Need sooper dooper fast diodes.

Nov 19, 2009 5 Replies
Y

I'm still playing with the inductive coupled charger. I need to get



20w across a gap.

It is begining to look like I might want to go above 1MHz. I was reminded the last time I brought up 500kHz to 1MHz that that was in the middle of AM band. I think the core design becomes easier the higher I go up in frequency anyway.



What is the practical frequency limits based on present diode technology? Can I get a diode that will operate at 2 amps at 5MHz or



10MHz for 50 cents? I seem to recall the regular Schottky diodes in 3 amp SMB package are around 20 cents. I don't think they have th speed tho. Is the SiC or GaAs diode a likely candidate?

Any help would be appreciated.



regards, Bob


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J

Schottly diodes are essentially infinitely fast, down to the picoseconds range. The bigger parts will have serious amounts of junction capacitance, which may resonate out in your application.

SiC and GaAs, in addition to being expensive, will have more forward voltage drop.

John

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J

[snip]

And reverse leakage :-( ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | "I have a dream that [we] will one day live in a nation where [Obama] will not be judged by the color of [his] skin but by the content of [his] character." Obama will then be impeached. "Free at last! free at last! Thank God Almighty, we [will be] free at last!"
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T

Now, they're always claimed to have "zero" reverse recovery current, but the transient just from the capacitance looks an awful lot like reverse recovery. Is it that, in a suitable circuit (lots of L and C around from transformers and parasitics, instead of a test circuit with switching transistors and bias resistors), that gulp of reverse charge is somehow lossless?

Tim

Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
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J

The capacitance is lossless but is nonlinear, which makes things a little weird.

Some schottky diodes have P-N guard rings for some semiconductor-ish reason. At high forward currents, when the schottly drop gets to abount 0.6 volts or so, you can forward bias the PN rings and see reverse recovery from that. So don't push schottky power diodes too hard, or at least experiment to see if this is going to be a problem.

John

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Y

age

the

rom

Ok, thanks for the comments. I'll wind the frequency up and see how they behave.

regards, Bob N9NEO

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