# Do you have a resonant inverter schematic?

Discussion in 'The Projects Forum' started by wayneh, Aug 10, 2014.

1. ### wayneh Thread Starter Expert

Sep 9, 2010
12,151
3,058
I'm looking for a simple, DIY schematic for a resonant inverter to operate at 400Hz to 2kHz, to provide 10-15W into the load.

As I study the properties of electroluminescent (EL) tape, I'm learning it is somewhat "fragile". The brightness of EL tape is degraded over time by high frequency and excessive voltage, and perhaps by current surges. It will extend the life of the EL tape if I can power it with a gentle sine wave instead of a pounding square wave. So I need a circuit to convert my square wave clock signal into a sine wave. It appears that this is a job for a resonant inverter such as an LLC resonant circuit.

The wrinkle with EL tape is that the tape itself is capacitive and would serve as the "C" in a resonant LC circuit. The "L" and the clock frequency need to be tuned to the circuit to work with the low C value of the EL tape (e.g.. 360nf). At the low frequency and low C value, the value of L is large and may be prohibitive? CFL drivers use resonant converters but at much higher frequency, so the inductor parts are smaller.

I've already played around with placing an inductor in series with the EL tape, to soften current spikes it would otherwise see when pulsed by a square wave from a push-pull amp. The inductor rounds the edges (and rings), but again the value of L gets up into impractical values if I use a value large enough to produce a sine wave. At the larger sizes, with good resonance that looks like a sine wave, I see also that the voltage across the EL tape nearly doubles.

Last edited: Aug 10, 2014
2. ### Dodgydave Distinguished Member

Jun 22, 2012
4,999
745
wayneh likes this.
3. ### wayneh Thread Starter Expert

Sep 9, 2010
12,151
3,058
I think what I'm coming to is that I'm going to need a specialized transformer/inductor as the key component. My box of old wall warts may not be the answer I had hoped for.