indulis

It is my understanding that the spike that is generated during starting is as a result of turning the starter motor off... after all, you are "unloading" an inductive circuit (the motor plus the inductance of the wire to and from the battery to the motor). To size the resistor properly, you need to figure out what would be a reasonable number of times to try starting the motor, and then calculate the RMS value of the spike... yes, the 10W resistor and 2W diode would/will work, but they are also overkill.

The step up method would primarily determine size and weight, but no matter how you get there, you still have to get the voltage back to 50/60Hz to run household items!!

Look at http://www.national.com/ds/LM/LM138.pdf The old data books had a much better write-up, but there is a schematic for a 12V charger near the end. I have built a 40A and 5A version of this circuit and both have worked very well for over 20 years!!

If I had to guess, I'd say because of the process used. For example, in the not to distant past, is was almost impossible to get a buck controller that could do 24Vin and 12Vout without all kinds of level shifting circuits. Lot's of PWM's didn't have a problem with the input voltage range, but with the voltage that could be applied to the feedback amp. A lot of them used a 6V process for that part of the die, although Linear Technologies had a few neat tricks to get around that limitation on certain chips.

Vcc for the LM 311 is 6V, so it's output and base drive voltage will be some level less than that. All that is needed is a series base resistor to limit the current and drop the voltage. The function of Q3 is that of a switch.... it want's to be either hard on, or hard off. A MOSFET, almost always, is a better "switch" than a bipolar. A logic level MOSFET would be the best choice because it is hard on with "logic level signals" i.e. 5V. The down side of logic level FET's is they have a higher "total gate charge" to get the nice low Rds on numbers.... sub .01 ohm FET's are VERY common nowadays. The higher gate charge means more losses due to the switching element (Q3 in this case). Anything that draws power from the 6V source that isn't needed in the circuit to make it function will degrade efficiency.

I think your gonna find it very hard to find a PWM that works with a Vcc of 1.5V

That is correct, R17 is acting as a load. R14, R16 and R18 aren't needed. The LM311 isn't a open collector comparator. I'd use a logic level MOSFET for Q3 and a schotty for D10. Also, the values of L10 and C10 seem disproportionate. It looks as if the schematic is from a simulation program. Some of those components might be needed to make the thing run in the simulator.

Your schematic is of a boost converter running open loop. The duty cycle of your generator connected to pin 3 of the LM311 will control the output voltage. When Q3 turns on, you have in essence placed a voltage step across and inductor. The current will start to linearly ramp up until the transistor turns off. During this, on time, D10 is back biased and all the energy being delivered to the load is coming from C10. When the transistor turns off, the flux collapses, the voltage across the inductor reverses, and the inductor current now starts to ramp down as you draw energy out of it. The output voltage in a boost converter is ALWAYS larger than its input voltage, so the output will be the input voltage plus the voltage across the inductor. There are of course limits to the way you run this converter… you have to consider the switching frequency, the duty cycle and the saturation current of the inductor. For example… if the switching frequency is really low and the duty cycle is high, the inductor could saturate, at which point it stops being an inductor, and you can say bye-bye to Q3 because there is nothing to limit the current.

Typically they are used as jumpers on PCB's when cost has to be cheap, as in single sided or no thru plated holes. To put "ampacity" into perspective, it takes 10 amps to fuse a 30AWG wire.

As you say, those values are "typical". If you had 1mA of collector current and you saturated the transistor, the Vce sat voltage would be VERY different if you had 10A flowing instead. The Vbe will also change depending ion the base current. Vbe also changes with temperature 2mV/

At what frequency did you calculate the capacitive reactance? You are aware that triangular waves are a bunch of sine waves at different harmonic frequencies and amplitudes summed together, right (a.k.a. Fourier Analysis)? Phase shift only pertains to voltage in relation to current or vise versa. Voltage or current by themselves don't have any phase shift. Recall "ELI the ICE man" voltage (E) leads current (I)in a Inductor (L) and Current (I) leads Voltage (E) in a capacitor © by 90 degrees. Or if you preffer, current (I) lags voltage (E) in an inductor (L)... etc.

Without the ferrite properties, you would have to wind it and measure it. Calculation with length, diameter and layers will do very little for something other than a air core inductor. Do you know the inductance factor of the core?

And don't forget about a "driven guard" and don't connect both ends of the shield drain wires in certain app's where EMI/RFI could be an issue, only connect one end.

There is plenty of information out there on buck converters. Check out http://www.linear.com/index.jsp they even have a cad program you can download to help you with your design. As for cap's on the output of a SMPS… you have to be careful! First, if the ESR is to low, the zero in the transfer function caused by the output cap and it's ESR can cause stability problems. Sometimes, you have to put a "crappy" cap on the output in order to stabilize it, or really slow down the feedback loop which would make transient response worse (not good with motors because of start-up currents). Second, the value of the cap has a LOT to do with the switching frequency. The higher the frequency, the smaller the cap. There is plenty of information out there on buck converters. Check out http://www.linear.com/index.jsp they even have a cad program you can download to help you with your design. As for cap's on the output of a SMPS… you have to be careful! First, if the ESR is two low, the zero in the transfer function due to the output cap and it's ESR can cause stability problems. Sometimes, you have to put a "crappy" cap on the output in order to stabilize it. Second, the value of the cap has a LOT to do with the switching frequency. The higher the frequency, the smaller the cap.

There is a TON of stuff on the internet about bode plots… In a nutshell, the bode plot shows you the gain and phase relationship between an input and an output. It can be used to determine stability. As a real world example, bode plots are used to check for stability in SMPS feedback loops. While transient load test can only give a partial indicator as to the loop stability, a bode plot will give you the whole story. For a power supply, you would like to see a minimum of 45 degrees phase margin, a cross over slope of –1 and 20dB of gain margin. Less than 30 degrees of phase margin at crossover is asking for trouble and the unit is probably conditionally stable may oscillate.

This uses a push-pull topology, so only one half of the primary is active at any point in time. Each half winding has 12V across it relative to the center-tap. Through flyback action, the opposite winding end will have 2 times the input voltage when the switching element on side that's being measured is switched off. This is the reason push-pull primary switching elements have to have a voltage rating of at least 2X Vin. If your measuring 24VAC, your measuring from gnd to one end of the transformer primary winding.

I do believe you have that backwards............ LED's (traditional colors) in "modern" times have seen a reduction in current, not the other way around.

You have to be careful with LED's nowadays..... the old rule of thumb doesn't apply across the board anymore. For example, the TLLG/R/Y540 LED from Vishay is spec'ed with a current of 2mA and has a max forward current of 7mA.

I'm confused... Right off the bat I'll say audio is not my thing, but I am very familiar with things in the analog world. In a "first order" DC analysis of the circuit, R3, R4, R11 and R12 do nothing, as one input to all the op-amps is hard tied to ground, and the other is at a "virtual ground" of sorts. Aside from the input offset voltage, there is no voltage potential across any of those resistors, and the additional current the op-amp would have to source or sink due to these resistors is a few orders of magnitude smaller than the normal current flowing. So, my question is this, what exactly do they do from an audio perspective??? What is the math behind the phenomena, as it doesn't figure into the DC gain equation?? As a general observation, in the analog instrumentation world, none of those op-amp inputs would be tied directly to ground. In that particular configuration, they would be connected to ground thru a resistor that is equal in value to the parallel equivalent of all the resistors connected to the op-amp minus input node.

The TL072 is only 13V/µS, that's not exactly fast when compared to the 250V/µS of the AD843 mentioned earlier. A 100µF bypass cap on a opamp that's only capable of a few mA of output current is overkill. For small signal stuff, even more than an order of magnitude above audio, doesn't need anything that big. If the opamp were to draw some current, that would be a different story!! Parasitic inductance is about 2nH/inch, so you would need a LONG run before it became a factor. Yes, when it comes to power, short and fat is GOOD, but it depends on how much current is flowing!!

I can't quite agree with the "over simplification" of the transformer in terms of how much DC current will flow. If the primary is switched at such a frequency that the core never saturates, there is no DC current. The primary current waveform is the familiar ramp on a step (trapezoidal). The step amplitude is the secondary DC current reflected to the primary and the ramp is the reflected inductor current plus the primary magnetization current. Yes, equivalent DC and DCrms currents can be calculated, but they are not a steady DC level.

I'm no expert when it comes to audio, but I do know a bit about op-amps. Audio is a very personal thing.... somethings sounds good to one person, while the next person thinks it sounds bad/flawed. Whenever I buy audio gear, I go into the sound room, close my eyes, and tell the salesman to "show-me-what-you-got". I let my ears tell me what is good and bad, TO ME, not my wallet. Sure, I'd love a Crown pre-amp and a couple of Macintosh tube amp's but THAT JUST AIN'T GONNA HAPPEN. In the 70's, music was played LOUD, and I'm sure that to some degree that has affected my hearing, so my Yamaha reciever and Klipsch Heresy II's do just fine..... spending more would just be a waste as I wouldn't be able to hear the "better performance"!!! Back to op-amps......... the transfer function doesn't do anything more than defign the gain. When reduced to the standard form, the numerator contains, zeros, or points where there is an increase in gain (phase lead), and the denominator has poles which are points where there is a decrease in gain (phase lag). Crossover frequency and phase magin determine stability. A higher cross over frquency means better transient response. Remember also, there are two parts to transient response... one being recovery time and the other being deviation. Gain will control deviation and cross over will determine recovery time. How these parameters relate to how we hear things, I don't have a clue. Now, why would you even consider using a AD843 for audio? It has a full power bandwidth of 3.9MHz and a slew rate of 250V/uS...... seem's like OVERKILL for a audio app's, even if you can hear beyond 20KHz!!! Yes, the "numbers" would be impressive, but how many could actually hear the difference. In the end, how many zeros beyond the decimal place really matter!!

What aspect of aviation

By definition, a Root Mean Square (RMS) voltage gives the same heating effect as a DC voltage of the same value. In the case of a square wave, the RMS value is: Vrms=Vpk*Sqrt(Ton/period) Ton/period is also the duty cycle.

What your trying to do is possible, but not easy. The transformer type is unimportant as long as you remain within its limitations. Oh..... I forgot to mention, what your trying to build here is formally called a single ended forward converter. Since I don't see any active reset circuitry for the transformer, I'll assume it'll be resonant reset. In which case you'll need a snubber from the MOSFET drains to the input cap, or ground. It is more efficient to connect the snubber to the input cap as you recapture that energy instead of shunting it to ground. This is what's probably killing your FET's. Next, there is NO WAY your going to drive 75 FET's with a 555!!!!! Contrary to popular belief, it's not the gate capacitance that you need to worry about (although, it is part of it) when switching MOSFET's, its total gate charge that is of interest.