Hysteretic buck converters

Duh! You can make that type of converter from an LM339. Did it all the time at GenRad, 1977-1987.

...Jim Thompson

I notice that Natsemi has jacked up the prices of their LM500x hysteretic converters by over 60% (1K price in USD).

What's with those guys, they want to abandon the low end analog to others?

Best regards, Spehro Pefhany

Hello Spehro,

That's are sure-fire way to kill a technology. It is what has brought down switched capacitor filters, IMHO. The chips were too expensive. I used them in exactly one design.

I don't understand the marketing logic behind that either. Abandoning the low end would be like Toyota abandoning their Corolla (which is a nice car). It's hard to come up with even a brief list of companies that has survived such strategy over for long.

Regards, Joerg

Hello Jim,

So did I and still do, although I prefer logic chips. Looking back at all my switcher designs I'd bet that >50% did not contain any PWM chip.

But it's a bit more involved than a lone LM339. For a sufficiently high frequency and small magnetics you need brawny drivers (hence logic chips) and some dead-time control for a synchronous scheme.

BTW, was that the switcher where a guy convinced you that the design wasn't fool-proof by rocking the power switch up and down until the guts blew out?

Regards, Joerg

Hysteretic buck is probably the oldest and simplest switcher topology of all. I did these in the early 70's, using an uncompensated LM709 as the comparator and a PNP-NPN pair (2N2905 PNP driving a nonsaturating

John

I'm of the "iron" school ;-) (At least for simple-minded buck designs.)

No. The one that blew was an off-line switcher... straight from

...Jim Thompson

Hello Jim,

I never quite warmed up to laminate cores. So I guess I am a "ferrite" guy. Unless you count iron powder into the iron class but I've never used much of that in designs either. Always tried to keep things at least above the audible range of dogs and cats.

Back at the university there was an unspoken rule not to run heavy stuff below 80kHz. That's because there is a time signal transmission at

Regards, Joerg

Hello John,

That's another reason why I don't understand how they could possibly ask so much money for these chips. One of their chips gets around the ESR issue with hysteretic converters to keep the frequency in check but AFAICT it vanished.

Regards, Joerg