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Everything posted by indulis

  1. John I know the math...... for a second order, the transfer function solution is quadratic, but you're the "theory expert", so can you explain, in technical terms why the gain doesn't start to roll off a decade before the corner frequency?
  2. That doesn't show me the math or answer the question.
  3. Show me the math................. A Butterworth filter, irregardless of order, only has poles in it's transfer function, so could you explain.... "A Butterworth two-pole active filter uses a form of positive feedback to hold the output up just before the cutoff frequency."
  4. Varying the duty cycle will change the speed, and a fixed duty cycle will cause the speed to remain constant, but that will ONLY work if you have a constant load on the motor. If the load can change, then you'll need feedback (like a tachometer) if you want to maintain the constant speed. Why not just use 2 of the half bridge drivers. Then you don't have to worry about how the MOSFET's get turned off.
  5. Not really. If the battery you were charging was trying to draw more than 15A, the charger would just bounce on and off. You don't want to limit the current to 15A, but regulate it to no more than 15A. Take a look at some of the apps notes from National on 5A adjustable regulators. You should find a schematic for a battery charger. Use 3 of the regulators and re-calculate the values for 24V operation.
  6. "Optimum" battery charging is far more complicated!!!! Each different chemistry will have it's own optimum charging profile with different charge rates to specific voltage levels, dwell times and float charge levels. Optimum charging is NEVER linear and can have multiple voltage level dwell times.
  7. Looks like a PWM (around 59KHz??) motor speed controller, and you're trying to multiplex the half bridge driver? How big is the motor , and what's it going to do... ???
  8. I would disagree, at the die level there is 100% static and some dynamic testing done because it cost too much to finish processing the wafer using a bad "chip". Way back, when I worked as a design engineer at LTX (www.ltx.com), a manufacturer of mainframe semiconductor test equipment, part of what I did was design prober/handler interfaces. The manufacturers want/need a way to decide if a part gets sold to the government or to Radio Shack, and the ONLY way to tell is by testing.
  9. Sure, your MTBF would be affected running any component at it's limit. What determines a resistors wattage... like everything else, a certain temperature rise!!! As long as you can keep it "cool" your OK. Convection, while better than radiation, still isn't as good as conduction, for thermal cooling, so why would you want to move the resistor further away from the PCB. If it's a power run, it should have nice BIG & FAT copper traces which should have much more surface area than the resistor itself. I can't be 100% certain about thru-hole components (been away from them too long), but SMT resistors have to be de-rated over temperature. While it would be nice to have 50% de-ratings, there can be times when things like that can actually hurt you... take a SMPS primary switching FET for example. Say you look at the drain waveform and see a 120V spike. Now, a 150V MOSFET might have a Rds on of say... 50 milliohms and work just fine, while a 250V MOSFET might have a Rds on of 150 milliohms, so that's a factor of 3 higher for power dissipated... which one would you use??? Of course it would be the 150V MOSFET!!!!
  10. I've never seen an op-amp with an emitter follower configuration as an output stage, just a totem pole. Anyone have a part number for a op-amp with a emitter follower output stage??
  11. What are you trying to measure?? If you have an ammeter, why do need a shunt?
  12. The notice say's ... the diode is needed when the INPUT is shorted, not the output. While in die form, you can bet that each and every one is tested for sure!!!!!!!!
  13. Do a google search on "mag amps"................
  14. Just a few general comments about the switching power supply…. The 100KHz 3842 design looks to be current mode forward converter. As such, by definition it doesn’t have current limit. It has power limiting… the output current will continue to increase as the output voltage collapses, thus holding the power constant. Also, the LM339 shown in the secondary will not work!!! You can’t use an open collector comparator as an op-amp!! C7 should be in parallel with C8. You might need snubbers on the secondary rectifier and flywheel diodes. For the min output inductor value don’t forget about 1/2*L* I^2*F. It will be VERY hard to compensate this feedback loop!!!!!! The larger you make the output capacitor, the more it will pull back the crossover frequency (very bad transient response). I don’t see any slope compensation anywhere. You will find that it is VERY hard to make most switching power supplies run with zero load and not loose regulation!!!! What’s the core material for the EER42? What’s you max/min duty cycle?
  15. Yeah, I'm sure C8 is used as a loop compensation cap (limit/control U3 output slew, but that's what feedback is all about), but that doesn't stop it from being a integrator, which IT IS!!!! I saw a post on another fourm that covered feedback in comparators circuits and why it is used!!!
  16. What you are talking about are called "latching relays". They have two coils, energize one and it flips one way, energize the other coil and it flips the other way. Also since they a latching, you don't have to have power applied to the coil all the time. I have only seen these as small, mercury wetted, single and dual "form C" (form C = SPDT) low current relays.... if I recall Magnecraft makes some.
  17. U3 is "not really" used as a comparator, at least not in a "true sense". It is true, while the output current draw is below the current set point level, the output of U3 is sitting at the positive rail, but that's where the comparator similarity ends. It's configured as an integrator.......... as the voltage across R7 increases, and for the sake of simplicity, I'll say U3 starts to "turn-on" (go towards it's negative rail), the clamp diode D9 starts to pull down the output voltage set point votage at U2 pin 3. It will only pull it down as far as it needs to so that the current limit point is not exceeded (foldback). C8 controls the rate at which the level changes. U3 does not slam to the negative rail like a comparator would, although it could go there if it needed too. In fact, if U3 was being uesd as a true comparator, the power supply would go into a "hic-up mode" as U3 went rail-to-rail.
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