--
This email has not been checked by half-arsed antivirus software
Reply to
Jasen Betts

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.