Power Supply Design - Input Protection Scheme
Re: Power Supply Design - Input Protection Scheme
If it's as high as 5.3 it's a reject. Spec says 4.9 to 5.1 IIRC. adjustable can be more finely trimmed.
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Re: Power Supply Design - Input Protection Scheme
ah yes, I am referring to the adjustable one in the RavAGE schematics (LM2931S I think it is) and not the fixed one (LM2937-5.0).
Re: Power Supply Design - Input Protection Scheme
What spec? What's an IIRC?Fred wrote:If it's as high as 5.3 it's a reject. Spec says 4.9 to 5.1 IIRC. adjustable can be more finely trimmed.
The reference voltage for the LM2941 has a +/- 5% tolerance over temperature (see data sheet), so you are starting off with that.Dan wrote:regulator output voltage is approx 5.02V when using correctly spec'd resistors (attention paid to tolerance)should never ever get to 5.30V.
Thanks,
Huff
Re: Power Supply Design - Input Protection Scheme
Table from datasheet below!TonyS wrote:The reference voltage for the LM2941 has a +/- 5% tolerance over temperature (see data sheet), so you are starting off with that.
Thanks,
Huff
Where does this +/- 5% you speak of exist?
Re: Power Supply Design - Input Protection Scheme
Look at the first Parameter ("Reference Voltage") on page 3 (sorry, but I do not know how to copy / paste from the data sheet).
So even if you use 0.01% resistors to obtain 1.275V at 5.00V, the regulator may try to regulate the output to obtain 1.211 to 1.339V at it's adjust pin.
Note that the "Output Voltage" graph is "Typical" and assumes that you were at 5.00V @ ~ 20C to begin with.
Thanks,
Huff
So even if you use 0.01% resistors to obtain 1.275V at 5.00V, the regulator may try to regulate the output to obtain 1.211 to 1.339V at it's adjust pin.
Note that the "Output Voltage" graph is "Typical" and assumes that you were at 5.00V @ ~ 20C to begin with.
Thanks,
Huff
Re: Power Supply Design - Input Protection Scheme
https://duckduckgo.com/?q=(1.313+%2F+1.275)+*+5 == 5.14901960784314 absolute worst case at 25C
https://duckduckgo.com/?q=%281.339+%2F+1.275%29+*+5 == 5.25098039215686 for full temperature range extreme
Typical values are MUCH better than specced, though. This can/could/should/will be part of test procedure. If your reg is pumping out too much, trim it down a bit before installing the clamp. And/or acceptable steady state current draw fully assembled post production before shipping.
https://duckduckgo.com/?q=%281.339+%2F+1.275%29+*+5 == 5.25098039215686 for full temperature range extreme
Typical values are MUCH better than specced, though. This can/could/should/will be part of test procedure. If your reg is pumping out too much, trim it down a bit before installing the clamp. And/or acceptable steady state current draw fully assembled post production before shipping.
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Re: Power Supply Design - Input Protection Scheme
HUH?
So "Quality" and "DIY" and "NOOB" go out the window cause we don't like reality? A 5% part was picked, if that is not acceptable, pick another part or review the topology.
So "Quality" and "DIY" and "NOOB" go out the window cause we don't like reality? A 5% part was picked, if that is not acceptable, pick another part or review the topology.
Re: Power Supply Design - Input Protection Scheme
Ahh, what? I don't even understand what it is that you're *trying* to say. How many of these parts have you handled and measured? I've never seen one over 5.1V, and I've measured plenty. Nor under 4.9, for that matter. Those values (both hot and cold) represent the absolute corners of a bell curve, whereby the vast majority of parts come no where near those values. As with any design decision, you play into statistics with it. If you're happy for 5% to require rework to work properly, then you can pick a voltage based on that and a known statistical distribution.
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