jaygunn
Active member
I am looking at creating a fairly standard bipolar IC-regulated PSU with very good ripple rejection. Of course schematics for these are readily available, e.g.:
http://www.jlmaudio.com/ACDCVer2sch.pdf
http://www.tnt-audio.com/clinica/regulators_noise2_e.html
http://www.beatbazar.com/guests/ssltech/kps-1/index.htm
http://web.telia.com/~u31617586/#48 volt phantom power supply
This one is edited from the one on JLM Audio's site. I have a couple of specific questions I'd appreciate help with.
Q1: Do we really need major ripple reduction on the INPUT to the LM317? I have seen as much as 6,600uF (where C5 and C6 sit in this schematic), and as little as 0.1uF. When I read TI's datasheet for the LM317 it specs ripple as a function of temp, output current and output voltage, but NOT as a function of input ripple.
The reason I care is that very big values of C5/C6 puts a big demand on the bridge diodes and I am thinking of using FRED diodes there instead of the usual IN4007.
Q2: One of the stated benefits of regulation is low PSU impedance. I am tempted to add one or more L-C filters after the PSU, like the following, for extra cleanliness. The question is whether the added series resistances of these filters greatly increases PSU impedance and do I care?
Suppose I put two L-C stages with 10R resistors and 1000uF caps after the
regulator output, maybe bypassed with 1uF tants. Any problems? Maybe slow ramp-up (which seems like a benefit to me) or huge current through the regulator (which might be fatal?),
This PSU would be used in a separate chassis to supply DC to 4 channels of mic pre and 4 channels of compression (2 pico, 2 Forssell opto). I'll provide +-24VDC and +-18VDC from one PSU and +-15VDC and +-12VDC from another in the same box, using 2 perf-boarded PSUs of the same general design. So load will vary according to which devices are in use.
Q3: Is it important whether the optional extra L-C filtering is physically placed on the PSU board in its chassis or on the preamp or compressor board in its separate box? I.e. close to the PSU or close to the ICs that are using the power? Of course all ICs in the preamps and compressors have local bypass caps that can help supply instantaneous demands for extra current.
John
http://www.jlmaudio.com/ACDCVer2sch.pdf
http://www.tnt-audio.com/clinica/regulators_noise2_e.html
http://www.beatbazar.com/guests/ssltech/kps-1/index.htm
http://web.telia.com/~u31617586/#48 volt phantom power supply
This one is edited from the one on JLM Audio's site. I have a couple of specific questions I'd appreciate help with.
Q1: Do we really need major ripple reduction on the INPUT to the LM317? I have seen as much as 6,600uF (where C5 and C6 sit in this schematic), and as little as 0.1uF. When I read TI's datasheet for the LM317 it specs ripple as a function of temp, output current and output voltage, but NOT as a function of input ripple.
The reason I care is that very big values of C5/C6 puts a big demand on the bridge diodes and I am thinking of using FRED diodes there instead of the usual IN4007.
Q2: One of the stated benefits of regulation is low PSU impedance. I am tempted to add one or more L-C filters after the PSU, like the following, for extra cleanliness. The question is whether the added series resistances of these filters greatly increases PSU impedance and do I care?
Suppose I put two L-C stages with 10R resistors and 1000uF caps after the
regulator output, maybe bypassed with 1uF tants. Any problems? Maybe slow ramp-up (which seems like a benefit to me) or huge current through the regulator (which might be fatal?),
This PSU would be used in a separate chassis to supply DC to 4 channels of mic pre and 4 channels of compression (2 pico, 2 Forssell opto). I'll provide +-24VDC and +-18VDC from one PSU and +-15VDC and +-12VDC from another in the same box, using 2 perf-boarded PSUs of the same general design. So load will vary according to which devices are in use.
Q3: Is it important whether the optional extra L-C filtering is physically placed on the PSU board in its chassis or on the preamp or compressor board in its separate box? I.e. close to the PSU or close to the ICs that are using the power? Of course all ICs in the preamps and compressors have local bypass caps that can help supply instantaneous demands for extra current.
John