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  1. audioguru2

    "Power?" Inverter

    This project has its capacitors backwards! Tantalum and Electrolytic capacitors blow up if the polarity is backwards and the current is high. The 180 ohm base resistors supply hardly any base current and the power transistors have low current gain, so the output power is very low, less than...
  2. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    The current in the light bulb when it is very bright is only 25W/240V= 0.1A. Since yours is dim then its operating power and current are a lot less. Maybe you can fix the cause of the hot transistor: 1) Swap the Tesla output transistors. 2) Swap the BD234 driver transistors. 3) Swap the 15 ohm...
  3. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    It looks like my 4W and 7W night-light bulbs, except it is dimmed.
  4. audioguru2

    "Power?" Inverter

    Many other members tried to get this project to work by using electrolytic capacitors instead of tantalum. They even tried it with the capacitors connected with the correct polarity. Onix says his project is "successful". He didn't say how many Watts, volts or amps is its output. The text in...
  5. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Steven, You wrote that the microwave lightbulb is marked 2A at 250V. That is 500W! The lightbulb would cook the food and the microwaves aren't needed. Look again, it is probably marked, "0.2A". Then it would be 50W at 250V or 40W at your 240V.
  6. audioguru2

    a high pass filter question

    It is easy to get some voltage gain from a transistor circuit and even easier to get lots of voltage gain from an opamp. A common emitter transistor stage has a voltage gain of RC/(Re + RE). If the emitter is bypassed to ground with a capacitor to remove RE from the calculation and the circuit...
  7. audioguru2

    CICUIT WORKING

    The diodes are used to increase the input turn on voltage of the ULN2003. They aren't needed. i 1) Look at the datasheet for the diodes to see that their small differences won't make any difference in this circuit. The diodes and 1k resistors are not needed at the input of a ULN2003A. 2) The...
  8. audioguru2

    BJT biasing

    Hi Kevin, Transistors last "forever" if you operate them within their ratings for voltage (including the max of only 5V to 7V for reversed biased emitter-base junction), max current and  min and max temperature (ambient and power dissipation). All transistors have less current gain (beta) at...
  9. audioguru2

    a high pass filter question

    No Kevin. Many circuits have an input that is not affected by the output: 1) An audio amplifier input isn't affected if the output has an 8 ohm speaker connected or nothing connected. 2) An opamp input isn't affected if its output is loaded or even shorted. 3) A common emitter single transistor...
  10. audioguru2

    220 volts Versus 120 volts

    Hi Kevin, I have 120VAC mains in Canada for most electrical receptacles, but my stove, clothes dryer and air conditioning operate from the 240V that is in my home. It is one 120VAC phase and neutral and an opposite 120VAC phase and neutral. The neutral is connected to ground.
  11. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    No. The huge TIP142 is completely different. It is an NPN darlington transistor. A TIP32 is a PNP single transistor, is not too big and will replace the BD234. No. The 2N3058 is a small PNP transistor, not an NPN power transistor like the 2N3055. You need a power transistor with high current...
  12. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Steven, Why do you want to replace the BD234 transistors in your inverter circuit?
  13. audioguru2

    need two coloured wire

    Thin, thick, solid or stranded wire. You don't say. Wire has a gauge number that says its size. Stranded wire is more flexible than solid wire. These spec's are much more important than the colour of its insulation.
  14. audioguru2

    4ch rc schematic help

    No. The resistor controls the infrared frequency. You would have a difficult time controlling something that moves with infrared. Your TV remote uses infrared. The radio is a completely separate circuit and the receiver is so cheap that only a few would be able to run around together. Model...
  15. audioguru2

    4ch rc schematic help

    Go to Taiwan and buy a few thousand of those cheap toy transmitters and receivers. The datasheet shows them in a toy car and they control bang to the left, bang to the right or straight. You steer by banging. It also has  reverse and  turbo "quickly kill the battery" functions. They have a...
  16. audioguru2

    Question on the Plants Watering Watcher circuit

    IC1c was the blinking oscillator. It isn't used so I disabled it by connecting both inputs high. Connect nothing to its output.
  17. audioguru2

    BJT biasing formulas

  18. audioguru2

    Telephone Ring Circuit

    Use a double-throw switch to disconnect your phone and connect the 60VAC to the line to make the other phone ring. But you won't have a circuit to stop the ringing when the other phone answers so the 60VAC might make a very loud noise in the other phone's handset then destroy the electronics in...
  19. audioguru2

    BJT biasing formulas

    Correct. No. The mic impedance is about 5k and it is in parallel with its 10k load/powering resistor so it has an effective series resistance of 3.3k. The 3.3k, the 330nF coupling capacitor and the 11.2k load resistance are all in series so the cutoff frequency is 1/(2 pi C1 [3.3k + 11.2K])=...
  20. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi steven, Hundreds of transistors will replace the BD234 in that circuit. The TIP32 for example costs $.60US. Why replace the BD234 driver/oscillator transistors? It is the 2N3055 transistors at the outputs that do all the work and if they are paralleled then the output power might be a little...
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