indulis

I think the more interesting question is how to phase shift each of the gate pulses 120 degrees for each phase!!

Like I said... EMI and EMC are both a little bit of "black magic".

EMI and EMC are both a little bit of "black magic". Why would you say that their ground wires have to be connected together?? What they need is a common reference and that reference doesn't have to be ground. In fact, sometimes it's to your advantage to not have ground at the reference.... it can help with common mode noise in some instances.

I've been designing DC-DC converters for the past 15 years (but I do go back to the days of tape and doughnuts).... if ANY of our CAD designers tried to auto-route one, then they would be looking for work!! Yeah..... I suppose it's industry dependent, and that there are low frequency, low power designs that could get away with auto-route, but DC- DC converters DO NOT, UNDER ANY CIRCUMSTANCES fall into that category!!!!! We were using P-CAD, but have now switched to PADS. All the designs are "intelligent", so net list issues are never a problem and DRC's are layer dependent. A typical 150W quarter brick design is 14 to 16 layers, 3 oz copper on power layers, 2oz CU for signal layers and just about all of them use planar magnetics. As the power densities increase, proximity affects have to be considered more and more... one of the designs I'm currently working on is a 650KHz 1/4 brick, push-pull, current doubler, 1.5V @ 40A SMPS. You just can't put the feedback next to the output traces, it would be suicide..... those have to be guarded and shielded runs!!!! All the power loops HAVE TO BE layed out first..... all the "other stuff" goes into the space leftover. I am not aware of any auto-router that can handle "power design".

One of the inputs to ammeter is connected to "ground". That means you can only measure ground referenced signals, unless of course, the whole thing is floating.

Have you considered a DC solution with one 9VDC source, a 5V regulator and a 555 based voltage doubler? You'll only need the higher voltage when burning the PIC and it range is pretty wide so it wouldn't have to be all that well regulated.

Why select the IRFP150N FET?? It stikes me as being major overkill!!! In a push pull primary, the drain amplitude will never exceed 2 times Vin (plus leakage inductance spikes). With good snubbers, or active clamps, you could get away with 30V MOSFET's that have a sub .01 ohm Rds on. If you think that a bit too close, go to 60V FET's, but unless those FET's (IFRP150N's ) are something you have laying around, your throwing away Rds on for max Vds that you don't need. As long as the primary is switching (with no load on the secondary) you will draw current from your source. Why would you think that you wouldn't?? Even a "powered up" transformer sitting on a bench with an open secondary is consuming some power. Oh........... you didn't say how much current is being drawn??

Your observation, that with half charged batteries, you don't have a problem, might be a clue. The motor winding impedance is fixed, so as your voltage falls, so does the current. Current is directly proportional to flux field strength. Where is the 555 located within the system? Is it some signal the the mower is suppose to detect when it gets to a "perimeter"? MP is correct that the circuits should have "some common" reference point. Since the wheel motor and the blade motor will not always generate the same flux field, so cancelation probably won't work. I can only suggest to minimize exposure of high impedance loops to the field (i.e. keep all wiring as short as possible, make sure the "input" components are as close to the LM393 as possible, make long runs with triaxial, coaxial, twisted shielded pairs or at bare minimum twisted pairs. If you can get you hands on some Mu metal, you could shield your circuit with that!!

Talking in terms of positive and negative voltages is a bit missleading.... talking in terms a potentials isn't because that would apply for all cases... for example, if you had -12V and -24V supplies for a circuit... both NPN's and PNP's could be used, not just PNP's. If I was to say.... to turn a PNP transitor on, you have to "inject" electrons into the base and to turn a NPN transistor on you have to "pull" electrons out of the base..... does anyone think this is not correct?

Measuring AC power isn't as straight forward as measuring DC power. Do you want to measure... real power or apparent power or average power or RMS power or real average power...etc. etc. etc. All of these are different and the cricuitry needed to measure them is different as well.

Yes, "errors" can occur, and happen often with manual routing, but it's the user that defines and sets up the "rules" for DRC..... Different rules can apply for similar situations... for example: A PCB with a .25" hole in it. If you have the hole drilled, the accuracy of the center location is typically +/- .01", but a machined holes center accuracy is +/- .005". So DRC clearances from the hole to copper or board edge would be different. Another example would be copper weight.... with 3oz copper minimum trace width is 8 mils with 8 mil spacing. With 1oz copper I believe that number goes down to 4mils. As a side note... auto routing isn't used very often in analog design, it's more of a digital thing.

A bit more clarification on a few points.............. Gate capacitance isn't the "important" number... "total gate charge" is what will determine how much current is needed to switch a FET on in a particular amount of time given the drain source voltage. Typically, the lowest Rds on is had at the highest Vgs (max channel enhancement), but may not be, and in most cases isn't, the optimum operating point unless it's a static application (i.e. DC switch). Unless prolonged periods of time are spent in the ohmic region, switching losses in a power MOSFET aren't that big when compared to Rds on losses (I^2R). Assuming adequate current is available, optimal gate drive voltage levels will vary with switching frequency.

As far as I know, DRC is used in PCB layout, not schematic capture. The layout and schematic net lists can be compared for differences, although, with an "intelligent" package such as PADS it happens "pretty much" automatically.

This is ONLY true if the impedances are the same.

A ground referenced Ammeter?

Ante Do you by chance have the "chemistry" to support that statment.... I'd love to see it!! Indulis

A 220uH inductor is the same as a .22mH m is 10^-3 and u is 10^-6 and n is 10^-9 and p is 10^-12 Once the chemistry of a lead acid battery is depleted, NO AMOUNT OF ZAPPING WILL BRING IT BACK TO LIFE, PERIOD!!! This is a irrefutable fact... the zapper company just wants to sell you some gadget. The same laws of physics/chemistry that apply to you and me, applies to them. If you can't get back to the batteries original ampacity, nothing has been rejuvinated. Hell, I can take a lead acid battery that has a shorted cell, over charge it and it will work just fine in a car as long as I start and charge it every morning and evening. If this is what you consider "rejuvinated" then yes you are right and it will work. For my money, if you can't get back to the original spec's window, than no rejuvination has taken place.

Check out the battery section on this website..... http://www.golfcarcatalog.com/phpbb2/ When a lead-acid battery is "gone", it is GONE!! No amount of "zapping" is going to bring it back to life... you can't change the laws of physics!!

Here is one way to look at transistors.......... Consider a large, tall water tower with a faucet on the side. For a NPN, the water tower is the collector voltage the faucet handle is the base, and the what comes out of the faucet is the emitter. The more you open the faucet (provide more base current) the more comes out (emitter current). Also, the more you open the faucet the lower the pressure differential between faucet inlet and outlet (lower Vce sat). If the water tower side pressure becomes too high, the faucet will fail (collecter voltage to high and transistor goes up in smoke)... etc. etc.

Two reasons come to mind right away......... 1) base current isn't being limited 2) you have a high emitter current with a high Vce

Voltage ratings on caps relates directly to the dielectric. Temperature rating will follow ESR and ripple current. ESR & ESL will change with frequency.

Voltages "jump"???? While electrons may "jump" from valence to valence, can you please explain the theory of "-ve voltage jumping" from emitter to collector???

Those resistors make sure the MOSFET's turn off. MOSFET input impedance is very high and a slight amount of leakage current could turn them on.

To understand how "they" work, you really need to understand semi-conductor physics including electron bonding at the atomic level. Once you get "that stuff down", terms like... doping levels, majority and minority carriers, etc. will make a bit more sense and you'll know exactly how they work.

The way I learned semi-conductor theory said max output current is determined by input current, not the other way around.