indulis

First, sorry for the typo... my XHR 40-25 is 0-40V, 0-25A not 40A, but hey... 1KW is 1KW. The SMPS in a computer is a discontinious mode flyback. The switching edges all ring like hell and the ripple is a bitch to get down. The reason "they" use this topology is that it's "CHEAP" to build (you get what you pay for). You don't need a output inductor (actually the transformer isn't a transformer at all, it's a coupled inductor, whose secondary "kinda" acts like a ouput inductor) and you don't need a flywheel diode. This saves $$$. The down side is that this is the worst possible topology to use when you want "clean" DC. A forward converter will have ripple levels an order of magnitude lower just for starters and can easily be made even lower with an additional small LC. A computer PSU isn't very compact when you consider DC-DC converters like Vicor's first generation units, back in the mid 80's (VI-200: 4.6" x 2.4" x 0.5" (116,9 x 61,0 x 12,7 mm) and 6.0oz./170g) were up to 50w/cubic inch and some models up to 90% efficient. The computer PSU isn't even close to that power density. In fact, the entire amp, with power supplies could probably be put into the volume of a computer PSU. Like I said, if money isn't an issue, sure you can do it, but an off-line flyback isn't the way. Here's the primary FET and output ripple for a 24V 4.5A DC-DC

Those who work in the industry have probably heard of a company called Vicor. It was founded by a guy named Dr. Patrizio Vinciarelli... When I was working for LTX, I was fortunate enough to have had a working relationship with Patrizio and Vicor when in it was in it's infancy (just a bunch of guy's in a office condo

Thermal conduction and capacity are material related. Thermal "convection" is not. Yes, the copper heat sink will take longer to heat up, but it will reach the same final temperature as the aluminum heatsink

The metal is NOT important!! A heatsink of a particular size, whether it's made of copper or aluminum, IS THE SAME!! Now if you wanted to talk about thermal capacity, that's a different story.

What is the purpose of R1 & R5? I don't think you'll get to far without some sort of stable reference... a pot to Vin will not do it. What is the application? It might help in trying to figure out how best to minimize drift!

It would be worth while for "meter users" to read a few of these App's note's... http://store.cd4power.com/cgi-bin/cd4power.storefront/44ef513100171934271d0c9f89420625/Catalog/1120

I've never built that particular circuit, but have built very similar circuits. Unfortunatly, the easiest way to measure current it to put it through a resistor and measure the drop. You indirectly bring up the age old question of... how good is good enough!! Since there will ALWAYS be "some drift", how "little" is is "little" enough? Better precsion calls for better part's... i.e. a 20 ohm .01% 25PPM resistor would be nice, but is it practical? Same goes for the input offset voltage to the op-amp... how small is small enough? Then there is the reference voltage and the resistive divider... how good is good enough? The better it has to be the more it will cost, and the more complex it'll become. I didn't put any values in, exept the 20 ohms and divider nodal voltages, because they are the key to "operational concept"... 120mA and 20 ohm... Hmmmm that's 2.4V, so varing the voltage across the 20 ohm from 0 to 2.4V gives you 0-120mA. You could get fancy with a SUPER accurate and stable resistor and make a current mirror and have it work for any load within the compliance voltage of your source. How "good" do you need it to be?

http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

The "ampacity" of wire is based on temperature rise. Different types of insulation on the same wire AWG will have different ampacities. It really comes down to how much drop can you tolerate. If you need to be "legal" in the regulatory agencies eyes, there are "tables" that specify allowed levels. As a point of reference, the "fusing current" of 30AWG (bare, solid wire) is 10A.

Why not try something like this...

Check out Philips for the semiconductors, the passive devices you can get almost anywhere.

Does it have to be with Thevenin's? Try it with a "delta-Y" transformation..........

It's a monolithic ceramic disk capacitor.

Be careful here... Yes, it's a boost converter, but by definition, a boost converters output will always be bigger than it's input. Just because it says the input range is to 5V, doesn't mean you can put 5V in and get 3.7V out... won't happen. Your input voltage would have to be less than 3.7V. Also, you don't "have to use" the "on-board" LDO. The internal "switch" is good for 1A, so you can get more than 200mA out of it.

But 1 micro ohm and 100A gives you .1mV. You said you have a mV meter. Seems like a better meter would be an "easier road", than the cost and trouble of constructing a 100A source (these current levels are not easy to deal with). Contact resistance and wire IR drop come into consideration REALLY FAST!!

I don't see NewToElectronics mentioning/asking anywhere about powering a cell phone, but anyway... First, a DC-DC converter works by "chopping" the input DC voltage into a square wave, it's not a "sinusoidal a/c source". There are a few things to consider when doing "this" with a DC-DC converter. The most basic is... does the ouput voltage need to be isolated or not. If not, you don't need a transformer, it can be done with a "buck converter", whose major components are a power switch, feeding a LC filter with a flywheel diode, to keep the current flowing during the power switch off time. You are correct in how the duty cycle is calculated in a "ideal" circuit, but in the real world you have to figure out your losses as those will make your duty cycle a bit larger. That's it... it comes out DC you don't need any additional circuitry.

What do you consider high frequency?

Think of this way... at what frequency will a RC or RL resonate?? That will lead you to your answer....

There isn't anything very "special purpose" about switching diodes, as Audioguru points out in mentioning the 1N914 and 1N4148, which are quite common/generic. Semiconductors in general, that are used at microwave frequencies are COMPLETELY DIFFERNT ANIMALS.

Greetings John at this point voltage has nothing to do with it if the above condition is true. Beside, that "general rule" to which you refer, only applies to a "single" BJT.

One thing that will happen when you use a single 555 as a PWM is that the switching frequency will move around (a lot) when you vary the voltage on the control voltage pin.

A transistors Vce sat voltage is current (Ib & Ic) dependent. For example, with Ic=10A & Ib=3.3A the 2N3055's Vce sat max voltage is 3V, while with a Ic=4A & Ib=400mA, the Vce sat max voltage is 1.1V A darlington transistor will saturate just like any other transistor. The only thing "special" about a darlington is it's high Hfe. When transistors are connected in a "darlington configuration" the Hfe's of the transistors multiply. In fact, darlingtons are very easy to saturate because of it's high Hfe. By definition saturation is when Hfe * Ib > Ic the transistor is then considered to be saturated.

Yes, yes... at a minimum, you have to sample at least twice the frequency your trying to measure... blah, blah, blah. You could sample all day at 1000x the frequency, but unless you know where your starting from, it's worthless. It's still all based on some reference!!! It can only multiply of divide some base clock... how acurate is that??

Yes you can, you have to "off-set" the adj pin lower resistor to -1.2V. Now... how you get the -1.2V is another story. The key is to be able to have the adj pin go to zero.

Of course there is error, the question is how much and does it matter... what's the accuracy of the reference clock?