Hello,
Greetings to all that read this. I am modding my current PSU design to add a 5v output. I have a few questions concerning the best way to design it.
Basic details:
Toroidal TRX 50va 36v / CT
OUTPUT 1 = 48v supply from TRX sec. Charge pump to TL783 + misc
OUTPUT 2/3 = +/- 18v from full wave rect. CRC - 7818 / 7918 +misc
Output 4 = sub tap after 18v bridge diode. - Dropping R - 7812
Now to the needed 5v. This will pull about .5 - 1 Amp so should I just run another bridge rect. off the TRX sec, then filter (CRC?) then just 7805 it? I mean that would work, but wondering if there is a smarter way than just multi tapping 1 transformer with various 78XX regs?
See attached PDF. The proposed 5v supply is on the top just glued onto everything else
Greetings to all that read this. I am modding my current PSU design to add a 5v output. I have a few questions concerning the best way to design it.
Basic details:
Toroidal TRX 50va 36v / CT
OUTPUT 1 = 48v supply from TRX sec. Charge pump to TL783 + misc
OUTPUT 2/3 = +/- 18v from full wave rect. CRC - 7818 / 7918 +misc
Output 4 = sub tap after 18v bridge diode. - Dropping R - 7812
Now to the needed 5v. This will pull about .5 - 1 Amp so should I just run another bridge rect. off the TRX sec, then filter (CRC?) then just 7805 it? I mean that would work, but wondering if there is a smarter way than just multi tapping 1 transformer with various 78XX regs?
See attached PDF. The proposed 5v supply is on the top just glued onto everything else
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Assuming the center tap of the transformer is grounded, the bridge rectifier is shorting out each side of that transformer for half the cycle so this will just blow a fuse or the bridge rectifier. You can cut the negative pin on D16 or remove D16 and just connect to the + pin on D7.
Since you have a such a high voltage (~25VDC) to waste in order to get down to 5V, you should buy a buck converter module from Amazon etc. (cheap and simple) as a pre-regulator if not the whole 5V regulator. The buck converter will give you 25/5 times the 5V current that you draw from the 25VDC, and very little heat.
Since you have a such a high voltage (~25VDC) to waste in order to get down to 5V, you should buy a buck converter module from Amazon etc. (cheap and simple) as a pre-regulator if not the whole 5V regulator. The buck converter will give you 25/5 times the 5V current that you draw from the 25VDC, and very little heat.
Wind a few turns, measure & compute turns needed.
That's what I did on a PA in order to get rid of the two voltage dropping resistors for the pre-amp which were wasting heat.
Thank you. I thought about this, but was concerned about noise on the +/- 18v rails as these are audio power supplies. None issue?
It depends on the added loading vs added capacitor filtering. You could include a blocking diode to prevent the 5V system from loading the 18V capacitors.
But unless the 5V drain is very small, you should definitely use a buck converter for the 5V. A cheap possibility is to use the guts of a auto-USB adapter.
But unless the 5V drain is very small, you should definitely use a buck converter for the 5V. A cheap possibility is to use the guts of a auto-USB adapter.
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