English: The IV curve (characteristic curve) of a neon bulb relaxation oscillator (top) showing the hysteresis loop (abcd) of the oscillation, and the resulting output voltage waveform (bottom). A neon bulb relaxation oscillator consists of a capacitor which is charged from a voltage source V₀ through a resistor R₂, with a neon bulb across the capacitor which discharges it once it reaches the bulb's breakdown voltage V_b. Ths hysteresis curve (abcd) shows the detailed cycle:

• a-b: The voltage across the bulb rises slowly from zero as the capacitor charges, through a to b, where it reaches the breakdown voltage V_b of the bulb. The gas in the bulb ionizes and it become conductive.
• b-c: The charge from the capacitor begins to flow through the bulb, instantly increasing the current to point b in the "abnormal glow" region of the curve. The bulb turns on.
• c-d: The voltage across the bulb and capacitor drops quickly to the extinguishing voltage V_e at which the voltage is insufficient to continue ionizing the gas.
• d-a: The current through the bulb drops to a very low level, and the bulb turns off. This allows the current from the resistor R₁ to begin charging the capacitor up again from a to b and the cycle repeats.

The circuit generates a sawtooth wave, (bottom) alternating between V_e and V_b. The center blue line is the load line, with a slope equal to the resistance R₂. In order for the circuit to oscillate, the load line must intersect the IV curve in it's negative resistance region (red) the segment from b to d, where it is declining to the right:

• If the resistor has too large a value, shown by line R₃ so the load line intersects the curve in section a-b, the resistor current will be so low that the bulb leakage current will bleed the capacitor charge away and the voltage will never reach V_b.
• If the resistor is too small, so the load line intersects the curve in section c-d, shown by line R₁, the current through the resistor will be large enough to keep the bulb turned on, and it won't reach the extinguishing voltage V_e.

Information from C. R. Daugherty, et al, General Electric Glow Lamp Manual, 2nd Ed., General Electric, Cleveland, Ohio, 1966