That¡¯s disappointing. There is another layer of the onion yet to peel, apparently.
The better data sheets show you the test circuit, while others just give you the test currents and leave the rest to your imagination. The idea is this:
1) Forward bias the diode at some current I1 (say, by hooking it up as a half-wave rectifier, driving it with some voltage, and loading with some resistor). Leave it on long enough to reach steady state. The value of I1 should be specified by the manufacturer.
2) Flip the polarity of the drive. The diode current will decay in some fashion. Measure the time taken to drop to whatever the datasheet criteria for ¡°recovered¡± happen to be (10% of the initial value is a common cutoff value). That time is the reverse recovery time.
Your circuit will operate the diode under different conditions. You can scale the results of the datasheet experiment to your conditions. The answer is only logarithmically sensitive to current, though, so it¡¯s not necessary in most cases. You usually just want to know if your diode is fast enough. And that only requires knowing that recovery occurs in a small fraction of the time the diode is supposed to be off.
Sent from my iThing, so please forgive typos and brevity.
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On Mar 9, 2021, at 5:50 PM, jrseattle <jdr@...> wrote:
?Hi, Tom.
I received the UF4004 Ultra fast diodes and replaced the 1N4004 diodes in the circuits loading the secondary of transformer T710 but to no avail. The behavior hasn't changed.
Just curious what the best way of testing the switching speed of diodes is. I used a sine wave generator (into 50 Ohm) to test these diodes (just feed the diode the signal and check the other side but the only difference I see a more attenuation by the 1N4004 diodes, about 15% more. Frequency didn't matter (I went up to 9 Mhz)
What is interesting is that the resulting sine wave is not cut-off at the bottom or top (depending on the orientation of the diode) but has a lower amplitude and is either completely positive or completely negative - but still a sine wave.
Tthe 606A oscillator operates at about 60kHz by the way.
