Figure shows the basic configuration of a relaxation oscillator using a neon lamp. This circuit is suitable to frequencies up to some tens quilohertz and operates from power supply voltages over 80 volts.

A typical neon lamp breakes down at 70 V and establishes a glow and this glow is extinguished when the voltage accross the lamp is reduced to 50 V. The next formula is valid to these parameters.

**Formula 1 **

Period:

** Where: **

T is the period in seconds (s)

C is the capacitance in farads (F)

R is the resistance in ohms (Ω)

U is the power supply voltage in volts (V)

Ut is the triggering voltage in volts (V) - 70 V typ.

µH is the holding voltage in volts (V) - 60 V typ.

**Formula 2 **

Frequency:

**Where: **

f is the frequency in hertz (Hz)

C is the capacitance in farads (F)

U is the power supply voltage in volts (V)

Ut is the triggering voltage in volts (V)

µH is the holding voltage in volts (V)

**Application example: **

In the circuit shown in figure bellow the resistance between gate and cathode of the SCR in the on state is not considered. Determine the frequency of the produced flashes:

**Data: **

R = 1 MΩ = 10^{6} Ω

C = 10 µF = 10 x 10^{-6} F

U = 150 V

Ut = 70 V

µH = 50 V

f = ?

**Applying formula 2:**