On Wed, 02 Jul 2008 22:44:53 -0700, Don Bowey <dbowey@[EMAIL PROTECTED]
>
wrote:
>On 7/2/08 7:06 PM, in article zuWak.31133$ZE5.5572@[EMAIL PROTECTED]
>"Bob Eld" <nsmontassoc@[EMAIL PROTECTED]
> wrote:
>
>>
>> "Don Bowey" <dbowey@[EMAIL PROTECTED]
> wrote in message
>> news:C4916A23.BD130%dbowey@[EMAIL PROTECTED]
>>> On 7/2/08 4:14 PM, in article
XXTak.3268$vn7.2496@[EMAIL PROTECTED]
>> "Bob
>>> Eld" <nsmontassoc@[EMAIL PROTECTED]
> wrote:
>>>
>>>>
>>>> <jalbers@[EMAIL PROTECTED]
> wrote in message
>>>>
>>
news:2f8acf53-1cda-424c-9073-6706a1eb55ac@[EMAIL PROTECTED]
>>>>> I am experimenting with a relaxation oscillator circuit consisting
of
>>>>> a NE-2 bulb wired parallel to a capacitor and this pair is wired in
>>>>> series with a resistor and connected across a 150 V DC power source
(a
>>>>> bunch of DC wallwarts connected in series). The resistor is
variable
>>>>> 0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
>>>>> don't have any capacitors on hand with a higher working voltage.
>>>>>
>>>>> The circuit seems to work. I can get the bulb to blink around 3
times
>>>>> a second but I am wanting a higher flash rate and I am not getting
>>>>> it. Lowering the resistance makes the bulb turn on continuously. I
>>>>> don't think that the bulb is fla****ng faster than the eye can
>>>>> distinguish. I conneded the circuit to an oscilliscope and when the
>>>>> bulfb is visually fla****ng I see the RC discharge curve but lowering
R
>>>>> until the bulf truns on continuously pretty much produces a flat
line
>>>>> on the scope.
>>>>>
>>>>> I was expecting to maybe be able to get around 2-100 hz with a NE-2
>>>>> relaxation oscillator. Is this possible or am I expecting too much
>>>>> from this type of circuit? And if so, why?
>>>>>
>>>>> Any help would be greatly appreciated. Thanks
>>>>
>>>> As mentioned above, use a much smaller capacitor. Also, never allow
the
>>>> resistance to go near zero ohms as this can burn out the NE-2.
>>>>
>>>> The Neon lamp is a negative resistance device. To oscillate it has to
>> stay
>>>> in the negative resistance region. The pot is a positive or normal
>> resistor.
>>>> If it's value is adjusted too low, the overall combination resistance
>>>> becomes positive, oscillation stops and the lamp turns full on.
That's
>> what
>>>> you are observing. Keep the resistor value high and the capacitor
small.
>>>>
>>>>
>>>
>>> Actually, it's a relaxation oscillator. The lamp is off when the
voltage
>>> across the cap is less than the firing voltage (about 67 Volts for a
NE2).
>>> When the cap charges to around 67V, the neon ignites and the voltage
>> across
>>> the cap falls from the low resistance "short" and the cycle of
>>> charge-fire-charge-fire continues, creating the typical sawtooth
waveform.
>>
>> That's the definition of negative resistance. When the voltage is high
the
>> current is low or off and when the voltage is low, the current is
high.
>> That's the opposite of a normal resistor where current goes up with
voltage.
>> Relaxation cannot occur without negative resistance.
>>
>> BTW it's possible to make a similar device with two transistors that
will
>> work on a few volts.
>>
>> Another ancient device that exhibits this characteristic is a tunnel
diode.
>> GHz oscillators can be made with them.
>>
>> Look up unijunction trasistor and diac, other devices that exhibit this
>> characteristic.
>>
>>
> Perhaps you could post a link that plots the negative resistance region
of
>a neon lamp?
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news:lnpp64t1q9ohk1d1ar57dhd673pmaif3g6@[EMAIL PROTECTED]
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