Search found 89 matches

by fsdenis
Fri Jul 18, 2003 1:51 pm
Forum: General Discussion
Topic: Small Jameco fall catalog
Replies: 9
Views: 4115

Small Jameco fall catalog

I was shocked to see the shrinkage in the new Jameco catalog. I don't see 6n137's (fast opto- couplers) nor 2n4401's nor 2n4403's any more.<p>Jameco has been a favorite electronics parts supplier for decades.<p>Are we electronics tinkers vanishing in this country, causing market shrinkage?
by fsdenis
Fri Jul 18, 2003 1:15 pm
Forum: General Discussion
Topic: WTB for friend: Cheap 12V 20A supply
Replies: 10
Views: 5834

Re: WTB for friend: Cheap 12V 20A supply

I just use a 12v car battery about 80 amp-hours capacity as a 12v dc power supply.<p>It supplies 20 amps easily for 2 hours or more. Then I just put it on a charger for a while.<p>It is also good for 30 to 90 amps for shorter times and is very quiet -no ripple- compared to electronic supplies operat...
by fsdenis
Tue Jun 10, 2003 7:24 pm
Forum: General Discussion
Topic: 2-axis mirror controller
Replies: 17
Views: 7731

Re: 2-axis mirror controller

You might look into radio controlled servos that go into "toy" cars and airplanes. Available cheaply from Tower Hobbies and others.<p>If you don't want to use a radio for control, It is not hard to design a 555 circuit for local wire connected control. <p>I haven't yet gotten into the smal...
by fsdenis
Tue Jun 10, 2003 7:14 pm
Forum: General Discussion
Topic: most useful books
Replies: 14
Views: 6463

Re: most useful books

Todd: I looked up your circuit. Interesting. Thanks for showing it to me.<p>Transistors in linear mode still fox me. For instance, I can build a stereo amp but I can't get a "feel" for it and must endlessly cut,fit, try and evolve to get it to work.<p>I have been looking for ways to "...
by fsdenis
Mon Jun 09, 2003 12:13 pm
Forum: General Discussion
Topic: most useful books
Replies: 14
Views: 6463

Re: most useful books

Better Phrasing:<p>If we have a current to voltage converter feeding a voltage controlled current regulator and we can control the total gain with choice of two resistors then, It seems to me that we then have a current controlled current regulator.<p>If we then vary the input current to vary the ou...
by fsdenis
Mon Jun 09, 2003 10:32 am
Forum: General Discussion
Topic: most useful books
Replies: 14
Views: 6463

Re: most useful books

I agree with Analogee's judgement that the notion of a bipolar transistor being a current controlled current source is hard to use for engineering purposes. But his statement provoked me to wonder if two of Forrest Mims' opamp circuits might be combined to simulate this mode of bipolar transistor op...
by fsdenis
Mon Jun 02, 2003 6:18 pm
Forum: General Discussion
Topic: most useful books
Replies: 14
Views: 6463

Re: most useful books

In addition to Mims and Lancaster's fine stuff, there are some older books I use frequently.<p>"How to build and use electronic devices without frustration, panic, mountains of money or an engineering degree" by Stuart Hoenig and Leland Payne<p>This written when chip opamps were new and ex...
by fsdenis
Mon Apr 28, 2003 9:00 pm
Forum: General Discussion
Topic: A battery switch and a switching power supply
Replies: 3
Views: 2186

Re: A battery switch and a switching power supply

myp71:<p>I use a nautilus deep cycle 12v battery about the size of a car battery as a high current power supply. This will give you at least two hours of 18 amp operation before the battery voltage drops to 11.5 volts. If you have 120vac 60hz (regular purchased power from the electric company) you c...
by fsdenis
Mon Apr 28, 2003 7:51 pm
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

Chris Smith:<p>Thanks for the fet hints indicating they might not
be as easy to destroy as they were (about 15 years ago) when I last tried them.<p>I, too, have a filing system similar to a black hole. Nothing comes out easily.
by fsdenis
Mon Apr 28, 2003 7:40 pm
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

On my bench, I see that 20 tip41c transistors in parallel with 60 ma Ib for each transistor gives me a total parallel Rce of (max) .2ohms/20.<p>At a total Ic of 35amps, I measure Vce of less than .3volts.<p>And any Ic from 0 to well past 35amps does NOT change or influence total Rce.<p>This ability ...
by fsdenis
Mon Apr 28, 2003 7:23 pm
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

Ron and Russ:<p>Thanks for the clues. <p>I read of unsaturated and saturated operation of bipolar transistors. Perhaps "saturation" has more meanings than base-emitter saturation?<p>On my bench I see three very different modes of operation of the tip41c (and other) transistors. 1) Rce = m1...
by fsdenis
Mon Apr 28, 2003 8:58 am
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

Chriss Smith:<p>Thanks for your comment. Has there been a "b" version of power fets developed similar to CMOS "b"?
by fsdenis
Mon Apr 28, 2003 8:18 am
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

Al Sekeet:<p>Thanks for the suggestions. I've written them down for further study and experiment.<p>The notion of saturation of the base-emitter junction keeps coming up. It seems related to the notion of storage time. I've had a little time for further study and digestion of comments so far. Maybe ...
by fsdenis
Mon Apr 28, 2003 7:51 am
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

RonH:<p>Is there language that makes clear whether one is talking about voltage inversion in an amplifier or about power inverters?
by fsdenis
Mon Apr 28, 2003 7:42 am
Forum: General Discussion
Topic: fast high current transistors
Replies: 27
Views: 11404

Re: fast high current transistors

RonH:<p>You are correct. I am taking output from the emitters and there is no waveform inversion compared to base-emitter voltage.<p>The inversion I meant to indicate is that the current in the one ohm resistor from emitters to neutral 0v between +5v and -5v rails is reversed in direction depending ...