My NE-2 Relaxation Oscillator is Too Relaxed ???
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Posted by Don Bowey on July 3, 2008, 1:44 am
Please log in for more thread options >
>> On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com,
> "Bob
>>
>>>
>>> >>>> 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 flashing faster than the eye can >>>> distinguish. I conneded the circuit to an oscilliscope and when the >>>> bulfb is visually flashing 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. >
Perhaps you could post a link that plots the negative resistance region of
> 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. > > a neon lamp? | ||||||||||||||||
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Posted by John Fields on July 3, 2008, 10:53 am
Please log in for more thread options >On 7/2/08 7:06 PM, in article zuWak.31133$ZE5.5572@nlpi061.nbdc.sbc.com,
> >>
>>> On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com,
>> "Bob
>>>
>>>> >>>> >>>>> 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 flashing faster than the eye can >>>>> distinguish. I conneded the circuit to an oscilliscope and when the >>>>> bulfb is visually flashing 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? --- JF | ||||||||||||||||
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Posted by Don Bowey on July 3, 2008, 11:57 am
Please log in for more thread options On 7/3/08 7:53 AM, in article 8spp64hncghn88d0gqbensnerupo39h4k0@4ax.com,
> wrote:
> >> On 7/2/08 7:06 PM, in article zuWak.31133$ZE5.5572@nlpi061.nbdc.sbc.com,
>> >>>
>>>> On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com, >>> "Bob >>>> >>>>> >>>>> >>>>>> 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 flashing faster than the eye can >>>>>> distinguish. I conneded the circuit to an oscilliscope and when the >>>>>> bulfb is visually flashing 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? >
> --- > > JF Thanks. I had already thought more about the neon lamp and decided it could have, or appear to have, a negative resistance region, so I did some google work and found several trustworthy articles supporting it. I also found one credible article saying the effect is not negative resistance, but...... If it quacks like a duck it's probably a duck. IMHO the typical neon tube relaxation "oscillator" does not use that effect, however, but uses the gross cap discharge to begin a next charge cycle. The external R must be high enough to allow the voltage across the tube to fall far enough to extinguish the lamp. This will be a good slow-day plaything. I think I'll put a parallel resonant circuit in series with the lamp and variable voltage source....... | ||||||||||||||||
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Posted by John Fields on July 3, 2008, 1:11 pm
Please log in for more thread options wrote:
>On 7/3/08 7:53 AM, in article 8spp64hncghn88d0gqbensnerupo39h4k0@4ax.com,
> >> wrote:
>>> Perhaps you could post a link that plots the negative resistance region of
>>> a neon lamp? >>
>> --- >> >> JF >
>Thanks. > >I had already thought more about the neon lamp and decided it could have, or >appear to have, a negative resistance region, so I did some google work and >found several trustworthy articles supporting it. I also found one credible >article saying the effect is not negative resistance, but...... If it quacks >like a duck it's probably a duck. > >IMHO the typical neon tube relaxation "oscillator" does not use that effect, >however, but uses the gross cap discharge to begin a next charge cycle. --- I agree, and stated that in an earlier post. :-) --- >The external R must be high enough to allow the voltage across the tube to fall
>far enough to extinguish the lamp. --- Yes, and when the gas in the tube deionizes to the point where current through it falls to a low enough level, the "striking voltage" must then be raised high enough to once again start the ionization. --- >This will be a good slow-day plaything. I think I'll put a parallel
>resonant circuit in series with the lamp and variable voltage source....... --- Sounds like fun. :-) If you want to you can go here: http://www.duntemann.com/12vtubes/datasheetsindex.htm and download all 80 megabytes (!) of the GE glow lamp manual. JF | ||||||||||||||||
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Posted by John Fields on July 2, 2008, 11:13 pm
Please log in for more thread options wrote:
>
>> 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 flashing faster than the eye can >> distinguish. I conneded the circuit to an oscilliscope and when the >> bulfb is visually flashing 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. --- Not true. It exhibits negative resistance characteristics over its glow range, but in order to work as a gross relaxation oscillator it has to break out of the negative resistance region by discharging the parallel capacitor through the plasma to the point where it can no longer support conduction and then return to the more-or-less deinozed state where the glow is extinguished and the cycle is started anew with the capacitor charging up to the ionization voltage. --- >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. --- Good advice, but the deionization time of the gas in the tube will be the ultimate determinant of the relaxation oscillator's high frequency. JF | ||||||||||||||||
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