The IRF820 worked fine at one time, so I don't think I need a lower on resistance.
----- Original Message ----- To: "Multiple recipients of list CHIPDIR-L" <[EMAIL PROTECTED]> Sent: Sunday, November 16, 2003 11:19 AM > The IRF840 has like 0.85 ohms of resistance, an SCR has nearly 0 ohms, you > could > try and use an IRFP450 (IRFP250 (0,075 ohms works even better if resists > the voltages), if it however fit's in there, the IFRP450 has only 0.4 ohms > ON-resistance, there better ones too, You may be able to replace the two > IRF840 with one IRFP450, which will reduce input capacity quiet a bit, this > might give you better pulses, anyway, you may check if your driver circuit > is capable of driving the FET's fast enough into saturation. > > Just some thoughts > > Friedel > > > At 05:14 16/11/03 -0800, you wrote: > >Naw, there are only two and I replaced em both. One of the 820s was > >shorted, but so was just about everything else in the tool (it is an oil > >well logging tool). They dump a high voltage pulse from an inductor into a > >ultrasonic magnorestrictive transducer at 20 cps. I don't seem to have > >enough trigger pulse to make em work. Would the 820 be more sensitive than > >the 840 with regard to the trigger pulse? Most of these type tools use an > >SCR; this is my first experience with a mosfet fired transmitter. > > > >----- Original Message ----- > >To: "Multiple recipients of list CHIPDIR-L" <[EMAIL PROTECTED]> > >Sent: Sunday, November 16, 2003 6:04 AM > > > > > > > On Sun, Nov 16, 2003 at 01:49:19AM -0800, Syd Levine (AnaLog) > > > enlightened us thusly > > > > I just replaced two IRF820 mosfets with IRF840 mosfets. The 820s were > > > > bad, but the device still won't work. Should the 840 work OK in place > > > > of the 820, or have I created a new problem with the substitution? > > > > > > > > > You're fine unless they are sharing current with other irf820s, in which > > > case they will hog it. They have similar voltage specs, but lower > > > resistance and hence higher current. > > > > > > > > > They need about 10V on the gate if you're switching. How were the 820s > > > bad? That will point you to your problem. > > > -- > > > > > > With best Regards, > > > > > > > > > Declan Moriarty. > > > -- > > > Author: Declan Moriarty > > > INET: [EMAIL PROTECTED] > > > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > > > San Diego, California -- Mailing list and web hosting services > > > --------------------------------------------------------------------- > > > To REMOVE yourself from this mailing list, send an E-Mail message > > > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > > > the message BODY, include a line containing: UNSUB CHIPDIR-L > > > (or the name of mailing list you want to be removed from). You may > > > also send the HELP command for other information (like subscribing). > > > > > > > > >-- > >Author: Syd Levine \(AnaLog\) > > INET: [EMAIL PROTECTED] > > > >Fat City Network Services -- 858-538-5051 http://www.fatcity.com > >San Diego, California -- Mailing list and web hosting services > >--------------------------------------------------------------------- > >To REMOVE yourself from this mailing list, send an E-Mail message > >to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > >the message BODY, include a line containing: UNSUB CHIPDIR-L > >(or the name of mailing list you want to be removed from). You may > >also send the HELP command for other information (like subscribing). > > -- > Author: Friedel Bruening > INET: [EMAIL PROTECTED] > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > -- Author: Syd Levine \(AnaLog\) INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
