My NE-2 Relaxation Oscillator is Too Relaxed ???
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Posted by John Larkin on July 2, 2008, 10:55 pm
Please log in for more thread options Smaller cap. Then, for fun, put two neons in parallel. Then try waving hands around, shinging lights on them, whatever. John | ||||||||||||||||
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Posted by Phil Allison on July 3, 2008, 1:09 am
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> 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? ** The neon's conduction current must be able to reduce the voltage on the cap to below the neon's extinguishing voltage in order for there to be oscillations. If the series resistor is too low in value - this will not happen. So use a small cap - like 10nF and try again. ...... Phil | ||||||||||||||||
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Posted by petrus bitbyter on July 3, 2008, 7:59 am
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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 > You'd first of all read the specifications of the NE-2. Like a lot of neon bulbs it ignites at about 90V. It is the rating for DC but that's half the truth. It will ignite when the voltage accross its leads reaches that 90V. That's where the 65Vac comes from. A 65Vac RMS sine will peak at about 90V. Once the bulb has ignited, the voltage accross its leads sinks to about 60V, regardless of the current. So you have to make a provision to keep the average current at or below 0.5mA where it is rated for. More current will reduce the lifetime of the bulb or may even destroy it. The bulb will extinguish when the voltage across its leads sinks below 60V. You may not find this 60V in the specifications as this value varies. Most of the times it is not specified at all. So the mecanism of a relaxation oscillator will be clear. The capacitor is charged via the resistor. Once the voltage reaches 90V the bulb ignites and discharges the capacitor until the voltages sinks to about 60V. Then the bulb extinguishes and the capacitor will start to charge again. But... once the bulb has ignited, the current through the resistor adds up with the discharge current of the capacitor. If that "resistor" current is enough to keep the bulb going, it will not extinguish. So you cannot lower the resistor too much as it controlls the current. The frequency of your oscillator depends on the resistor and the capacitor value. They determine the time required to charge the capacitor from 60V to 90V. Once the bulb ignites, discharging goes fast. This time can be neglected with respect to the charging time. So once you reaches the lowest value of the resistor, you can only lower the capacitor value to raise the frequency. Using the right components, frequencies of several kHz should be possible. petrus bitbyter | ||||||||||||||||
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Posted by Mark Zenier on July 3, 2008, 6:27 pm
Please log in for more thread options >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 Digging out my GE Glow Lamp Manual, for a 5AB (the tight spec. equivalent to an NE-2) the resistance range for oscillators runs from .5 meg up to 15 meg. To get 100 Hz, you need to run with a .01 uF capacitor and 1 to 5 megohm, depending on voltage (100-150 volts). The maximum frequency, with a capacitor in the 10-30 pf range, is 3 to 30 kilohertz. Mark Zenier mzenier@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com) | ||||||||||||||||
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Posted by Rich Grise on July 7, 2008, 7:49 pm
Please log in for more thread options On Wed, 02 Jul 2008 13:49:49 -0700, jalbers@bsu.edu 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. I also vote "smaller cap", but I'd add to this: There should be a 220K or so (I wouldn't go below about 180K) in series with the pot so that when you turn the pot down, you don't burn out the bulb. I guess you'd size the R so that with your supply you'd want to limit the neon current to the ~1-2 mA range. Have Fun! Rich | ||||||||||||||||
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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