Diode identification?
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From: Eeyore on 3 Mar 2007 12:18 YD wrote: > Dunno why the 1 uF cap. German overkill engineering ! Graham
From: Phil Hobbs on 3 Mar 2007 14:00 Dave Platt wrote: >> flywheeling diode and a 1N4007 would do the job just fine. Does the FET >> source go to ground ? Many power MOSFETS have a diode internally in that >> orientation across from the source to the drain. It gets there as an >> integral side effect of the manufacturing process. > > Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED > or HiperFRED) for MOSFET flyback protection. 1N4007s aren't > particularly fast, and reverse-conduction losses can be significant if > the switching frequency is high (in e.g. an SMPS). That's probably not > all that much of an issue in a solenoid driver, though. > 1N4007s can take a long time to turn _on_ as well as off. You can get several volts of overshoot in some applications. Definitely not your ideal catch diode. Cheers, Phil Hobbs
From: Arfa Daily on 3 Mar 2007 18:59 "Phil Hobbs" <pcdh(a)SpamMeSenseless.pergamos.net> wrote in message news:45E9C5D0.9080909(a)SpamMeSenseless.pergamos.net... > Dave Platt wrote: >>> flywheeling diode and a 1N4007 would do the job just fine. Does the FET >>> source go to ground ? Many power MOSFETS have a diode internally in that >>> orientation across from the source to the drain. It gets there as an >>> integral side effect of the manufacturing process. >> >> Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED >> or HiperFRED) for MOSFET flyback protection. 1N4007s aren't >> particularly fast, and reverse-conduction losses can be significant if >> the switching frequency is high (in e.g. an SMPS). That's probably not >> all that much of an issue in a solenoid driver, though. >> > > 1N4007s can take a long time to turn _on_ as well as off. You can get > several volts of overshoot in some applications. Definitely not your > ideal catch diode. > > Cheers, > > Phil Hobbs But one that is used by manufacturers world wide for exactly that purpose .... Arfa
From: Terry Given on 3 Mar 2007 23:58 Arfa Daily wrote: > "Phil Hobbs" <pcdh(a)SpamMeSenseless.pergamos.net> wrote in message > news:45E9C5D0.9080909(a)SpamMeSenseless.pergamos.net... > >>Dave Platt wrote: >> >>>>flywheeling diode and a 1N4007 would do the job just fine. Does the FET >>>>source go to ground ? Many power MOSFETS have a diode internally in that >>>>orientation across from the source to the drain. It gets there as an >>>>integral side effect of the manufacturing process. >>> >>>Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED >>>or HiperFRED) for MOSFET flyback protection. 1N4007s aren't >>>particularly fast, and reverse-conduction losses can be significant if >>>the switching frequency is high (in e.g. an SMPS). That's probably not >>>all that much of an issue in a solenoid driver, though. >>> >> >>1N4007s can take a long time to turn _on_ as well as off. You can get >>several volts of overshoot in some applications. Definitely not your >>ideal catch diode. >> >>Cheers, >> >>Phil Hobbs > > > But one that is used by manufacturers world wide for exactly that purpose > ... > > Arfa so? just because it gets used doesnt mean its suited for the task. think bell curve.... BTW in that position its probably a 47V zener, clamping the peak drain voltage. Cheers Terry
From: John E. on 4 Mar 2007 04:40
Terry Given sez: > BTW in that position its probably a 47V zener, clamping the peak drain > voltage. I'd been turning over in my mind that this is indeed a zener, not simply a "plain" rectifier. It is indeed a 47 volt zener. Why was this diode chosen in the design? I'm familiar with the standard diode being used to short-circuit the back-EMF from the solenoid, but I can't figure out the purpose of a zener used in this location. Vdd /\ | | SS SS Solenoid SS | +-----+ | | | | BUZ72 | /---/ ZY47 FET |--+ /\ Diode -------| | |--+ | | | \ | 0.27R / | \ | | | | | /// /// I think that should show proper in Courier or Monaco... or Paris (c: I must add that Vdd is *reported* to be 42vdc. I was handed this board with scribbled specs. May be higher or lower or in a parallel universe. Thanks, -- John English |