[Prev][Next][Index][Thread]
Re: RE measuring inductance
Subject: Re: RE measuring inductance
Date: Tue, 06 May 1997 09:21:55 -0500
From: David Huffman <huffman-at-FNAL.GOV>
To: Tesla List <tesla-at-pupman-dot-com>
Hi Group,
I don't believe LEDs have two junctions in series, different diode
types exhibit different forward voltage drops at a given current. For
example germaniums have a typical forward drop of 0.3 volts, schottky
0.5V, silicon 0.7V, red LED 1.7V-at-5ma, yellow LED 1.8V-at-5mA, green LED
2V-at-5mA. If I'm wrong, please let me know. I just want to keep the
spread of information correct.
For measuring L the incandescent lamp is probably best. The LED may
complicate things due to its rectifying action.
Dave Huffman
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: RE: RE measuring inductance
> Date: Monday, May 05, 1997 11:41 PM
>
> Subject: RE: RE measuring inductance
> Date: Mon, 5 May 97 15:36:12 UT
> From: "William Noble" <William_B_Noble-at-msn-dot-com>
> To: "Tesla List" <tesla-at-pupman-dot-com>
>
>
> Your comment about 2 volts is suspicious - LED's are diodes which
emit
> when
> forward biased - depending on the LED, there will be one or more
> "standard"
> diode drops in the forward direction - most red LEDs are a single
diode,
> so
> 0.7 volts will cause them to turn on. I have some green LEDs here
that
> take
> 1.4 volts (e.g. they have 2 diodes in series). You can easily
determine
> what
> you have by putting some current through the LED (with a suitable
> dropping
> resistor) and then measuring the voltage across the LED.
> I would recommend using low power LEDs not the new super bright
ones for
> your
> kind of work - you could use an OP amp circuit and a meter or just
a DVM
> too,
> of course, but the LED is pretty simple.
>
> [Bill] snip
>
> The LED requires a bit more than 2 volts to become forward biased,
> and only then will current *begin* to flow through it. I have one
RF
> Generator that only puts out a measley 2 volts. And it has a
> disgustingly high output impedance. The LED will give decent
visible
> indication beginning at about 1/10th of a milliamp. The series
> resonant circuit has maximum current flow through it at resonance,
> but the LED will only light if the VOLTAGE across the LED exceeds
the
> forward bias point.
>
> [Bill] snip
>