I'm wondering if someone could help me understand this datasheet better.
I'm looking at this particular E-switch illuminated push button switch
https://sten-eswitch-13110800-produ...em/asset/product_line/data_sheet/251/SAV7.pdf
What I'm trying to figure out is that LED voltage rating that they list. The only ones I can find in stock are the 3V LED variants.
In the LED schematic from the datasheet though, they show the LED portion as just a pair of LED's in opposite orientations, but no limiting resistors.. Is there some reason I couldn't just use 12V or something like that, with an appropriate limiting resistor?
Where would the 3V rating come from?
I'm looking at this particular E-switch illuminated push button switch
https://sten-eswitch-13110800-produ...em/asset/product_line/data_sheet/251/SAV7.pdf
What I'm trying to figure out is that LED voltage rating that they list. The only ones I can find in stock are the 3V LED variants.
In the LED schematic from the datasheet though, they show the LED portion as just a pair of LED's in opposite orientations, but no limiting resistors.. Is there some reason I couldn't just use 12V or something like that, with an appropriate limiting resistor?
Where would the 3V rating come from?
I've used those switches. You must include a limiting resistor. The 3V rating is for the LED's and must not be exceeded.
I'm not sure I understand why there's a voltage rating though. Doesn't an LED have a fairly fixed voltage drop, and you're just limiting current when it's in a circuit?
Like, say I've got a 12V supply, and I'm assuming a 3V drop over the LED, so I decide on a safe amount of current of say 10mA, then I use a ~1Kohm resistor.. Is the voltage rating that they're listing the forward voltage drop of the diode?
If so, how are there other versions of this switch that have a 12V LED voltage rating listed? That seems high for an LED forward voltage drop.
Like, say I've got a 12V supply, and I'm assuming a 3V drop over the LED, so I decide on a safe amount of current of say 10mA, then I use a ~1Kohm resistor.. Is the voltage rating that they're listing the forward voltage drop of the diode?
If so, how are there other versions of this switch that have a 12V LED voltage rating listed? That seems high for an LED forward voltage drop.
I don't see a LED voltage rating on that data sheet. But anyway it is important to know what the voltage needs to be to illuminate the LED. You need it to calculate the resistor depending on your available voltage.
It makes a big difference whether you have 3.3V or 12V available.
Jan
It makes a big difference whether you have 3.3V or 12V available.
Jan
Just assume that a resistor is needed and take it from there. Power it from 12 volt with something like a 2k2 and see where that gets you in terms of brightness.
The inverse parallel configuration means that reverse voltage isn't an issue. Trial and error... non problem 🙂
The inverse parallel configuration means that reverse voltage isn't an issue. Trial and error... non problem 🙂
It's pretty obvious from the specs. The 3 volt rating model is for use in "3 volt" circuits which are pretty common today. Either choose the model that matches the voltage available or use a dropping resistor for the 3 volt model to work at say 12 volts.
Okay so it's saying it can operate with a 3V supply with no limiting resistor I guess?
And if my supply is higher I'll just use a limiting resistor
Using 3V with no resistor is risky. If it is a bit too high you burn out the LED, if it is a little too low there's no light. Better use a higher voltage and a resistor as mentioned.
BTW the two anti-parallel may mean it is dual color, depending on the supplied voltage polarity.
Jan
BTW the two anti-parallel may mean it is dual color, depending on the supplied voltage polarity.
Jan
that line of switches can be custom configured via the part number configurator and has options from 3v to 220v with a numerical designator to select the operational voltage as well as color type and bi color options.
The model number determines operating voltage, color.............. the data sheet gives all the info. The Anti-parallel LED is for AC models and dual color....
What am I not getting here? I see that you can get it in 3V, 6V, 12V, etc.. But is that to say that with the 3V variant, I couldn't just use a 12V supply with an appropriate current limiting resistor? Doesn't an LED have a fixed voltage drop, and always require a current limiting resistor?
So regardless of what my supply voltage is, if I use an appropriate current limiting resistor I'm okay..? The only downside to a larger supply voltage would be greater power consumption in the limiting resistor.
The linked datasheet clearly states:
so I am quite certain that each switch already includes approppriate current limiting resistors
Which is confirmed by the NOT inclusion of a LED current rating and/or table of suggested resistor ratings depending on voltage.
Inb fact, they offer a "Part Number Configurator" table where you choose illuminating voltage before ordering.
Quite clear and to the point.
Only problem is they do not show the internal current/voltage setting resistor i9n the schematic, maybe you "should" assume it´s there without further explanation.
EDIT:
I´d start with, say, 5mA, those Leds might be high efficiency.
In no case I would exceed 20mA.
I bet those are not "3V Leds" but plain 1.9 / 2.2 / 2.5V Leds (depending on colour) with a proper built-in resistor, in that case what works with 3V supply.
so I am quite certain that each switch already includes approppriate current limiting resistors
Which is confirmed by the NOT inclusion of a LED current rating and/or table of suggested resistor ratings depending on voltage.
Inb fact, they offer a "Part Number Configurator" table where you choose illuminating voltage before ordering.
Quite clear and to the point.
Only problem is they do not show the internal current/voltage setting resistor i9n the schematic, maybe you "should" assume it´s there without further explanation.
EDIT:
They want to sell you voltage specific models, fine with me and avoids guesswork, but I guess if you want to use a certain model with higher supply vokltage, you also can, adding proper resistor.
I´d start with, say, 5mA, those Leds might be high efficiency.
In no case I would exceed 20mA.
I bet those are not "3V Leds" but plain 1.9 / 2.2 / 2.5V Leds (depending on colour) with a proper built-in resistor, in that case what works with 3V supply.
Last edited:
Your over thinking this. Data sheets have been like this for decades. The model number you order determines the specs of the switch. Do you even know what model you want?
Perhaps I should assume that, but it seems risky to power up an LED with no limiting resistor, so I'd hate to try a 3V supply and just assume it's in there.
And the schematic does not show one.
And the schematic does not show one.
Attachments
Last edited:
The diagram is simplified as it is on many data sheets of products with multiple configurations. Blame the requirement of wanting less pages in the catalog...
Yes I know exactly which one I want, but I want to make sure I'm powering the LED correctly. And there only seems to be availability in the 3V variants.
If the datasheet shows the LED circuit as simply containing 2 LED's in opposite orientations, then shouldn't I assume that's all that's in the switch?
And if that's all that's in the switch, then why couldn't I treat it like I would any normal LED?
The part I'm looking at is the 3V version (because I can only find it in 3V version in stock anywhere in black with latching switch and red circle LED). So I will just build a regulated 3V power supply.. I thought maybe I could just tie into an existing 12V supply in the device I'm building and use a current limiting resistor.
