Recent content by Paul_J

  1. Paul_J

    Audio amp quiscent current

    The circuit is different from Sanyo's. The trimpot is an ordinary one, nothing special. I could easily find a replacement if I had to. The output stage seems to be a triple Darlington - all TOSHIBA. I'll find a way to fix this. Thanks anyway.
  2. Paul_J

    Digitally controller PSU

    You can use a step-down converter for the 5V part. It's more efficient so it doesn't require a large heatsink. At 3A the IC will need an external transistor. The value of the inductor can be calculated with the formulas in the Application Note. MC34063_ST.pdf TL494_AppNote_-_slva001d.pdf
  3. Paul_J

    Audio amp quiscent current

    Because it's a rare amp I don't have a schematic. It's hard to guess it by looking at the PCB tracks because there's also a circuit that detects if there's DC at the output. I think the value of the trimpot is too large. The trimpot connects to a transistor. If this doesn't work I'll use a...
  4. Paul_J

    Audio amp quiscent current

    I replaced a STK3062 in a Marantz PM-52SE power amp with another module. The output DC offset voltage is 0 but the quiscent current in 700mA.  :o What should I do to reduce it to 70mA? Here's a list with the values of the components of the replacement module: R1______________47K  1/4W...
  5. Paul_J

    Heatsink Surface Area

    So, would 30cm2 of heatsink surface be enough for each watt of dissipated power? Even if the heatsink calculated with the above formula is a little bit oversized it doesn't matter. In fact, the cooler a semiconductor runs the longer it lasts. I could build a unit for testing heatsinks because I...
  6. Paul_J

    Power dissipation limiter

    Here's the circuit. I know it will work but I'm developing a better version which I'm not sure how well it works...
  7. Paul_J

    Heatsink Surface Area

    Radiation matters more if the heatsink is painted in matte black, but it's a lot less than the heat transferred to the ambient by convection. I could measure the thermal resistance if I have a contact thermometer... and apply a known voltage to a known value resistor stuck to the heatsink. I...
  8. Paul_J

    Use of LM324 in audio circuit

    I used the LM358, which is the same thing except that it has two opamps instead of four and it works well. I built a preamp and a stereo width controller (which is actually a channel mixer) using this IC. If you want lower noise then use the TL074. The power supply must be regulated and within...
  9. Paul_J

    Power dissipation limiter

    :o No. If the voltage across the transistor increases, the SCR, which is placed between the bridge rectifier and the filter capacitor, will stop conducting until the voltage decreases under a value set by a Zener diode. The variable voltage linear power supply will be connected after the SCR...
  10. Paul_J

    Power dissipation limiter

    The LM723 does have a circuit with foldback current limiting... How about using the other way to limit the dissipated power - the one with the SCR (thyristor)?
  11. Paul_J

    Heatsink Surface Area

    How can I determine the approximate thermal resistance of a heatsink if I know its surface area?  ::) I searched the web and the most useful thing I found was this http://www.jaycar.com.au/images_uploaded/heatsink.pdf but it doesn't answer my question.
  12. Paul_J

    Power dissipation limiter

    Hi guys, Foldback current limiting would be a solution... I know this method of current limiting from a book about voltage regulators. It has all the formulas for calculating the output short citcuit current... How can I adapt it to this circuit...
  13. Paul_J

    Power dissipation limiter

    Wishing to build a variable DC power supply with current limiting I came across this problem: when the output is short circuited to ground and with the current limit set to maximum the series pass element (in this case a transistor) has to dissipate all the power so it requires a big heatsink...
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