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Old 10th October 2003, 12:00 PM   #1
Ralph is offline Ralph  Netherlands
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Default LM350 question

Working conditions are specified with Vin-Vout >= 3V. Does the regulator work better if I leave it let's say 4 or 5 Volt to work with?

My Vout is 5V @ 1.4A btw.
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Old 10th October 2003, 12:03 PM   #2
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Yes, under 3 V the regulator won't regulate. Calculate for worse case situations, low mains voltage and high load from the regulator. Don't forget about the ripple voltage also!
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Old 5th November 2003, 07:02 AM   #3
EE_Mark is offline EE_Mark  United States
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Default Dropout voltage

3 volts is the bare minimum they spec. They seem to work at slightly less than 3 volts but you're asking for trouble if you do that. 4 or 5 volts would be much better but remember the power dissipated in the regulator is the voltage across it times the current flowing through it. The LM350 is supposed to shut down if it goes too hot so at least it won't destroy itself. If you put in 10 volts and get out 5V@1.4 amps the regulator will dissipate 7 watts. Be sure and use a heatsink.
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Old 5th November 2003, 09:45 AM   #4
Ralph is offline Ralph  Netherlands
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I'm measuring 9,36 - 9,56 Vdc (depending on time of day) on Vin, so that looks good enough. (for 5V out)
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Old 7th November 2003, 06:03 PM   #5
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Ralph,
the input you measure is OK, but like Peranders said, don't forget the ripple voltage ( rimpel in nederlands ). This mainly depends on the size of your capacitor. If the ripple is 2Vtt you have to subtract 1V from the input you measured. In this case you are still ok, because you are above the 8V ( 5 +3 ).
For 1.4A out I would use 2200uF to be save.

Dick.
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Old 7th November 2003, 06:29 PM   #6
Ralph is offline Ralph  Netherlands
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Thanks Dick,

I measure very little AC on the input of the LM350 and use a large cap, so it must work out nicely. Thanks
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