Hello,
Is it possible to replace an adjustable regulator (like a LM317 ) with a fixed regulator?
The LM317 in circuit has +6v on the output, I'd like to drop in a +6v Dexa.
NewClassD UWB Regulator
I cannot think of any reason why this would not work, I just want to make sure I am not missing anything.
cheers
Kevin
Is it possible to replace an adjustable regulator (like a LM317 ) with a fixed regulator?
The LM317 in circuit has +6v on the output, I'd like to drop in a +6v Dexa.
NewClassD UWB Regulator
I cannot think of any reason why this would not work, I just want to make sure I am not missing anything.
cheers
Kevin
The LM317 is a really good performer if properly bypassed, better than its fixed cousins. No doubt one can do better with a discrete design, but that's a lot of money to replace a 317. It's debatable if it will have an actual measurable benefit, but after spending that much, I'd certainly be convinced that it did.
The NewClass D is only rated at 630mA where the LM317 is rated at 1A. Make sure you don't draw too much current.
it's the LM78xx that is rated at 1A. LM317 is rated at 1.5A.
but they will work with higher currents to if one have som "bigish" sinks and
close rail voltage. i run close to 2A out of a LM7812. with 15V in.
That wouldn't account for the center pin, which is Ground for the fixed types and Out for the LM317.you need to flip the fixed ones 180degree
What's the specification for an LM7812?i run close to 2A out of a LM7812. with 15V in.
Are you suggesting that others copy you and operate devices outside the manufacturers specification?
the heatsinks has little to do with the current passing through it.
but more the voltagedrop. if one run 25V in and 12V out. you will need some "big sinks" to pull any current. but with 15V in and 12V out, thats a whole other story.
lets say 1A current. at 25V in. thats 13W dissipation. at 15Vin its only 3W.
but more the voltagedrop. if one run 25V in and 12V out. you will need some "big sinks" to pull any current. but with 15V in and 12V out, thats a whole other story.
lets say 1A current. at 25V in. thats 13W dissipation. at 15Vin its only 3W.
I'll agree, but there is much to do with junction temperature (via the in-out differential, ie power dissipated in the reg, ie Tj), so heatsinking is quite relevant. There's current limiting and thermal shutdown to consider, so AndrewT is correct - it's treading into no-man's land.
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Well, guess what, I disagree with "pretty darn stable".
For 15Vdc @ 2Adc, I'd use 230:12Vac, 100VA transformer operating from 240Vac, feeding a bridge rectifier and 4u7F of smoothing.
Apply a -6% mains voltage variation. i.e. 225.6Vac for a check on whether regulator drop out occurs.
Input to regulator becomes a worst case low of about 14.8Vdc +-200mV of ripple. Giving a Vin from 14.6Vdc to 15Vdc.
Now apply a +6% mains voltage variation, i.e. 254.4Vac. to check for maximum Pd.
Input to regulator becomes a worst case high of about 16.72Vdc +-200mV of ripple.
For a 2A output the transformer is running at 50% o maximum continuous output and the regulator Pd varies from ~5.6W to ~9.4W
That is not "pretty darn stable".
The questioner should do something along the same lines as I have shown and insert his own data to arrive at his operational Pd and how much it can vary for his/her mains voltage variation.
For 15Vdc @ 2Adc, I'd use 230:12Vac, 100VA transformer operating from 240Vac, feeding a bridge rectifier and 4u7F of smoothing.
Apply a -6% mains voltage variation. i.e. 225.6Vac for a check on whether regulator drop out occurs.
Input to regulator becomes a worst case low of about 14.8Vdc +-200mV of ripple. Giving a Vin from 14.6Vdc to 15Vdc.
Now apply a +6% mains voltage variation, i.e. 254.4Vac. to check for maximum Pd.
Input to regulator becomes a worst case high of about 16.72Vdc +-200mV of ripple.
For a 2A output the transformer is running at 50% o maximum continuous output and the regulator Pd varies from ~5.6W to ~9.4W
That is not "pretty darn stable".
The questioner should do something along the same lines as I have shown and insert his own data to arrive at his operational Pd and how much it can vary for his/her mains voltage variation.
i don't know about you. but over here i have never had more then about 2-3% variation on mains.
Over here the line voltage can dip into the mid 90's and run as high as 128 during the summer == i had our electric company put a data logger on the main panel.
We had a competitor whose a.c. power was cut in the summer of 2007 -- their thermal curing ovens were powered by natural gas and didn't cut out quickly enough during the initial stage of a brownout -- what a mess!
If it's a low voltage application, I would try replacing the LM317 with one of the fixed voltage regulators in the LT1963A series -- there are 4 fixed voltage choices.
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