• Infernorage
In summary, the Pearson-Anson relaxation circuit is used to blink neon lamps. The lamp does not permit a current until the capacitor reaches the voltage threshold, causing the gases in the lamp to ionize and a sudden current. Once the capacitor discharges enough, the voltage falls below the lower threshold, the current drops to zero, and the power source begins charging the capacitor again to repeat the process.
Infernorage
As seen in the circuit diagram picture below, the Pearson-Anson relaxation circuit is often used to blink neon lamps. According to what I have read, the lamp does not permit a current until the capacitor reaches the voltage threshold, causing the gases in the lamp to ionize and a sudden current. Once the capacitor discharges enough, the voltage falls below the lower threshold, the current drops to zero, and the power source begins charging the capacitor again to repeat the process.

My question is, why doesn't the battery just turn on the lamp and keep it lit while charging the capacitor. The voltage of the capacitor will never exceed the battery so the battery must have enough voltage to turn the lamp on. Also, since the lamp is in parallel, isn't the voltage difference across the lamp the same as that of the capacitor? I don't see why the battery wouldn't just light the lamp right away. Can anyone clarify this for me? Thanks in advance.

Infernorage said:
My question is, why doesn't the battery just turn on the lamp and keep it lit while charging the capacitor.
Because, once the voltage across the neon lamp increases beyond its threshold voltage and begins to conduct, the lamp acts like a short circuit which discharges the capacitor. Re-analyze the circuit treating the neon bulb as a short circuit when the lamp is on.

gnurf said:
Because, once the voltage across the neon lamp increases beyond its threshold voltage and begins to conduct, the lamp acts like a short circuit which discharges the capacitor. Re-analyze the circuit treating the neon bulb as a short circuit when the lamp is on.

I understand why the capacitor discharges, but I suppose my problem is with what happens before the voltage threshold. The lamp is parallel to the capacitor, so I figured the voltage difference of the power source would also be across the lamp, but that would immediately light it. Why isn't the batteries voltage difference initially applied to the neon lamp?

Infernorage, It seems you’ve copied the schematic drawing from the wiki page http://en.wikipedia.org/wiki/Pearson–Anson_effect

If you have not done so yet, may I suggest you read the two paragraphs just below the diagram labeled “Charging” and “Discharging” where the operation of the circuit is discussed with elegant clarity.

If then you have some doubts or questions about the operation, please return here and post them. Members here are always willing to assist any true searcher for understanding of the mysteries of our natural world.

Cheers,
Bobbywhy

Infernorage said:
I suppose my problem is with what happens before the voltage threshold. The lamp is parallel to the capacitor, so I figured the voltage difference of the power source would also be across the lamp, but that would immediately light it. Why isn't the batteries voltage difference initially applied to the neon lamp?
The lamp is basically an open circuit below its threshold, so that part of your problem is reduced to understanding the transient behavior of a simple RC circuit. You wouldn't expect a capacitor that is charged with a current limited (as in the resistor) voltage source to instantly reach the supply voltage, would you?

The lamp also has two thresholds.
Before it fires, it draws no current and produces no light.
Once it fires, (that is, when the voltage across it reaches the first threshold), it draws current and produces light as it gets current mostly from the capacitor and some from the resistor.
It then reaches the second threshold when the voltage across the lamp is not enough to maintain conduction. So the lamp switches off and the capacitor starts to charge up via the resistor.

These devices usually operate at a relatively high voltage of about 60 volts and this circuit produces a crude but large sawtooth waveform across the capacitor.

The value of the resistor is important for this to work. If R is too small, there will be a delay while C charges up to the threshold voltage, and then the lamp will be permanently on, as the OP suggested.

R needs to be big enough so the battery can't maintain the lamp voltage on its own, because of the voltage dropped across R.

C acts like a "second battery" to keep the lamp voltage high, but the voltage falls as C discharges, until the lamp goes off and the battery can then recharge C to repeat the process.

Incidentally, you can make a low voltage version of this using an Schmidt trigger IC instead of the neon lamp, and you can make a similar oscillator with the common "555" IC. Experimenting at 5V is much safer than messing around with 60V or 90V neon lamps!

1. What is the Pearson-Anson Relaxation Circuit?

The Pearson-Anson Relaxation Circuit is an electronic circuit used to measure the relaxation time of a material. It was first developed by British physicist George W. Pearson and American electrical engineer John A. Anson in the early 20th century.

2. How does the Pearson-Anson Relaxation Circuit work?

The circuit consists of a capacitor, a resistor, and a voltage source. The capacitor is charged to a certain voltage and then discharged through the resistor. The time it takes for the capacitor to discharge to a certain percentage of its original voltage is measured and used to calculate the relaxation time of the material.

3. What is the purpose of using a Pearson-Anson Relaxation Circuit?

The circuit is commonly used in materials science and engineering to determine the relaxation time of materials. This is important for understanding the physical properties and behavior of materials, such as in the design of electronic devices and materials used in energy storage applications.

4. How accurate is the Pearson-Anson Relaxation Circuit?

The accuracy of the circuit depends on various factors such as the quality of the components used, the measurement equipment, and the handling of the circuit. However, with proper calibration and careful handling, the circuit can provide accurate results within a reasonable margin of error.

5. Are there any limitations to the Pearson-Anson Relaxation Circuit?

The circuit is most suitable for measuring the relaxation time of materials with simple exponential decay behavior. It may not be suitable for materials with more complex relaxation behavior, and other measurement techniques should be used in those cases. Additionally, the circuit may be affected by external factors such as temperature and electromagnetic interference, which should be minimized for accurate results.

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