On Wednesday 15 May 2013 14:12:02 Peter C. Wallace did opine: > On Wed, 15 May 2013, Gene Heskett wrote: > > Date: Wed, 15 May 2013 11:40:09 -0400 > > From: Gene Heskett <[email protected]> > > Reply-To: "Enhanced Machine Controller (EMC)" > > > > <[email protected]> > > > > To: [email protected] > > Subject: Re: [Emc-users] Superglue, or Loc-tite for that motors > > flywheel? > > > > On Wednesday 15 May 2013 11:24:49 John Kasunich did opine: > >> The current in that design is very dependent on transistor parameters > >> such as beta and Vbe that will change from part to part and with > >> temperature. Adding emitter resistor(s) stabilizes things. > >> > >> On Tue, May 14, 2013, at 10:39 PM, Przemek Klosowski wrote: > >>> On Tue, May 14, 2013 at 3:08 PM, Gene Heskett <[email protected]> > > > > wrote: > >>>> So it looks like I need to design a 10 amp constant current load, > >>>> switch mode of course. > >>> > >>> Perhaps something simpler? I have a sinking feeling that the > >>> electronics wizards will soon hand me my head on the platter but I > >>> think that the following circuit might work as a current load: it > >>> sets up a lousy voltage reference and uses it to trickle enough > >>> current into the base of a Darlington pair to drive the desired > >>> current through the load. > >>> -------------------------------------------------------------------- > >>> - --------- > > > > That PNG you sent has the sense R in the wrong leg of the transistor > > John, it should be in the emitter leg. > > > > Anyway, I just stumbled over some 400 volt, 15 amp darlington's at > > Jameco & I will build one bias circuit, feed two of those in parallel > > but with separate emitter R's in the .2 ohm range, $15 and change for > > 5 pieces by USPS first class. I looked at the heat sinks that had > > bugs on them, but they were 30 amp 45 volt PNP Germanium's, of little > > or no use here. > > > > I figure 2 of them sharing a heat sink about 5.5x10 x 2" tall, ought > > to handle that till the cows come home dripping. > > > > That heat sink also has a 6 pack of 1N3210 diodes on it, 15 amp 150 > > volt in a DO5 case, should make a nice bridge so this works in > > reverse too. ;-) > > > > Many thanks for the ideas everybody. > > > > Cheers, Gene > > > > ---------------------------------------------------------------------- > > -------- AlienVault Unified Security Management (USM) platform > > delivers complete security visibility with the essential security > > capabilities. Easily and efficiently configure, manage, and operate > > all of your security controls from a single console and one unified > > framework. Download a free trial. http://p.sf.net/sfu/alienvault_d2d > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > When using bipolar transistors as high power current sinks, make sure > you are not violating their secondary breakdown specs (a lot easier to > kill than you might think) > > > Peter Wallace > Mesa Electronics
BTDT Peter, and FWIW, its just as true when trying to use a HEXFET as an analog control. Internally, it fails open, microchip by microchip until it has no transconductance left. The gate may or may not show any leakage. Which is why I ordered a 5 pack of those 400 volt 15 amp darlingtons, they will get paralleled until the SOAR ratings are inside the curve. 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> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> SCCS, the source motel! Programs check in and never check out! -- Ken Thompson A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ AlienVault Unified Security Management (USM) platform delivers complete security visibility with the essential security capabilities. Easily and efficiently configure, manage, and operate all of your security controls from a single console and one unified framework. Download a free trial. http://p.sf.net/sfu/alienvault_d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
