Hello,
Looong time lurker here and it's finally time to come forward for help, so thank you in advance!
I have built a microphone preamp that requires +24VDC, ~100mA. The power supply for it is +/-16VDC, 3A. The power supply is a standard 317/337 dual regulated circuit that has powered multiple pieces of gear over the years.
I implemented an LM2585 DC-DC converter to boost the +/-16VDC to +28VDC, then I regulated the voltage down to +24VDC using an LM7824. The circuit I used is straight off of the data sheet, Fig. 50 on page 19:
http://www.ti.com/lit/ds/symlink/lm2585.pdf
One of these pre amps work fine, even two or three but any more than that and the positive rail shuts down and goes into about 3.5VDC, the negative rail holds strong at -16VDC. I'm not overloading the supply current wise as I always stay under half an amp and well within the supply's limits.
The negative rail is connected to the pre amp but goes to a 47uf 63V electrolytic to ground.
Since there is no load on the negative rail is the positive rail losing some sort of common reference? Since the positive and negative rail are regulated separately I don't see why they would affect each other.
I don't have schematics unfortunately, my bad habits in design. The power supply and mic pre work just fine until I use the DC-DC booster and even then I only see a problem when I have multiple pre's with the booster circuit being powered by the same supply. I'm fairly confident in everything except how advisable it is to only use the positive rail and basically ignore the negative rail.
My main question is if it is harmful to the power supply to have this unit loading only the positive rail and ignoring the negative rail?
I hope that isn't too disjointed of a question and there is enough info to help you get an idea of what's going on.
THANKS!!
Daniel
Looong time lurker here and it's finally time to come forward for help, so thank you in advance!
I have built a microphone preamp that requires +24VDC, ~100mA. The power supply for it is +/-16VDC, 3A. The power supply is a standard 317/337 dual regulated circuit that has powered multiple pieces of gear over the years.
I implemented an LM2585 DC-DC converter to boost the +/-16VDC to +28VDC, then I regulated the voltage down to +24VDC using an LM7824. The circuit I used is straight off of the data sheet, Fig. 50 on page 19:
http://www.ti.com/lit/ds/symlink/lm2585.pdf
One of these pre amps work fine, even two or three but any more than that and the positive rail shuts down and goes into about 3.5VDC, the negative rail holds strong at -16VDC. I'm not overloading the supply current wise as I always stay under half an amp and well within the supply's limits.
The negative rail is connected to the pre amp but goes to a 47uf 63V electrolytic to ground.
Since there is no load on the negative rail is the positive rail losing some sort of common reference? Since the positive and negative rail are regulated separately I don't see why they would affect each other.
I don't have schematics unfortunately, my bad habits in design. The power supply and mic pre work just fine until I use the DC-DC booster and even then I only see a problem when I have multiple pre's with the booster circuit being powered by the same supply. I'm fairly confident in everything except how advisable it is to only use the positive rail and basically ignore the negative rail.
My main question is if it is harmful to the power supply to have this unit loading only the positive rail and ignoring the negative rail?
I hope that isn't too disjointed of a question and there is enough info to help you get an idea of what's going on.
THANKS!!
Daniel
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