Search results

  1. L

    need help with RLC circuit

    It may help one's understanding to see what is going on with the help of a phasor diagram. But first note that capacitive reactance, X{C}, and inductive reactance, X{L} are given in the problem statement; however, impedance is required to perform the circuit calculations. Impedance can be...
  2. L

    need help with RLC circuit

    No. It is not possible to do this problem with just magnitudes, the phase angles must also be accounted for. You need to use complex algebra or a phasor diagram.
  3. L

    need help with RLC circuit

    The only solution is to calculate the complex impedance of the circuit and use that to find the current, I=V/Z. Or else find the magnitude & phase of each component current, then use the general method for adding vectors to get the total current.
  4. L

    need help with RLC circuit

    The formula used in #2 is a shortcut used when the phase angle between vectors is 90°. Why do you think that would apply here?
  5. L

    Homemade Capacitor

    One more flogging......Consider that whatever you can create in your kitchen will not have the volumetric efficiency of a commercial polyester film capacitor. So choose an appropriate film capacitor, determine how many would be necessary to satisfy your farad capacity needs, then arrange them...
  6. L

    sample and hold pulse source?

    Have you looked at using mono-stables in tandem? One generates the long delay and triggers the other to generate the short pulse.
  7. L

    B&K Precision better than Tektronix ? (Oscilloscopes)

    B&K is not just another cheap brand, but they do have some cheap options. More important than the technical specifications is the warranty. You are comparing a B&K having a 1-year warranty (other B&K scopes have a much longer warranty) to a Tek with a 5-year warranty. I like the better B&K...
  8. L

    LPF and HPF

    It is annoying whenever a serial pedant hijacks a thread to focus instead on terminology that is normally used in discussing circuit theory, and mercilessly explains why it would be wrong when taken literally in the realm of device physics. Webster's New Collegiate Dictionary pedant - one who...
  9. L

    LPF and HPF

    I understand what you did, and that is why I know you failed. When asked to analyze the network model of a capacitor, you immediately jump to the physical approximation of the capacitor network model and analyze that instead. The reason you fail is that you wear blinders that keep you from...
  10. L

    LPF and HPF

    You have changed the question from one of current flowing through a network model to the issue of charge movement in the physical approximation of the network model. Since you did not answer the original question, you get zero points for that response.
  11. L

    LPF and HPF

    Then please show from the defining differential equation Ic=Cd/dtVc that current does not flow through the capacitor network model.
  12. L

    LPF and HPF

    I keep trying to explain how to interpret that statement, but you keep insisting your misinterpretation is paramount. This is a clue about linear circuit theory for those who may aspire to advanced study of network analysis and synthesis. Device physics are not relevant to circuit analysis...
  13. L

    LPF and HPF

    Since you insist on misinterpretation, I'd say that is your problem - not mine.
  14. L

    LPF and HPF

    That is just plain false. Oliver Heaviside demonstrated how to treat the current flowing through a capacitor exactly the same as current flowing through a resistor. This concept is fundamental to linear circuit theory. Note that I posted some of Heaviside's work on that topic a while back...
  15. L

    LPF and HPF

    If you Laplace transform a capacitor, whaddya get? Actually though, linear circuit analysis is not concerned with the physics of electrical components. What we call a 'capacitor' is just a model of a one-port network where current flowing through the network behaves according to the...
  16. L

    LPF and HPF

    That kind of thinking is so mired in the time domain. Linear circuit theory is based in the complex-frequency domain where capacitive current obeys Ohm's Law. However, the circuits in the complex-frequency domain are the Laplace transform of their counterpart in the time domain. While time...
  17. L

    How to get 80 mV?

    Experienced designers might ask you what impedance level you need. But if all you give them is a blank stare, then they might ask how much current will be drawn from this voltage reference of 80 mV and how far can the voltage deviate over the current range. If you still have a quizzical look...
  18. L

    Trying to replace resistor on a remote keyless gate access panel.

    Looks like that resistor burned out real good. It is possible that fire ants congregating around the resistor impeded the convection cooling by blocking air circulation. Yes you can replace the burned resistor by cutting it out then melting the solder and removing the old wires. But R16 does...
  19. L

    LPF and HPF

    Another way to write τ>>t would be t<<τ or t=0+ for initial start-up or turn-on of the circuit. But a capacitor doesn't know if it is in a LPF or HPF, it just behaves according to the defining equation Ic=Cd/dtVc. So at t=0+ the voltage across the capacitor is zero (and rising) but the current...
  20. L

    ECG circuit digram with AD620 and 741 op amp as a gain differentiator

    Can I assume that you just want to lower the impedance level of the ECG Signal? In that case use a 741 as a voltage follower (gain = +1) and connect the ECG Signal to the +input of the 741. The output of the 741 will be a replica of the ECG Signal at a lower impedance level.
Top