Electronic – Negative level shifter


I need to connect two circuits that use different PSU voltages.
The first is a microcontroller clock generator, it outputs a clock 0V to 3.3V at 150KHz as maximum freq.
I need to connect this clock to a CD4047 (pin.3) on the second circuit. But the second circuit uses negative supply voltage and I cannot change that. So the CD4047 is powered with -15V and 0V.
Obviously it won't accept my clock as is.
I think I need a level shifter that converts the positive level of the clock to -15V or lower (I don't mind about the phase of the clock).

I tried the circuit shown in Figure 2 here:
I used a LM393 instead of the comparator used in that schematic, and powered it with 0V on pin 8 and -15V on pin 4
But it didn't work, maybe I got something wrong

Do you have any example tha I could use, or a different approach to do this task?
Thank you

Best Answer

I'd rather go with a simple common base level shifter


simulate this circuit – Schematic created using CircuitLab

R1 is choosen not to saturate Q1 looking for "high speed" turn-off. In this conditions fall time is mostly ruled by R2 and output stray capacitance.

Output clock more probably swings from 0V to around 13V w.r.t the -15V line. This should be more than adeguate to 4047 input.