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发表于 2011-5-25 03:58:40
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you guys are talking about multiple issues:
1) ripple rejection: this is the regulator's ability to suppress input ripples from the output line. most regulators can do 60 - 80db (at 120hz). however, if your input is ripple free, you obviously wouldn't get any ripple on the output. so specifying output ripple voltages without specifying input ripple doesn't make any sense.
2) noise: even if the input is ripple free, a regulator will generate its noise on the output line. this is typically less than 0.01%, and usually around 0.001%. for a 5v regulator, that means the output noise is typically less than 500uv to 50uv. to get it down to 30uv isn't that unrealistic, with a good regulator. but getting it down to 5uv would be very difficult.
3) precision: 5% typical. so a 5v regulator is anywhere between 4.75 - 5.25. my experience is that they are usually in the 4.99 - 5.01 range.
4) thermal stability / drift: depending on your regulators but they will rarely exceed 0.1% on regulators using bandgap voltage source.
5) line regulation: all of the above assumes the load is a static load (aka a resistor). regulators are typically poor in terms of maintaining their output voltage into a dynamic load (a class B amplifier for example). under heavy load (over 100ma), you will find that your line regulation for a 5v regulator will be around 250mv - 500mv - for that reason, never ever use a regulator to power your class B amp. |
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