gelbanana wrote:Good point erdabyz. I know the 555 outputs at 32kHz, fixed 50% duty cycle, the MC34063 40kHz not sure if it does pwm. Switching speed seems ok with the the bleeder resistor used.
Anyways I've measured the inductors and they are 1mH instead of the suggested 100uH. Could this be the cause of the poor efficiency?
Any thoughts on using lower Vf diodes? Since they are the main loss in a dc-dc converter. The UF4004 is commonly used and it has a max Vf of 1v. I've searched in E14 and the lowest Vf max fast recovery diode is 0.82v.
My nixie clock uses a BYV27-400 as the switching diode. It's an ultra fast recovery power schottky diode. The -400 version is quite hard to find, they usually have the -200 and the -600. I found mines at futurlec. 1mH looks like too much inductance, but the real problem comes with the DC resistance. Being the size they are, those inductors will likely have a lot of turns with small diameter wire, causing them to be fairly resistive. That's not good for a DC-DC converter. Maybe you can look at coilcraft. They have proper power inductors with very low DC resistance and they send free samples of them.