!!! 1997 G3 MiniTower power button LED !!!

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TheUltimateMacUser's picture
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The green power button LED for my 1997 G3 MiniTower needs replacing. Does anyone know what voltage LED to use?

Thanks

[move]Please Help![/move]

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driver

Use any LED you want. The LED output has a transistor drive circuit that limits the current dynamically to about 20mAh.

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TheUltimateMacUser's picture
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So, I dont have to worry abou

So, I dont have to worry about putting an LED with too high a voltage requirement in there?

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Re: So, I dont have to worry abou

TheUltimateMacUser wrote:

So, I dont have to worry about putting an LED with too high a voltage requirement in there?

no! ... for example running 10v LED on a 5v supply will just result in a dim LED Wink ... however running a 5v LED on a 10v supply will result in a pop and a smell of burning Tongue

TOM

TheUltimateMacUser's picture
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I want to err on the side of

I want to err on the side of caution, so, does a 5 volt LED leave enough of a safety margin, or should i go higher?

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Re: driver

Logic curcuits are almost always 5V and less. The voltage rating is a maximum figure... see "Ohm's Law".

drbob wrote:

Use any LED you want. The LED output has a transistor drive circuit that limits the current dynamically to about 20mAh.

SCSI Hard Drive activity LEDs do that too... I think mostly at slightly less current.

TheUltimateMacUser's picture
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I did it

Ok ,guys n gals, i ran out ot Radio Hack today for an LED. I got a 5mm blue LED with a max. voltage of 4.5 volts. It is working fine and it looks freakin awsome ;D Oh, btw, the LED cost me about $3.00 and change with the sales tax.

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Re: So, I dont have to worry abou

tomlevens wrote:
TheUltimateMacUser wrote:

So, I dont have to worry about putting an LED with too high a voltage requirement in there?

no! ... for example running 10v LED on a 5v supply will just result in a dim LED Wink ... however running a 5v LED on a 10v supply will result in a pop and a smell of burning

As I mentioned above, the current is limited as part of the circuit. This means that the system increases the voltage until the current being drawn matches whatever it's set at. LED's are not really voltage driven devices (beyond a minimum). They are current driven devices. I could drive one off 120 V if I wanted to without any harm.

The voltage rating of the LED is only the minimum voltage required to get it to light up.

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Re: driver

DanR wrote:

Logic curcuits are almost always 5V and less. The voltage rating is a maximum figure... see "Ohm's Law".

Again this is not relevant since the LED driver in that machine already current limits. The voltage rating is a minimum figure, NOT a maximum figure. Finally, the LED driver circuit in that machine is powered off the 12V rail, so it can raise the voltage up to 12V in order to source the requisite 20mAh of current.

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Bob is correct. Current is a

Bob is correct. Current is a maximum figure, voltage will go to what ever is needed to reach that current. Voltage is just a way of regulating current, voltage doesnt kill components, the rise in current do to the voltage being changed is what does.

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Re: driver

(Dang, this thing doesn't preview a quote within a quote right)

Yep, I screwed that up... looked at too many "LEDs for Dummies" websites. Lips Sealed

My local Ratshack is pretty pathetic about keeping up their stock. Undecided They've never had the 4.5V - 20 mA LED, so I picked up a 5V - 30 mA one.
I haven't tried it yet (too many projects), but I'm thinking that even if works on my 7500/G3 I'm not going to be all that happy... the "typical wavelength is 430nm" would probably be too purple. I'll probably order in some other blue LEDs, just to see what they're like.

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Re: driver

DanR wrote:

the "typical wavelength is 430nm" would probably be too purple. I'll probably order in some other blue LEDs, just to see what they're like.

430 is well into the purple range. Also those require an extraordinarily high drive voltage, and may be dimmer than optimal on a standard LED driver.

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