MC34063 , US1M vs schottky diode

[Drirr]

Hi,
I have a simple, cheap side project where I wanted to use my old trusty MC34063.
Input voltage: 24V, output: 5V @ 300mA… what could possibly go wrong?

I bought an MC34063 at a local store and put everything together. And… a problem occurred. At just 100mA the MC34063 overheated and died.

So I thought maybe I had bought a fake IC. I switched to a TI MC34063, but the same thing happened.

I tried different capacitors (ceramic, electrolytic), different inductors… nothing helped. The only difference was that instead of a Schottky diode I used a US1M fast diode (from mouser.com). Efficiency wasn’t important to me.

When I replaced it with a Schottky, everything worked fine. But why??? 🤦

[gamalot]

I've been playing around with a 34063 boost circuit lately. While its efficiency and ripple aren't ideal, it's cheap, simple, and reliable.

I've always used Schottky diodes and never had any problems. The reverse recovery time of the US1M diode you're using is 50ns, and as far as I know, the reverse recovery time of Schottky diodes can be considered zero.

[Drirr]

I've always used Schottkys too, but I have no idea why using a standard diode is a problem. 50ns still seems pretty fast. Or maybe there’s something fishy about the US1M...