Re: International standards (2023 Update)

^^^^^^^^^^^^^^ Yup. Use it. It'll work.

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Best Regards,
Mike

BTW, John mentioned that the diodes blocked the discharge.

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Hello all,

A question about fuses:

If a Quick Blow (glass type, 20mm) fuse is rated 250V 1A can I use it to protect a 9v ni-mh battery as well, or will it only blow if the voltage is 250 ?

You can go to places like

or or even Radio Shack.

Look for an item called Standoffs. The come in different lengths and materials. Thoses are the little spacers your looking for that go between the chassis and your motherboard. You can get them in Brass, Aluminum, Nylon.... and different thread sizes.

Almost every town I've ever lived in has a sheet metal shop somewhere. They can bend and cut sheet metal for you and generally pretty cheap. Most do not have the dies to cut the holes for computer connectors like the DB9 or DB25 but you can do that by using a drill then using a notcher.

Sorry but that is about all the help I can provide. Have fun and try to keep the cut fingers to a minimum.

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I am seeking a textbook covering opto-electronics design. I am building various optical communications circuits using documents such as those on the Maxim-ic web site, however I feel the need for a more thorough understanding. I have read a pile of books on fiberoptic theory, and communications theory however I cannot locate anything covering applied basics for signal modulation, laser drivers, clock-retiming &c.

Any help appreciated, Fritz

rather than conect the capacitor to ground u cld make use of the miller efect and conect it from gate to drain. this wld make any delay much more related to diming rather then delay before starting to turn off. basicaly the miler efect multiplies the efective capacitance by the gain of the circuit, wich is probably 30 or more at a very wild gues, its basicaly gm x r load. wich both vary with curent.

Colin =^.^=

Since you state DC current, and high voltage isolation, ther are two solution types:

1) Hall effect transducer. These can do the job, but one cannot get 1% accuracy, linearity or temperature insensitivity that you seem to demand. But if you are willing to put up with about 12% nonlinearity with isolationof 5nA at 2000V, look at the Zetex ZMC20 (need to modify magnetic coupling to allow 100A sensing). 2) Current transformer (fluxgate) as made by LEM. Expensive, but gives wideband and precision response. Perhaps you could "roll your own".

Without some calculation or a simulation, I can't say. The reduction ratio is approximately equal to the voltage gain around the control loop at the ripple frequency. This one is simple enough to easily be put into LTspice with an input consisting of an AC ripple voltage riding on a DC bias.

You can download a free copy of LTspice at:

Sorry, I didn't take the time to think through how that circuit works.

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John Popelish

Are you saying I could attach a 1 Farad capacitor to the chip and not overload the output???

My first attempt was simply connecting a big resistor from gate to ground with no cap. But that gave almost instant turn-off, even when using a 10M resistor! That was why I removed it and used a cap instead. But I think I can now see that if I use a resistor and a bigger cap then it will ramp the voltage down more slowly.

Colin can you please explain the Miller effect a bit more. And are you saying a cap from gate to drain (which is sitting at 40V) plus also the resistor to ground?

PS. See also my separate posting "Peak current to charge a capacitor". I was also concerned that adding too big a cap to the chip outputs might overload them when the cap is charging. How big a cap is too big?

Yup. Or even a short to ground.

John

Here is a current (excuse the pun) article on the subject:

I haven't analyzed it, but I think it may be necessary for stability. Without it, the opamp looks like it would be driving a capacitive load.

--
local optimization seldom leads to global optimization

my e-mail address is:   AT mmm DOT com

Those specs that define max load capacitance apply to a faster digital output where the cap is constantly being charged and discarged. Also, if you try to drive a big cap it takes longer to charge it up with a limited charging current.

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Best Regards,
Mike

Sure. The gate cap is so small that you won't notice an increase in turn off time because it's down there in the uS range.

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Best Regards,
Mike

It doesn't care about the voltage. It'll blow if something manages to draw more than an amp (or close to it - fuses are pretty accurate, but I doubt that one has ever been made that's *EXACT*) through it at anywhere from a voltge that's barely measurable, on up through 250 volts (And beyond, but read on) The 250 rating is all about "When this puppy blows, there's gonna be an arc that we don't want hitting anything else - This fuse is designed to soak up, contain, or otherwise safely handle the arc that a 250 volt source would produce." Which means that for a 9 volt application, the "anti-arc" capability is overkill. It won't do any harm, but it's "wasted effort", in a manner of speaking. Particularly if you can get a 1 amp, closer-to-9-volts fuse for lower cost. (Not that the cost of the fuse means much in a one-off situation like yours, but even a penny difference in the cost of a part can make a significant difference when talking about a production run of who-knows-how-many-million units)

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Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
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Screw the BP and notch approach. Usee a HP filter and set the cutoff freq well above say, 150 Hx just in case. There's bound to be equipment around with rectifiers in it that will produce harmonics that will get back into the power lines and radiate. IME, in a 60 Hz system, I'll find plenty of 120 Hz noise. I can filter it out and still pass a 100 Hz signal, though.

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Best Regards,
Mike

You've got me puzzled. That circuit looks like a simple square wave oscillator. Its duty cycle will therefore be roughly fixed. Yet you say you can vary the speed of the motor? That's what the author claims for his 'Pulse Width Modulation' circuit too. Surely, PWM keeps the cycle period (and hence frequency) fixed, while changing the duty cycle? adrift somewhere. Can someone clarify please?

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To build it, I'd use perfboard, with copper strips. The holes for the MOSFET, and for the heavyish duty wires to the motor, will probably need drilling out slightly (to maybe 1 mm). Use a 14-pin DIL socket for the 4011. Drill holes in two corners of the small board if you want to mount it in a small case. Alternatively, with such a compact, light board, a piece of sponge will secure it adequately. A hole in the case will accommodate your pot.

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Terry Pinnell
Hobbyist, West Sussex, UK