My NE-2 Relaxation Oscillator is Too Relaxed ???
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Posted by jalbers@bsu.edu on July 2, 2008, 4:49 pm
Please log in for more thread options 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 | ||||||||||||||||
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Posted by Andrew Holme on July 2, 2008, 5:01 pm
Please log in for more thread options Try a smaller capacitor e.g. 0.47uF | ||||||||||||||||
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Posted by Bob Eld on July 2, 2008, 7:14 pm
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> 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. | ||||||||||||||||
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Posted by Don Bowey on July 2, 2008, 8:23 pm
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. | ||||||||||||||||
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Posted by Bob Eld on July 2, 2008, 10:06 pm
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 > >
stay
> > 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 > > 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
what
> > becomes positive, oscillation stops and the lamp turns full on. That's > > you are observing. Keep the resistor value high and the capacitor small.
> > > > >
across
> 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 > 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. | ||||||||||||||||
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> 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
>