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audioguru last won the day on August 10

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  1. Using a single color red LED: A CD4017 powered from 9V can output 16mA into a 2V red LED on each output which is enough to burn out its output transistors. Use 150 ohm series current-limiting resistors to share the heat.
  2. audioguru

    FM Transmitter

    The frequency of FM broadcasting is high enough so that the signals go straight and far if there is nothing blocking them. But the curvature of the earth blocks distant reception. Of course the range depends on the transmitting power and direction, and the sensitivity and direction of the receiver. My FM transmitter circuit produces about 0.28W into a 75 ohms 80cm whip antenna. Its range is 2km across a large river valley to a very sensitive home stereo tuner or car radio, down the street to a cheap Sony Walkman radio, and across the street to a cheap clock radio. The tx and rx antennas must be parallel to get these ranges. There is an FM radio station about 50km away from me with its antenna mounted on a small mountain. They get complaints of poor reception due to hills that block their signal.
  3. audioguru

    0-30 Vdc Stabilized Power Supply

    How can you use an LM339 without reading its datasheet? Since its output is "open collector" then it cannot turn on the transistor unless you add a "pullup resistor". The output of your 10A rectifier does not connect to "regulator in". Instead it has a huge filter capacitor (12000uF) and it powers the driver and output transistors of the regulator circuit. R13 should connect to the fixed +40V. When you switch taps then the huge filter capacitor must instantly charge with an enormous current that will burn out or weld the relay contacts.
  4. audioguru

    0-30 Vdc Stabilized Power Supply

    Each comparator in an LM339 has an output current of only 4mA. Relay coils need more current so transistors or Fets must be in between. Your block diagram is missing the huge filter capacitor needed that might burn out the relay contacts when the relays switch taps.
  5. audioguru

    Help with a simple lm317 circuit

    You should always read the datasheet for an electronic part to see what is needed and why. The datasheet for an LM317 shows an input to ground disc capacitor of 0.1uF and an output to ground electrolytic capacitor of 25uF or more. The datasheet shows the more expensive LM117 that can use a resistor as high as 240 ohms from ADJ to OUT pins, a cheaper LM317 needs 120 ohms max. Then your 360 resistor should be 180 ohms. Solderless breadboards cause many connection problems. Solder all the connections together on a pcb or stripboard to eliminate the connection problems.
  6. audioguru

    0-30 Vdc Stabilized Power Supply

    Simply test voltages in the circuit with a voltmeter. The opamp U2 controls output voltage regulation and it has an extremely high internal voltage gain (220 thousand times for a TLE2141). The negative feedback of the circuit detects any output voltage loss and directs U2 to correct it. I think your poor voltage regulation is caused by the wiring from the output of the circuit to your load is too thin and causes the voltage loss.
  7. audioguru

    Help with a simple lm317 circuit

    You forgot to attach your schematic so we can see the resistor values and important input and output capacitor values. Maybe the wallwart has very poor or no filtering then its "12V" is fluttering, averaging a voltage much less than the minimum of 5V that the LM317 needs. Maybe the wallwart is overloaded since you did not say how many LEDs or how much current they need. The original AA cells are pretty big and can produce a lot of current.
  8. audioguru

    0-30 Vdc Stabilized Power Supply

    The original defective circuit had many overloaded parts that will blow up. The improved version fixes it. Opamp U3 senses the output current in R7 and reduces the output voltage and output current to match the current set with P2. The maximum output current is 3.0A in the improved circuit and the two output transistors have a total maximum current rating of 30A so they will not blow up with only 3.0A.
  9. No. An old condenser mic uses 48V and needs a preamp with a very high input impedance. It does nothing in your circuit. A modern electret mic (look it up in Google) is a condenser mic with 48V stored permanently in its electret material and has a Jfet inside that has a very high input impedance. The datasheets of electret mics show that the Jfet current is about 0.5mA and needs 2V to 10V, so your circuit will not work since the current in the 47K resistor reduces the voltage and current much too low. For 2.5V across a 0.5mA electret mic and a 5V supply then the resistor must be only (5V - 2.5V)/0.5mA= 5k but the 5k resistor and any other load (your volume control) loads down the output level. I use a 10k resistor and an 8V supply. Then it feeds a preamp with a 100K input impedance.
  10. The datasheet of a CD4017B shows that its output current into a 2V LED when it has a 5V supply is only 3.5mA or less (looks dim). Your circuit is mixing an old TTL 555 with an output voltage fairly low with a Cmos 4017 that needs a fairly high clock input voltage. A bad mix. I used a 74HC4017 (high current Cmos) clocked with a Cmos 555 and it makes very bright LEDs and since they are both Cmos they work together reliably.
  11. audioguru

    0-30V Stabilized Power Supply

    Why do you show an LT1038? it is obsolete and is not made anymore. It is impossible for it to dissipate 32V x 10A= 320W. Its datasheet shows that with a huge heatsink with fan or with liquid nitrogen for cooling it can dissipate only 120W. Its control circuit gives 10A only when its input to output is a few volts and cuts the max current to 2.5A when the input to output is 30V.
  12. Why do you show text that talks about an NPN transistor but you show a schematic with a PNP transistor? The Circuitspedia PNP circuit is missing the important diode parallel with the relay coil. The diode is shown on their NPN circuit.
  13. audioguru

    0-30 Vdc Stabilized Power Supply

    Surface mount ICs on adapters? Solder that was dripped on from up high and heated with a blow torch? All I can say after seeing your project is "EEK!".
  14. audioguru

    0-30 Vdc Stabilized Power Supply

    No and No. U1 has a gain of 2 times and a 5.6V Zener diode. Therefore its output is 11.2V, not 33V. A 5.6V Zener diode does not change its voltage when its temperature changes but an 11.2V Zener diode increases its voltage if it gets warmer. The BD139 and the output transistors are emitter-followers. Their emitter voltage follows their base voltage but at high current, their base voltage is 1V to 1.5V higher than their emitter voltage. Then when the output voltage is 30V the output of U2 must be 32V to 32.5V.