problem with dc-dc converter mc34063 "inverting "

[poohpary]

well ..i designed boost regulator with mc34063 and that worked well (input:7.8 ,output :22, ground:0.3V and....) but i deigned inverting converter with that ic....and does not work...i need output -22V but its output is -8V...design seems correct (due to datasheet)...i dont know what to do....is there anyone who can help me??? plz?

[planet12]

As it happens I'm in the middle of working on one of these at present. Don't worry if you can't answer all my questions, just do your best.

Please point to the exact schematic you are using along with component values, diode types, etc. Be as specific as possible about the inductor, as that's a very core part of all such circuits - eg. is it purchased, scavenged, homemade? Have you confirmed the value? Any idea what the saturation current of it is?

Double check that pin 4 is _not_ connected to ground, as that's a rather important part of the inverting configuration (although if you're getting -8V out this is highly unlikely).

Do you have access to an oscilloscope? If so, screenshot/photograph and post the following measurements: pin 2 referenced to ground (switch output), pin 3 referenced to pin 4 (timing capacitor), and pin 6 referenced to pin 7 (voltage across current sense resistor).

[poohpary]

thanks for reply...it worked with capacitor exchange..!!
but leme ask a Q ...if i want to calculate input power i need average input current or rms? what current is  my source voltage showing? when i used that current showing on source voltage to calculate efficiency , it became  over 100%!!