Tinkering with the MC34063, what kind of timing capacitor?

Thread Starter

Evil Lurker

Joined Aug 25, 2011
I do a lot of scavaging and have several of these ICs in my junkbox and figured I would build a DC boost converter. The question I have is what sort of timing capacitor should I use?

I'm thinking of going with a radial leaded multilayer monolithic capacitor vs one of the orange disc capacitors but don't know very much about them. I know how to read the values, its the dielectric material (specifically the temperature coefficient) that I'm concerned about and whether or not it makes a hill of beans difference in practice.

I've got them on plenty of junk boards in all sorts of values coming in yellow and blue flavors, with various letter markings below the number values however I'm unable to identify what is what.

Could anyone shed some light on what these letters mean? Nothing seems to match any of the datasheets from various manufacturers I have looked at.

I'd take pics but unfortunately my camera batteries are dead.


Joined May 9, 2009
It makes very little difference. The capacitor only controls the oscillator frequency, and the on-chip oscillator isn't particularly accurate. A drift in frequency will only slightly change the parameters of the circuit.