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I built ESC that had a 1N4007 as flyback diode. It was destroyed because my ESC was working with high PWM frequency. I replaced the 1N4007 with BYV29 ultrafast rectifier diode.

The result was good this diode can support 20 kHz frequency without any overheating.

What is the maximum frequency that this diode can support? How can I calculate it from its datasheet?

winny
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0ussama
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  • I'm not sure it is an easy calculation... What voltages etc. are you working with? If low, then you can use a Schottky instead of an ultrafast, which effectively can handle any frequency an ESC would use. – MadHatter Nov 09 '21 at 00:58
  • @MadHatter Or if high, you can still use a silicon carbide schottky, which are available with voltage ratings up to 3300 volts, and possibly higher--that's just what I've used before. – Hearth Nov 09 '21 at 01:20
  • The calculation will be complicated and might depend on duty cycle, not just frequency--I've not done all the math. The most relevant datasheet parameters would be trr, Qrr, and Irrm. Which all vary quite a lot with temperature and dI/dt, so good luck! – Hearth Nov 09 '21 at 01:22
  • Can you tell us what your load is in volts and amps. It sounds like 1A is not enough. The 1N4007 is normally not good for high frequency. – Gil Nov 09 '21 at 01:25
  • @MadHatter , I am working with 5V , and the MOSFET gate is driven by 12 V (using TLP250 and step up module 5V to 12V). the problem is my motor consume high current (4 A - 7A) ,So i didn't find good one (Schottky) to use as Flyback diode . – 0ussama Nov 09 '21 at 01:27
  • @Gil 5V-7A (MAX) – 0ussama Nov 09 '21 at 01:28
  • @Hearth okey . then i Just want to know approximately if this diode (BYV29) can handle 25 KHz . The good point that prevent me to not change to any other Diode , is that this diode is powerful and can support high frequency at high current consumption . while the others either overheated or fried . – 0ussama Nov 09 '21 at 01:33
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    Your BYV29 has a recovery time of 50nSec. That is 0.125% of a cycle at 25kHz. I think you'll be fine with this diode at 25kHz. – GT Electronics Nov 09 '21 at 01:48
  • I'd rather avoid recirculating through the diodes at all. In such a low voltage application it's much better to drive fully ON the MOS on the recirculating half leg exploiting synchronous switching. RDS(on) gives much lower losses w.r.t. the forward diode drop. In this setup diodes will only work during anti-shootthrought dead band and you may even find them unnecessary and happily live with body diodes alone. – carloc Nov 09 '21 at 06:29

2 Answers2

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As GT Electronics commented on, if the \$t_{rr}\$ if <1% of the period, you're probably safe.

In other advice, a 1N1007 is for 1kV voltages... Given your working voltages of 12V, from an efficiency standpoint, you would be much better with a low voltage Schottky diode. It will have less switching loss due to an effective \$t_{rr}=0\$, and a lower \$V_f\$ so less conduction losses.

Something like Digikey - MBR735

MadHatter
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For a short period of time, whatever current was flowing in the inductor will be flowing in the flyback diode, until it trails off. The diode needs to have at a minimum a peak current rating of your inductive load. The voltage shouldn't need to be rated to much much greater than supply voltage as the diode itself prevents the normal high voltage spike. For a good explanation look at this link: Determine adequate speed of flyback diode for a relay Analog devices published an application note: APPLICATION NOTE 849, this explains how to do the calculations. Here is the link: https://www.maximintegrated.com/en/design/technical-documents/app-notes/8/849.html

Gil
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  • Hi, You mention Analog Devices application note 849, but that seems to be on a different topic ([see here](https://www.analog.com/media/en/technical-documentation/application-notes/AN-849.pdf)). Was that app note number a typo? Can you add a link to the actual document you mean, so there's no confusion? Thanks. – SamGibson Nov 09 '21 at 03:07
  • You also need to consider the diode's turnoff speed. – Hearth Nov 09 '21 at 03:11
  • thank you for your reply – 0ussama Nov 09 '21 at 19:33