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Power supply

  1. Oct 29, 2011 #1
    i want to make a 5v dc power supply for microcontroller i know how to make it i am going to use a 220v to 15v transformer and then by using capacitor and 7805 regulator ic i will convert it to 5v my question is as in transformer pout=pinput (ideally) by decresing the voltage from 220 to 15 the secondary current will increase can it damage the circuit(microcontroller[/SIZE])?
  2. jcsd
  3. Oct 29, 2011 #2


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    Did you just neglect to mention the rectifer you will need between the transformer and the regulator?
  4. Oct 29, 2011 #3
    Yes i forgot ofcouurse a bridge rectifier
  5. Oct 29, 2011 #4


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    The secondary current is defined by the secondary voltage and the secondary load resistance, not by the transformer turns ratio. The max secondary current that can be drawn is defined partially by the turns ratio.

    BTW, you also did not mention the safety circuitry that you have included in the design and construction of your power supply. Without very specific safety measures and circuits, your power supply presents a shock and fire hazard.

    Can you tell us what mandatory safety features you have included in your design?
  6. Oct 30, 2011 #5
    can you elaborate what partially means here and also what kind of safety equipment do you recommend?
  7. Oct 31, 2011 #6


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    Staff: Mentor

    For an ideal transformer, the turns ratio and the max input primary current would dictate the max secondary current that could be drawn. For a real transformer, however, there are resistance losses in the windings and core losses that lower the potential max output current from that ideal number.

    I'm not asking about safety "equipment", I'm asking about what design features are necessary in any equipment that connects to the AC mains, in order to help safeguard agains shock and fire hazards. What kinds of things would UL (in the United States) look for in your design if you submitted it for a safety approval? You need to include those things even in a hobby design, or you put yourself and other users of the power supply at risk....
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