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What should I consider while designing a power supply for a device ?

I need to design a power supply for an RF module, that need 3.3 V DC

All I know till now that I should take care about :The voltage in needs , the current & output impedance of my power supply ?

any more hints ? any general notes about designing power supplies ?

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Ask a specific question. This is way too broad for here. – Olin Lathrop Mar 24 '12 at 20:33
@OlinLathrop Can it be as a general consideration when designing a DC power supply ? To make a professional electronic design ? – xsari3x Mar 24 '12 at 22:07

closed as not a real question by Olin Lathrop, Madmanguruman, W5VO♦ Aug 28 '12 at 0:51

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

2 Answers

up vote 2 down vote accepted

I'll answer this in terms of what specifications should you nail down before you get started with the design. I'm sure I'll forget something, and there will always be a special situation that introduces new requirements, but to get started:

  • What is the output voltage and current requirement?
  • What is the input voltage; is it ac or dc; is it stable or varying?
  • What is the required isolation between input and output?
  • What is the maximum cost for the supply?
  • What is the maximum size (volume or board area)?
  • What is the available cooling (forced air or convection)?
  • What is the required ambient operating temperature range?
  • Do you need a slow-start feature?
  • Do you need over-current protection?
  • Do you need over-temperature protection?
  • Do you need any kind of external enable/disable/reset control?

For ac-input supplies:

  • What are the local safety regulations?
  • How variable is the local mains voltage?
  • What is the required fuse?
  • What are the required separations for wires connected to mains from other wires?
  • Do you need inrush current limiting?
  • Do you need power factor correction?
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up vote 1 down vote

You need to consider: input voltage range, power, efficiency, size, weight, cost, line regulation, load regulation, noise and ripple limits, type of current limit, operating and storage temperature, design life, altitute, EMC - conducted, radiated noise, harmonics, dips, flicker, immunity and emissions, safety approval - creepage and clearance, component materials for flammablility, isolation voltage, fusing, case design, ventillation, audible hum, switching cycle life, inrush, overvoltage protection, surges and transients, leakage currents, common and differential mode noise, and probably many more. That's why, unless you are designing for high volume, its best just to buy them.

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