AN3973

DC-AC converter

Doc ID 022164 Rev 1

13/24

Resonant circuit frequency:

Equation 6

3.1.3

Steady-state phase

Once the tubes are ionized, it is effectively a short-circuit across C10 + C11. The inverter

system sets the voltage and current shape so that the lamp correctly operates.

Therefore, the frequency is defined by C15 and so is lower than the ignition phase. At this

frequency, the overvoltage generated is also lower, but enough to keep the tube lit. During

steady-state, when the transistor is first turned on, the current in the transformer L4

increases until its core saturates. At this point, after the storage time of the transistor has

passed, it turns off. In this way, the operating frequency also depends on the size and

maximum flux density of the core of L4 and the storage times of the transistor.

)

C

C

(

L

2

1

f

10

10

3

r

+

π

=

Figure 10.

Voltage and current lamp

waveforms

Figure 11.

Zoom of the highlighted section (in

Figure 10)