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.
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