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  • Electronics Questions

    I am building the sproggy type PSU and I have a few general electronics questions

    a) is using a 1800uF 25V cap ok? (a 35V is specified)

    b) is there any equivalents to the T6(q4339) flyback tranformer?

    Q4339 specs

    c)is a 470R 1/2W resistor the same as a 470K 1/2W resistor?

    Thanks
    [SIZE=1]'91 Nissan Stanza

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  • #2
    Machs_FueL,
    You should not go lower in voltage rating for capacitors, so use a 35V cap if that is what is called for. I don't know about the flyback transformer, but I think a 470R resistor is 470 ohms, while a 470K is definitely 470,000 ohms, so they are not the same.
    Good Luck
    Mike

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    • #3
      Originally posted by Machs_FueL:
      <STRONG>
      a) is using a 1800uF 25V cap ok? (a 35V is specified)

      b) is there any equivalents to the T6(q4339) flyback tranformer?

      Q4339 specs

      c)is a 470R 1/2W resistor the same as a 470K 1/2W resistor?

      Thanks </STRONG>

      Actually you would be just fine using a 25 volt cap. Usually the rule is you de-rate by 50% percent so for the case when you need 12 volts (from sproggy's schematic) the minimum you would want to go is 18 volts. So a cap rated for 25 volts would be just fine.

      I'm not so sure for the transformer question. You want to know the current capabilities of the coils. The level at which the core saturates and the winding info. If you can match these three quantities for another coil you should be just fine. IE, look for the same core material, same gauge wire, same number of turns...


      For the resistor you want to use a 470 OHM resistor. a 470k resistor would not light that LED very much. Think of an LED as having a 2.4 volt drop and a current draw of 20mA. If you hook 5 volts up you want a resistor to drop the other 2.6 volts to add up to 5. so 2.6/470 = 5 mA. This LED is already going to be kinda dim. You could even use a 220 Ohm resistor for that. That would give you about 11 mA. Note, all these calculations are approximate. Super high brightness LEDs like around 80 mA. Really tiny LEDs can do just fine with 5 mA. Newer technologies are also a lot brighter with less current. etc etc etc..

      Jeff_
      MPEGBOX - Plexiglass Computer
      www.mpegbox.com

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