On Sunday, June 17, 2012 03:21:33 AM Jon Elson did opine: > gene heskett wrote: > >> Yes, I put a 1 uF cap on the back of the board directly under the > >> driver chip. One for the > >> low-side driver and logic, one for the floating high-side driver. > >> I've been using this general > >> topology since 2004 or so in my brush servo amp designs. > >> > >> Jon > > > > Sounds like I've got a skuttle, carrying coal to Newcastle. :) > > I used to have 0.1 uF there, which was definitely marginal. When I > upped the size of the > FETs I used, the high-side drivers started cutting out on their > undervoltage trip. Also, the current > pulses drawn when the low-side transistors were turned on caused a dip > in the 12 V > logic rail (I used 4000 CMOS in the brush servo amp) that upset the > sense amp > in the logic-out optocouplers. This quirk took me a long time to find. > Upping a bunch > of caps to 1 uF took care of this. > > Jon
Yup, sometimes I've had to sit and stare at a slew rate limited waveform that is 4x slower than the chip book says it should be for quite a while before it dawns on me to probe the power rails on the chip. That usually has me getting out those teeny little springs that fit right on the end of the probe to use for the ground reference. There are times when the probes normal 5 or 6" ground lead may as well be a hundred yards of antenna. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> Television -- the longest amateur night in history. -- Robert Carson ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
