What does the efficiency bell curve of a good power supply look like?

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Discussion Overview

The discussion centers around the efficiency characteristics of power supplies, specifically focusing on the expected efficiency curve and its behavior across varying loads. Participants explore the implications of load dynamics, types of voltage regulators, and the conditions under which certain efficiency levels can be achieved.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question the existence of a bell curve for efficiency, suggesting that efficiency typically does not follow such a shape but rather experiences a rolloff at low and high currents.
  • There is a discussion about the factors affecting efficiency at low and high loads, including quiescent current in regulators and losses in switching transistors.
  • One participant raises the question of whether achieving 85% efficiency from a 10W to 1000W load in a switching power supply is realistic, prompting further inquiries about input voltage, output specifications, and load dynamics.
  • Another participant suggests that while achieving 85% efficiency across a wide load range is possible, it may require additional costs and design considerations, such as using different sub-regulators based on output loading.
  • Clarifications are made regarding the specific input and output parameters of the power supply in question, including the input voltage and output configuration.
  • Participants discuss the guaranteed minimum load of 10W and seek to define a reasonable load range for achieving the 85% efficiency target.
  • A link to external resources is provided for further reference on power supply efficiency standards.

Areas of Agreement / Disagreement

Participants express differing views on the shape of the efficiency curve and the feasibility of achieving 85% efficiency across a broad load range. There is no consensus on the specifics of the efficiency characteristics or the conditions necessary to achieve the stated efficiency goals.

Contextual Notes

Participants note various assumptions regarding input voltage, output specifications, and load stability, which may influence the discussion but remain unresolved.

david90
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What does the efficiency bell curve of a good power supply look like? Should the curve peak out at typical load?
 
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What bell curve? What kind of power supply voltage regulator?

I'll guess that you mean the rolloff in efficiency at very low and high currents? It wouldn't usually follow a bell curve, though, just droop some. At very low currents, the power burned by the quiescent current of the regulator itself (the current it consumes to run the regulator) becomes a more significant fraction of the input power compared to the output power. At high currents, the power drop across the switching transistors and across the winding resistances in switching regulators causes a drop in overall efficiency. A linear regulator will not lose efficiency as the output current gets up near the current limit, however.

Actually, it would take a more careful analysis with the linear at high currents. There might be a small loss of efficiency, based on the size of the current limit sensing resistor...
 
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Is it realistic to expect a 85% efficiency from 10W to 1000W load from a switching ps?
 
david90 said:
Is it realistic to expect a 85% efficiency from 10W to 1000W load from a switching ps?

That's a pretty big dynamic range. What are the input voltage and the impedance of the input voltage supply (like, is it the AC Mains, 110VAC, 20A breaker)? What is the output voltage and tolerance and allowed ripple? Are there limitations in terms of switching frequency? What are the cost limitations? How dynamic is the output loading? Like, does it swing from 10W to 1kW every second or so, or is it pretty steady once the load stabilizes? How quickly can it change?

My initial intuition is that yes, you can make 85% across that range, but it may take additional cost to be switching in different sub-regulator contributions, based on the output loading.
 
the input voltage will be 3phase 115rms phase to phase. There will be 4 48V outputs. The combined power of the outputs will be 1000W and there is no cost limitation. I guess the output loading is stable and does not swing.

Thanks for you help.
 
david90 said:
the input voltage will be 3phase 115rms phase to phase. There will be 4 48V outputs. The combined power of the outputs will be 1000W and there is no cost limitation. I guess the output loading is stable and does not swing.

Then yes, I would say that 85% is a reasonable efficiency goal. Where did the 10W number come from that you mentioned earlier?
 
10W is the guaranteed minimum load.

At what reasonable load range can the PS achieve 85%?
 
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