Hi I am starting my first (bigger) DIY project box(spdif receiver/DAC/preamplifier). For powering opa627 I need +-15V supply and for powering other chips +5V or lower. After I made a research on the internet (mainly Power Supply for Preamps ) I came up with this schematics. In this power supply I was thinking about using Panasonic FC(35-50V) caps. One thing I still don't know if I would be okey with 2x18V 15VA toroidal transformer. Because it has 420ma supply per rail. I tried to roughly calculate how much current would be drawn by my box and excluding 3 voltage regulators seen in the schematics and two LDO regulators from texas instrumets for powering receiver and DAC. I've got that semiconductor parts: 8xopa627 (60mA), 2xBUF634 (40mA), cs8614 (11,8mA), wm8741 (95mA) and atmega8 should draw about ~25mA. So the total current on + rail would be 231,8mA if I am correct.
So any thoughts on this power supply or my chosen toroidal transformer are very welcome.
P.S. I want to get it right from the first time:]
So any thoughts on this power supply or my chosen toroidal transformer are very welcome.
P.S. I want to get it right from the first time:]
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The fuses should be located before the rectifiers.
You can add 10 to 100 uF capacitors across R2, R4 and R6, as mentioned in the datasheets for increased ripple rejection. They give a worthwhile performance increase.
I would feed the 5 V supply directly from the transformer to avoid loading the +15 V with 'digital' current. Using a double half bridge rectifier for this keeps the two windings on the transformer equally loaded as well. In other words feed the 5 V regulator from JP1 and JP4 via two rectifier diodes, cathodes tied together, like this:
http://upload.wikimedia.org/wikipedia/commons/5/5c/Fullwave.rectifier.en.svg
Keep the Gnd-Gnd connection.
Of course add a 1000 to 2200 uF filter capacitor at the input to the 5 V regulator.
You may find a small series resistor (1 ohm, 1-2 W) on the input side of each regulator useful to easily measure current when in use. Inserting this resistor between the 2200 uF filter capacitors also improves filtering a little bit.
You can add 10 to 100 uF capacitors across R2, R4 and R6, as mentioned in the datasheets for increased ripple rejection. They give a worthwhile performance increase.
I would feed the 5 V supply directly from the transformer to avoid loading the +15 V with 'digital' current. Using a double half bridge rectifier for this keeps the two windings on the transformer equally loaded as well. In other words feed the 5 V regulator from JP1 and JP4 via two rectifier diodes, cathodes tied together, like this:
http://upload.wikimedia.org/wikipedia/commons/5/5c/Fullwave.rectifier.en.svg
Keep the Gnd-Gnd connection.
Of course add a 1000 to 2200 uF filter capacitor at the input to the 5 V regulator.
You may find a small series resistor (1 ohm, 1-2 W) on the input side of each regulator useful to easily measure current when in use. Inserting this resistor between the 2200 uF filter capacitors also improves filtering a little bit.
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The secondary fuses achieve no added safety when fitted before the smoothing capacitors.
Fit a close rated mains fuse. That protects against the transformer and/or the rectifier and/or the smoothing capacitors going seriously faulty.
Added protection can be gained by fitting secondary fuses after the smoothing capacitance.
Fit a close rated mains fuse. That protects against the transformer and/or the rectifier and/or the smoothing capacitors going seriously faulty.
Added protection can be gained by fitting secondary fuses after the smoothing capacitance.
Hi Andrew,
I agree with the close-rated mains fuse.
However, with small transformers (<50 VA?) I do not trust any primary fuse to protect the transformer in case of rectifier or filter capacitor failure and add secondary fuses as a rule.
If the concern is to protect the regulators / audio circuits, then for sure add some fuses to each load after the main filter capacitors.
I agree with the close-rated mains fuse.
However, with small transformers (<50 VA?) I do not trust any primary fuse to protect the transformer in case of rectifier or filter capacitor failure and add secondary fuses as a rule.
If the concern is to protect the regulators / audio circuits, then for sure add some fuses to each load after the main filter capacitors.
Absolutely. This is my concern with small transformers. Some are inefficient enough that you can short the secondary indefinitely without the primary fuse blowing. If the transformer does not have an internal thermal fuse you could end up with a fire.
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