Negative voltage source

I have a project using six IV-11 vacuum fluorescent displays. All six vfd are driven by a single MAX6921 vfd tube driver. I use the MAX6921 to power each vfd alternatively. The MAX6921 outputs 50 V or 0 V respectively to power or shutdown a vfd grid. However, 0 V is not sufficient to completly turn off an IV-11; I need about -3 V. So a made a negative power source using NE555 driven negative charge pump.

Now the problem: How to efficiently convert the MAX6921 outputs (0 and 50 V) to the required output (-3 and 50 V). I thought of push-pull transistors, but I can't figure out a working circuit.

(I know the MAX6931 would do exactly what I want, but it comes in TSSOP package only and I am not equipped for surface soldering.)

I don't know VFDs but surely you can just give them 3V as their common voltage, then ground will appear as -3V and 50V as 47V? You then need a buffer to drive a 3V rail (it may need to source current or sink it or both)

Hi DrG, I have in the past used a MAX660 to invert a voltage, but it will only take a max of 5.5V in and give the same, but neg out at upto 100mA, only needs 2 1-150uF caps. It might do the job.

Hope it helps.

Regards

Mel.