Search found 71 matches

by rosborne
Tue Sep 14, 2004 3:43 am
Forum: General Discussion
Topic: Transistor Relay Drivers
Replies: 12
Views: 1931

Re: Transistor Relay Drivers

Thanks Stephen, I'm still a little confused by the Vth, but I think I get the split resistor thing now. I think your saying that the low impedance the Capacitor would see makes for a very small time constant, so we need to use the split resistance to slow down the discharge of the cap. Right? Lookin...
by rosborne
Mon Sep 13, 2004 12:55 pm
Forum: General Discussion
Topic: Transistor Relay Drivers
Replies: 12
Views: 1931

Re: Transistor Relay Drivers

jwax,
I see Vgs = 4 volts on figure 5 on this spec as 0 Amps regardless of Vds.MOSFETspec
I don't use MOSFET regularly so I could be wrong, but the threshold voltage doesn't look like full on to me. I guess I'm missing something. :/
-Rick
by rosborne
Mon Sep 13, 2004 5:19 am
Forum: General Discussion
Topic: Transistor Relay Drivers
Replies: 12
Views: 1931

Re: Transistor Relay Drivers

In reverse order:<p>Hello, I don't think a Darlington is needed in this case I only need a ß of about 1.5.<p>JWAX, I don't think the Theshold Voltage turns a MOSFET on, it brings it to the threshold of on. In order to use an enhancement MOSFET and to open the channel Vs = 24, Vd = 0. I'm guessing I ...
by rosborne
Fri Sep 10, 2004 12:33 pm
Forum: General Discussion
Topic: Transistor Relay Drivers
Replies: 12
Views: 1931

Transistor Relay Drivers

Are there any hazards associated with using a transistor to drive a 24VDC(coil) relay? Should I put a cap at the base to stop noise from activating my Relay? It seems like I should to me. Any thoughts?
-Rick
by rosborne
Thu Aug 26, 2004 2:28 pm
Forum: General Discussion
Topic: A watts question.
Replies: 6
Views: 1267

Re: A watts question.

Should be 'joules as energy' not 'joules and energy'.
by rosborne
Thu Aug 26, 2004 2:20 pm
Forum: General Discussion
Topic: A watts question.
Replies: 6
Views: 1267

Re: A watts question.

I think of watts as Power and joules and energy. One interesting conversion is 1 horsepower = 746 Watts = 550 ft*lbs/sec. A watt can be thought of as energy spent over time which makes the watt-hour confusing, for me anyway. Serway says, "Power is defined as the time rate of energy transfer." 1 watt...
by rosborne
Thu Aug 26, 2004 10:18 am
Forum: General Discussion
Topic: Current source
Replies: 64
Views: 11763

Re: Current source

Me, too.
-Rick
by rosborne
Tue Aug 24, 2004 3:36 am
Forum: General Discussion
Topic: Offset voltage on voltage follower
Replies: 19
Views: 3748

Re: Offset voltage on voltage follower

Stephen,<p>I like it. Much more elegant solution than my flailing produced. :) The buffered output circuit looks better to me though, in case the instrument turbo describes is an active load. He has the OPAMP, it would be a shame not to use it and the test circuit with the 1k load would work, too. -...
by rosborne
Mon Aug 23, 2004 2:04 pm
Forum: General Discussion
Topic: Offset voltage on voltage follower
Replies: 19
Views: 3748

Re: Offset voltage on voltage follower

Ok, got it down to 6 resistors and one opamp if you have the plus and minus 5VDC sources. The general idea is the same as before. . . voltage divide the signal down to 3/5. Divide the -5VDC source to -0.5 and configure OPAMP as a difference amplifier with all of the resistors equal to 10k. I can sen...
by rosborne
Mon Aug 23, 2004 1:39 pm
Forum: General Discussion
Topic: Offset voltage on voltage follower
Replies: 19
Views: 3748

Re: Offset voltage on voltage follower

I still think an adder will work. 1. voltage divide your dc source to 0.5 volts. If 5 VDC source 9k and 1k resistors. 2. voltage divide your 0-5 volts source down to 0-3 with a 2k and a 3k resistor. 3. add the two voltages for a 0.5 to 3.5 VDC output signal that track linearly with the 0-5 volt sour...
by rosborne
Fri Aug 20, 2004 5:58 am
Forum: General Discussion
Topic: Offset voltage on voltage follower
Replies: 19
Views: 3748

Re: Offset voltage on voltage follower

Have you considered:
A 3/5 voltage divider for your 0-5 volt signal. Hoping for a 0-3 volt output.
Divide your DC voltage down to 0.5 VDC.
Then taking those two inputs into an OPAMP configured as an adder to get 0-3.5VDC out?
7 resistors and an OPAMP.
Would that work?
-Rick
by rosborne
Wed Aug 18, 2004 4:22 am
Forum: General Discussion
Topic: Current source
Replies: 64
Views: 11763

Re: Current source

Engineer, I think that might work, but I'd still like to avoid use of a pot.<p>Dale, Don't forget that alpha is beta dependent. α = ß/(ß+1) and the input of the current amplifier is the base the output of which is on the collector or emitter (Ic and Ie are nearly equal because as you pointed out α ~...
by rosborne
Tue Aug 17, 2004 1:21 pm
Forum: General Discussion
Topic: Current source
Replies: 64
Views: 11763

Re: Current source

I figured it out a different way, but am still interested in other ideas.
-Rick
by rosborne
Tue Aug 17, 2004 12:48 pm
Forum: General Discussion
Topic: Engineering Mathematics
Replies: 5
Views: 970

Re: Engineering Mathematics

My sympathies, the book I studied that stuff out of was called 'Complex Variables with Applications' by A. David Wunsch and it was the hardest class I ever took. The only advice I can offer is study hard, don't give up, work problems, work more problems and it will soon be over after you've worked e...
by rosborne
Tue Aug 17, 2004 12:37 pm
Forum: General Discussion
Topic: Current source
Replies: 64
Views: 11763

Re: Current source

toejam, I don't think that will work. I need to smoothly change the output current from 0-250mA with a control input of 0-10 volts (the source of the 0-10 volts input can handle maybe 30mA max). I think the lm117 device would give me whatever current the load demands while maintaining a constant vol...