Help with relaxation oscillator

  • Thread starter JFS321
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In summary: The DIAC is a circuit made up of two transistors, one in series with the other. The series transistor conducts current only when the voltage on the collector is above the emitter voltage. Otherwise, it blocks the current.So the DIAC behaves like a switch, turning on when the voltage is high and turning off when the voltage is low.The capacitor in the neon bulb relaxation circuit is like the emitter of the series transistor, it blocks current when the voltage on the capacitor is above the threshold voltage.When the capacitor starts to discharge, the voltage across it starts to drop, and that drop causes the current to flow through the neon.The capacitor gradually restores its charge, and the
  • #1
JFS321
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All, I am confused as to exactly how the capacitive relaxation oscillator works.

upload_2015-2-22_18-37-10.png

From the diagram above: Because the lamp is in parallel, why is it not immediately receiving the voltage necessary to light instantly? Thanks.
 
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  • #2
hi there

The neon globe has a minimum strike voltage ... let's say ~ 80V ( 75 - 90V common)
This is the neon's threshold voltage. That voltage will only be reached when the capacitor is charged to that threshold voltage
The neon will then conduct with a flash of light and the voltage across the capacitor will drop to well below the threshold voltage.
The capacitor will then start charging again till that voltage is reached and the neon then discharges again.
this cycle continues on and on ...

The cap doesn't charge instantly ( or near) because of the series resistor limiting current to the capacitor causing it to take time to charge
but when threshold is reached it discharges almost instantly ... ie. it oscillates with a sawtooth pattern

cheers
Dave
 
  • #3
Ahhh ok...so a capacitor acts like a voltage sink of sorts...instead of this being like a regular parallel circuit, the voltage across both legs is initially zero because the capacitor must first charge? Or maybe to reword, the battery voltage does not initially reach the bulb because it is being taken by the capacitor? Thanks-
 
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  • #4
Yes, initially, at time T=0, the capacitor "looks" like a short circuit, charge is flowing onto one plate and out of the other plate
as the charge builds up, the voltage potential difference across the capacitor also does. Only when that voltage potential equals the
discharge ( threshold ) voltage of the neon globe will current flow across the gap in the neon

JFS321 said:
Or maybe to reword, the battery voltage does not initially reach the bulb because it is being taken by the capacitor? Thanks-

The same voltage that is across the capacitor is also across the neon globe, from the time the capacitor starts charging,
that voltage slowly rises as the capacitor charges up
have a look at this ...

relaxation oscillation.jpg
cheers
Dave
 
  • #5
The Neon bulb (gas discharge tube) relaxation circuit is a negative resistance oscillator.
350px-Neon_bulb_relaxation_oscillator_hysteresis_curve.svg.png


The operational voltage and currents are normally designed to be in the unstable portion of the bulbs VI curve.
http://www.g3ynh.info/disch_tube/intro.html
 
  • #6
Thank you.
 
  • #7
Curiously, there is a semiconductor component that behaves like this, the DIAC.
http://en.wikipedia.org/wiki/DIAC

Unfortunately, it lakes the charming flash-flash-flash of the neon bulb.
 

1. What is a relaxation oscillator?

A relaxation oscillator is an electronic circuit that generates a repetitive waveform, typically a square wave or a triangle wave, without the use of a continuously operating feedback path. It relies on the charging and discharging of a capacitor to produce the oscillations.

2. How does a relaxation oscillator work?

A relaxation oscillator works by using a capacitor and a resistor in a feedback loop. The capacitor charges and discharges through the resistor, causing the output voltage to oscillate between high and low states. The duration of the high and low states determines the frequency of the oscillations.

3. What are the applications of a relaxation oscillator?

A relaxation oscillator has many practical applications, including in electronic devices such as clocks, timers, and pulse generators. It is also used in various types of sensors, such as vibration sensors and light sensors, to convert a non-electrical signal into an electrical one.

4. How do you calculate the frequency of a relaxation oscillator?

The frequency of a relaxation oscillator can be calculated using the equation f = 1/(2RC), where f is the frequency in Hertz, R is the resistance in ohms, and C is the capacitance in farads. The frequency can also be adjusted by changing the values of R and C.

5. Can a relaxation oscillator be used for meditation or relaxation purposes?

While a relaxation oscillator can produce a soothing sound, it is not typically used for meditation or relaxation purposes. Its main function is to generate precise and repetitive oscillations for electronic applications. However, some people may find the sound of a relaxation oscillator to be calming and use it for relaxation techniques.

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