Need a 40V input rated version of the lm7815 regulator.
Need a 40V input rated version of the lm7815 regulator.
(OP)
Hello all,
I am working on a power supply board which has produces 15V, and 24V outputs. The transformer we're using outputs roughly 36-37VDC unfiltered which gets sent into a lm7815 regulator to make the 15V output, we can't use a transformer with lower output because we need the higher voltage to feed the buck regulator which outputs 24V. We're exceeding the 35V limit for the lm7815 regulator (it hasn't died yet) and it would be nice if I could find a fixed 15V output 3 terminal regulator, either in the to-220 packadge or something with three terminals spaced 100 mils apart. I need one that is rated for 40VDC or higher.
So far all I could find is the Fairchild KA78T15 regulator, which WOULD be perfect, however from what I've been able to tell its an obsolete part and only Rochester Electronics is selling those parts and this board is expected to last 10 years, so we don't want to be limited to one supplier.
Does anyone know of a 15V fixed output 3 terminal regulator that can handle up to 40V or more input voltage, preferably in the to-220 package? Current requirements aren't too high, 500mA would probably suffice.
I have seen a high voltage version of the LM317 that can do up to 60Vin, I may try to use that if I have to, but we're trying not to have to modify this board any more to fit the extra components required for an adjustable regulator.
Does anyone have any ideas? We may be able to use a 3 pin buck regulator chip, provided it has a reasonably clean output.
-Robby
I am working on a power supply board which has produces 15V, and 24V outputs. The transformer we're using outputs roughly 36-37VDC unfiltered which gets sent into a lm7815 regulator to make the 15V output, we can't use a transformer with lower output because we need the higher voltage to feed the buck regulator which outputs 24V. We're exceeding the 35V limit for the lm7815 regulator (it hasn't died yet) and it would be nice if I could find a fixed 15V output 3 terminal regulator, either in the to-220 packadge or something with three terminals spaced 100 mils apart. I need one that is rated for 40VDC or higher.
So far all I could find is the Fairchild KA78T15 regulator, which WOULD be perfect, however from what I've been able to tell its an obsolete part and only Rochester Electronics is selling those parts and this board is expected to last 10 years, so we don't want to be limited to one supplier.
Does anyone know of a 15V fixed output 3 terminal regulator that can handle up to 40V or more input voltage, preferably in the to-220 package? Current requirements aren't too high, 500mA would probably suffice.
I have seen a high voltage version of the LM317 that can do up to 60Vin, I may try to use that if I have to, but we're trying not to have to modify this board any more to fit the extra components required for an adjustable regulator.
Does anyone have any ideas? We may be able to use a 3 pin buck regulator chip, provided it has a reasonably clean output.
-Robby





RE: Need a 40V input rated version of the lm7815 regulator.
Sounds like you might end up with a smoking crater in the board anyway. Dumping 50% of the raw voltage on the regulator will usually try to roast things.
If your 15V load current is fairly fixed you can proceed the regulator with a power resistor to skim off half the voltage on a 'dumb' part instead of toasting the semiconductor regulator. That will remove voltage that would otherwise be 'seen' be the regulator. You could then stick with the LM7815.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need a 40V input rated version of the lm7815 regulator.
Gunnar Englund
www.gke.org
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RE: Need a 40V input rated version of the lm7815 regulator.
RE: Need a 40V input rated version of the lm7815 regulator.
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RE: Need a 40V input rated version of the lm7815 regulator.
We were thinking of using a 30V zener diode to bring the voltage back down, though it would be nice if we didn't need to. We shall find out tomorrow!
RE: Need a 40V input rated version of the lm7815 regulator.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Need a 40V input rated version of the lm7815 regulator.
Z
RE: Need a 40V input rated version of the lm7815 regulator.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need a 40V input rated version of the lm7815 regulator.
Otherwise, use a zener as suggested, or even put another 7815 with a 15V zener in the ground leg (makes for a 30 volt regulator) ahead of the 7815 for the 15V. The first 7815 with a ~30V output will drive people unfamiliar with the circuit crazy.
I had a similar situation for a simple low current supply running from 28VDC down to 12 V which needed to withstand 2 msec transients up to 88V, so I just put a TL783 (100V rating) regulating down to 24 volts, and then a 7812. The TL783 runs out-of-regulation sometimes with insufficient input to output headroom when the 28V input is at absolute minimun but it has done the job for several years in a product. Could have also used a zener regulated pass transistor to drop the voltage as well.
RE: Need a 40V input rated version of the lm7815 regulator.
The TPS7A4901DGNR is a low drop out linear reg with very good PSRR across a wide bandwidth. it is designed to be put on the output of a switcher to knock down the switcher noise. I'm using one on a TIA with over 120 dB of gain and power supply noise is not an issue.
Z
RE: Need a 40V input rated version of the lm7815 regulator.
The TPS7A4901DGNR that I found on digikey can only handle up to 35V and since this is a through-hole board it would be rather awkward to jumper in the 8 pin SMT package.
I pulled the 15V regulator out of the board on order to use a separate 15V lab power supply to measure the current draw. The circuit draws 200mA at max load. Also I tested a few of our zener's in stock and the best onewe had was only 1.3W at like 3.3W which just wouldn't cut it.
What we did instead was we found a drop in replacement buck regulator on digikey:
http://www.recom-power.com/pdf/Innoline/R-78HBxx-0...
Now I'm currently in the process of probing the board and trying to catch any issue that may be caused by the switching transients on the power rails.
RE: Need a 40V input rated version of the lm7815 regulator.
And Rob thanks for showing us that absurd part by an unknown company! I shall put that PDF in my "interesting parts" directory. It could come in handy someday.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need a 40V input rated version of the lm7815 regulator.
I'll be taking a better look at the switching transients on the rails tomorrow to see if they're causing me any issues. So far I'm really enjoying the 96% efficiency and not needing a heatsink.
RE: Need a 40V input rated version of the lm7815 regulator.
No doubt you would need some resistors in series to balance the Voltage.
RE: Need a 40V input rated version of the lm7815 regulator.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need a 40V input rated version of the lm7815 regulator.