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  1. duke37

    Computer Power Unit Failure

    You can find where the mains power comes in. It will or should have a filter consisting of some capacitors and inductors. If there are capacitors across the mains and one of them goes short circuit, then excessive current will flow. Check the mains input for ohms and disconnect any component to...
  2. duke37

    Oscilloscope does not display the correct waveform RIM Rog 7A

    The connectors are SO259 for PL259 plugs as commonly used for aerial connections to amateur transmitters. The resistors look to me to be normal carbon resistors except the green job which is likely to be wire wound in a ceramic mould and will withstand higher temperatures than the carbon...
  3. duke37

    Dimmer circuit help

    Try one diode first, that may be enough and will not drop the maximum voltage so much. I would put the diode in the positive wire to the motor, I like to keep the ground connection at ground all along the diagram. Just for neatness. You have a very good motor if it will run on only 1.25V.
  4. duke37

    frequency of oscillation in a twin t oscillator

    According to my book, the frequency of the twin T notch is F=1/(2*pi*R*C) Where is the square root?
  5. duke37

    frequency of oscillation in a twin t oscillator

    I might be able to do this if you add brackets such as 1/(SQRT(1/225) * 1e-9) You should have an even number of brackets.
  6. duke37

    Dimmer circuit help

    If I remember rightly, an LM317T controls with 1.25V btween the output and the control terminal so the minimum output in your circuit will be 1.25V, hence the motor not stopping. You can drop 0.6V with a silicon diode (1N400x etc.) so a couple of diodes in series with the motor will stop it.
  7. duke37

    dc switching power supply question

    What is the light? A bulb will have a very low resistance when it is cold. A bulb will run equally well on AC so could be fed with a simple transformer.
  8. duke37

    is there a such thing as a "variable relay"

    For 120V AC there will be a peak voltage of 120*SQRT(2) = 170V. There will also be spikes to take care of. I would suggest a 400V fet. A fet can not be used on AC.
  9. duke37

    555 Mosfet driver problems

    Could be incorrect ground problems because of the two power supplies. Put a led with a seies resistor directly across the source and gate to check the switching voltage.
  10. duke37

    For what value of L, will this circuit resonate at 332kHz?

    I agree Chris but he has not told us if he has b******d it. The original circuit uses large capacitors and very small inductors. The circuit Q is very high and losses in the inductors will be important. The bandwidth will be very small and a variable inductor will be necessary to tune the...
  11. duke37

    Inverter Circuit

    You do not need to change the circuit or the fets. You could use a fet with a lower on resistance or place two in parallel to reduce the power loss. The transformer should be large enough to have a low resistance. A fet can dissipate about 0.5W without a heat sink but in this case you wiil...
  12. duke37

    For what value of L, will this circuit resonate at 332kHz?

    I have a book (remember them?) by Arthur B. Williams, 'Electronic Filter Design Handbook' I have calculated the component values for a Butterworth bandpass response and plotted the results using 5Spice. You will need to make your own variable inductors and a signal generator to set the...
  13. duke37

    Inverter Circuit

    I have a scrap of paper where I have jotted down the on resistance of a IRF540 as 77mohm. Perhaps I am wrong! Taking 17A as the current, the voltage drop = 17 * .077 = 1.3V this is lost voltage. The power in the fet = 17 * 1.3 = 22W, this is lost power. You can divide this by 2 as said but...
  14. duke37

    diode for collapsing magnetic field

    An old trick is to put a bulb in the circuit to limit the fault current. Replace your diode with a new one which is in series with a bulb, you can then tell if the current is excessive.
  15. duke37

    For what value of L, will this circuit resonate at 332kHz?

    I have had another look at the circuit, I have made the lower coupling capactor 1F to effectively take it out of circuit. The Q is very, very high and in reality will have higher loss and wider response. You could trim it to get it nearer the correct frequency. What is wrong with the...
  16. duke37

    analoge to PWM with a fixed 10 MHZ frequency

    Show us your circuit inlcluding IC specifications. Can you run 100m in 8 seconds?
  17. duke37

    Inverter Circuit

    200W output will need 17A or so input, the IRF540 fets should be able to handle this but may need a heat sink. Chose a fet with low on resistance and sufficient voltage capability. The transformer will need to be of sufficient size to handle the current. If you are taking 20A then a 20AHr...
  18. duke37

    Charging 12v battery

    Do you have a dynamo or an alternator? Bicycle dynamos are in reality alternators and produce AC. A 6V AC source can be converted to 12V DC with a voltage doubler consisting of a capacitor and two diodes.
  19. duke37

    For what value of L, will this circuit resonate at 332kHz?

    As I said, I used 5spice for the simulation. You could replace the filter with one designed with the program that Chris shows but you will need terminating impedances to get it right. Where do the signals come from and where do they go? We may be able to guess the impedances. You will...
  20. duke37

    9v dc to 9v ac conversion

    I would think that an oscillator (4047?) driving an H-bridge would do the job but I have never used one.
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