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Title: ARRL Handbook power supply GOOF Post by: W4AMV on December 28, 2011, 09:31:53 PM FYI, and for more than a decade, a popular PS in the ARRL Hdbk, say 2000 edition, a 28 V @ 10 A has a goof. The crowbar ckt as shown does not work. The MC3423P OVP IC is biased from a 12 V Zener via a 4.7 k series R. Trying to fire an SCR, the Zener falls out and the circuit fails. Change the series R to the Zener to 820 ohm. All is then bliss. This had me going for awhile in trying to wrap up this supply. :D
Title: Re: ARRL Handbook power supply GOOF Post by: WA1GFZ on December 28, 2011, 10:02:09 PM Wow that is a pretty high value. It would take some real over voltage to latch the SCR.
Title: Re: ARRL Handbook power supply GOOF Post by: Pete, WA2CWA on December 28, 2011, 10:48:50 PM Did you check the Handbook Errata section here: http://www.arrl.org/arrl-handbook-reference
I would also send an e-mail to the Handbook editor with your findings. Title: Re: ARRL Handbook power supply GOOF Post by: W4AMV on December 29, 2011, 10:47:49 AM Good idea. Nope, so it is not part of the errata list. So the contact for errata items by the way is:sford@arrl.com
Thanks! Title: Re: ARRL Handbook power supply GOOF Post by: k4kyv on December 29, 2011, 06:45:30 PM FYI, and for more than a decade, a popular PS in the ARRL Hdbk, say 2000 edition, a 28 V @ 10 A has a goof. The crowbar ckt as shown does not work. The MC3423P OVP IC is biased from a 12 V Zener via a 4.7 k series R. Trying to fire an SCR, the Zener falls out and the circuit fails. Change the series R to the Zener to 820 ohm. All is then bliss. Quote Nope, so it is not part of the errata list. So the contact for errata items by the way is:sford@arrl.com Goes to show how few hams actually try to build the construction projects described in the Handbook. After a whole decade, no-one had called attention to the error. Title: Re: ARRL Handbook power supply GOOF Post by: WQ9E on December 29, 2011, 07:41:34 PM Probably a few built it but hopefully nobody experienced a shorted pass transistor and thus discovered too late that the crowbar didn't work.
I wonder if a drafting error crept in before it made it to print? One would hope the original designer tested the protection circuit. Title: Re: ARRL Handbook power supply GOOF Post by: KM1H on December 29, 2011, 07:52:16 PM What does the IC's spec sheet show? Maybe a 470?
Carl Title: Re: ARRL Handbook power supply GOOF Post by: wb6kwt on December 30, 2011, 09:23:32 AM Wow, thanks for the info, I'm building that power supply now, just need to find a case to put it in.
Bob wb6kwt Title: Re: ARRL Handbook power supply GOOF Post by: W4AMV on December 30, 2011, 10:06:56 AM Yep! That supply is FB. However, that crowabr if you ever need it, WILL NOT WORK! Sure enough, if you go to the data sheet for the MOTO (ON Semi) and look at the MC3423 data sheet, page 3- Figure 5, see the equation on the right hand side for RS: Rs=(Vs-10)/(25) k OHM. So they actually add about 15 mA overhead to the Zener current for the IC and the gate current for the SCR. So, in the case of the 12 V Zener and operation of the 3423 IC at 12 V, we need (33-12)/(25) or 840 ohms. I used 820 and the supply in my case tops out at 33 V. Your case may differ. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Good luck, 73 Alan :) |