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  1. I

    thermometer

    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...
  2. I

    difference b/w high frequency & transformer based inverters

    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!!
  3. I

    simple question about batt chargers

    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!!
  4. I

    Step up 1.5v to 9v converter

    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...
  5. I

    Switching Converters

    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...
  6. I

    Step up 1.5v to 9v converter

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

    Switching Converters

    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...
  8. I

    Switching Converters

    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...
  9. I

    0 ohm resistors

    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.
  10. I

    Simple transistor question (probably)

    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/
  11. I

    Very long RC time contant!

    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...
  12. I

    Inductance of a coil

    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?
  13. I

    Terminating a cable with a metallic braid

    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.
  14. I

    12V to 5V

    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...
  15. I

    help on bode plots...

    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...
  16. I

    Low-pass Filter?

    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...
  17. I

    Circuit Help

    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.
  18. I

    Circuit Help

    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.
  19. I

    Op amp theory Q's

    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"...
  20. I

    Op amp theory Q's

    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...
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