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  1. duke37

    Circuit with transistor: PLEASE HELP

    Ciao Welcome to the forum Please state what you know. The instructions are quite clear. The only thing left for you to consider is where to measure current (Ic). How would you do this? Have a go without the Ic measurement.
  2. duke37

    Electronic Project

    To get an answer, you will need to supply a circuit diagram. A transistor needs a low voltage drive at considerable current. A MOSFET will need a highish voltage at zero current. Considerable redesign may well be necessary.
  3. duke37

    i'm in very much confusion :\ teach me masters!!!!

    The motor is specified as 27 V DC V AC I do not understand what this is. Is the motor DC or AC or both. The speed is quoted as 3400 rpm. This does not match the frequency of the Indian supply (50Hz). Much more likely to be a motor made for the 60Hz USA supply. It could be a universal motor...
  4. duke37

    Help with antenna phantom power

    1. Not quite as simple. A choke has an internal capacitance between the turns so it will have a resonant frequency, It will act as a choke below this and a capacitor above this. If you have a grid dip oscillator, the resonant frequency of the 47μH choke can be measured. It is likely to be in the...
  5. duke37

    Power supply can't get zero volts

    Excellent result. One suggestion I would make is to connect the 2N3055 collector to the reservoir capacitor. This will reduce dissipation in the regulator and give a slightly higher maximum voltage.
  6. duke37

    Transistor Help

    The transistor needs about 0.6v between base and emitter. Subtract this from 2.5V and you will get close to what you measure. If you wish to use a common ground, you can use a p channel mosfet in the 5V line and drop its gate to turn it on. The resistance of the fet could be much less than 1Ω.
  7. duke37

    Is this schematic correct?

    The text says that the circuit resonates at about 55kHz with 147nF to tune it. If my abacus is correct, the inductance is 70μH. This is a very large discrepancy from my other estimate.
  8. duke37

    Is this schematic correct?

    There is a winding giving about 2μH. There is another winding, not much different so you will get twice the number of turns. The inductance is proportional to the square of the number of turns so 2μH * 2^2 = 8μH. Could be considerably less than this if there is a lot of leakage inductance when...
  9. duke37

    Is this schematic correct?

    Use the fewest turns (2 & 4) for the feedback. Connect the other two windings in series to give maximum inductance. (about 8μH?)
  10. duke37

    Is this schematic correct?

    Is the primary winding open circuit then?
  11. duke37

    Is this schematic correct?

    I would agree with the polarity suggestion. Note that there are three input coils which must be connected the right way round. If you have an inductance meter, the top two coils should be connected for maximum inductance. The base drive coil could be tried both way round.
  12. duke37

    Led Flashlight Help

    The AAA batteries have considerable resistance which limits the current. You can put a resistance in series with the power supply to get the same current as from the battery. You could drop the voltage of the psu but it will not be as stable as a resistance when temperature changes.
  13. duke37

    A zener diode question

    The resistance of a zener diode is used to describe the change in voltage as the current is changed. Often this resistance is taken as zero. Free? I was hoping for some Turkish delight.:D:D
  14. duke37

    radio waves

    The classic oscillator consists of a tank resonant circuit with power added to make it resonant and power taken out to feed the driver. The gain of this loop must be exactly one which needs to be set for low distortion. See AGC - automatic gain control. There are many variations of the...
  15. duke37

    Power supply can't get zero volts

    I do not have the tackle at present to load a diagram. All you need to do is to place a zener between the 741 output and the base of the 3055. So if the minimum output of the 741 is 2V and you place a 3.3V zener in the feed to the 3055 then it will not be turned on. The disadvantage is that the...
  16. duke37

    Two mic's, one CB

    In the UK you may have nothing else to do for a while other than work out a circuit youself if the driver uses it.
  17. duke37

    Led problems

    Where are you Gary?
  18. duke37

    triac based 50v to 110v battery charger

    You could measure the loco battery voltage and only connect the charger when it senses one of the three voltages. This would mean that no charging would occur if the battery was badly out of charge. There are car battery chargers which need some battery voltage with the right polarity before...
  19. duke37

    Shaded Pole Fan Motor - Speed Control Question

    The fan is driven by AC and so there will be an altermating flux in the stator. It is unclear whether the solid steel will increase the inductance and so reduce the current or give a shorted turn needing higher primary current and heat in the shunt. To get over this, use laminated steel from an...
  20. duke37

    Brig 001 amp: Left audio channel allways strangely quits working after some minutes

    The problem could be a temperature effect as previously stated. It could also be due to a leaky electrolytic capacitor which changes DC conditions. Measure voltages before and after the problem occurs.
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