Thanks PRR
I have good stock of 1000uF, 2200uF, 4700uF, and 10,000uF, all in 25V or 35V.
I was pondering whether to use passive RC filtering.
I plugged values into PSUD2 and it looks like three 2.2 ohm 2W resistors in a CRCRCRC string would suffice to get 12.155Vrms DC with 2.1mV ripple:
DiodeBridgePositive--1000uF--2.2R--2200uF--2.2R--10,000uF--2.2R--10,000uF
In PSUD2, it looks like changing the value of C1 (the reservoir cap) raises/lowers the output voltage by a couple tenths of a volt. Larger values for C1 raise the peak current in the bridge rectifier (with 2200uF I see 7A peak, but 600mA RMS). I only have 3A rated Schottky diodes. Do I need to use a higher current rating? I have some big honkin' 20A bridge rectifiers, but I was hoping to use Schottky diodes.
If I increase C1 and C2 to 4700uF, the VDC rms out goes up to 12.4V and ripple falls to a miniscule 263uV. But peak current on the rectifier goes up to 7.85A with 690mA RMS. Does that mean I'd blow a bridge made of 3A Schottky rectifiers with such large values of C1 and C2?
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I have good stock of 1000uF, 2200uF, 4700uF, and 10,000uF, all in 25V or 35V.
I was pondering whether to use passive RC filtering.
I plugged values into PSUD2 and it looks like three 2.2 ohm 2W resistors in a CRCRCRC string would suffice to get 12.155Vrms DC with 2.1mV ripple:
DiodeBridgePositive--1000uF--2.2R--2200uF--2.2R--10,000uF--2.2R--10,000uF
In PSUD2, it looks like changing the value of C1 (the reservoir cap) raises/lowers the output voltage by a couple tenths of a volt. Larger values for C1 raise the peak current in the bridge rectifier (with 2200uF I see 7A peak, but 600mA RMS). I only have 3A rated Schottky diodes. Do I need to use a higher current rating? I have some big honkin' 20A bridge rectifiers, but I was hoping to use Schottky diodes.
If I increase C1 and C2 to 4700uF, the VDC rms out goes up to 12.4V and ripple falls to a miniscule 263uV. But peak current on the rectifier goes up to 7.85A with 690mA RMS. Does that mean I'd blow a bridge made of 3A Schottky rectifiers with such large values of C1 and C2?
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The "dot" denotes the beginning of the winding, thus the polarity.
If you're not going above 12V on a 317, it should be fine to use, however a 12-0-12ct is a better option
My rule for Silicon rectifiers is to be sure the datasheet headline on the diode is "greater than" the rated max current of the transformer.
(Which means if you need 1A and have a 10A transformer in-hand, you want 10A diodes.)
This is a practical observation. The real decision gets to the Peak rating of the diode and the DCR of the windings, and also how often you will power-up. At modern diode prices, in one-off builds, it is expedient to just pick diode "greater than" the rated max current of the transformer. When you build your market and start making millions of units, you want a sharper pencil and some brain-pain to shave the pennies.
(Which means if you need 1A and have a 10A transformer in-hand, you want 10A diodes.)
This is a practical observation. The real decision gets to the Peak rating of the diode and the DCR of the windings, and also how often you will power-up. At modern diode prices, in one-off builds, it is expedient to just pick diode "greater than" the rated max current of the transformer. When you build your market and start making millions of units, you want a sharper pencil and some brain-pain to shave the pennies.
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