12-28-2018, 05:17 AM
There's another power architecture I'd like to suggest - multiple regulation. Basically:
(1) Start out with a DC supply of somewhere around 12 volts, capable of delivering as much amperage as your system will need (probably 2-3 amps).
(2) Use two or more separate linear regulators to down-regulate this 12 volts, to the 5 volts needed by the various modules.
(3) Pay attention to how you do the power grounding.
I built a player like this earlier this year, using a Pi 2, a HAT-sized prototyping card, and a generic I2S DAC card with a PCM510x DAC chip. The high-voltage supply is a 12-volt 3-amp switching-type "power brick" which plugs into the back of the player case. The DC wiring goes to a 7805-type TO-220 regulator (a mil-spec variant I had handy) that's bolted to the bottom of the case - this provides 5 volts to the Pi, via the HAT card and the power/ground pins on the header. The 12 volts also runs over to the corner of the HAT card, where I have a 78L05 regulator (a little TO-92 part) which then supplies the DAC module soldered to the HAT prototyping area.
Both of the 5-volt regulators have bypass caps on their inputs and outputs, to provide local decoupling and ensure stable operation.
I think this approach has a lot of advantages. The use of two separate regulators helps isolate the DAC from any power-supply "surge" noise introduced by the Pi (and the DAC module has its own low-dropout regulator which increases the isolation still further).
i was a bit concerned about whether a single 7805-type regulator could handle the current demands of a Pi 2, considering that it's dropping 6-7 volts across the regulator and could (worst case) dissipate quite a few watts of heat. So far it's had no problem... neither the case nor the regulator has gotten more than barely warm to the touch, and I haven't had any unstable operation or crashes. Considering that the Pi cores are about 95% idle during playback of my Ogg Vorbis collection, the low power usage makes good sense. One could always use a heftier 5-volt regulator, or parallel two of them, or use a hybrid regulator (a 7805 with an outboard pass transistor to do the heavy lifting) if one wanted.
There's a way to gild the lily here that I haven't tried... pre-filtering the 12-volt input to the 5-volt regulators even further, using a capacitance multiplier. With a single transistor (or Darlington), a modest-sized cap, and a couple of resistors, one can create an extremely "stiff" voltage buffer which would greatly attenuate any switching noise from the 12-volt "brick" before it got to the 5-volt regulators.
A similar approach ought to work out well for any Pi setup using a DAC that has independent provisions for power input.
(1) Start out with a DC supply of somewhere around 12 volts, capable of delivering as much amperage as your system will need (probably 2-3 amps).
(2) Use two or more separate linear regulators to down-regulate this 12 volts, to the 5 volts needed by the various modules.
(3) Pay attention to how you do the power grounding.
I built a player like this earlier this year, using a Pi 2, a HAT-sized prototyping card, and a generic I2S DAC card with a PCM510x DAC chip. The high-voltage supply is a 12-volt 3-amp switching-type "power brick" which plugs into the back of the player case. The DC wiring goes to a 7805-type TO-220 regulator (a mil-spec variant I had handy) that's bolted to the bottom of the case - this provides 5 volts to the Pi, via the HAT card and the power/ground pins on the header. The 12 volts also runs over to the corner of the HAT card, where I have a 78L05 regulator (a little TO-92 part) which then supplies the DAC module soldered to the HAT prototyping area.
Both of the 5-volt regulators have bypass caps on their inputs and outputs, to provide local decoupling and ensure stable operation.
I think this approach has a lot of advantages. The use of two separate regulators helps isolate the DAC from any power-supply "surge" noise introduced by the Pi (and the DAC module has its own low-dropout regulator which increases the isolation still further).
i was a bit concerned about whether a single 7805-type regulator could handle the current demands of a Pi 2, considering that it's dropping 6-7 volts across the regulator and could (worst case) dissipate quite a few watts of heat. So far it's had no problem... neither the case nor the regulator has gotten more than barely warm to the touch, and I haven't had any unstable operation or crashes. Considering that the Pi cores are about 95% idle during playback of my Ogg Vorbis collection, the low power usage makes good sense. One could always use a heftier 5-volt regulator, or parallel two of them, or use a hybrid regulator (a 7805 with an outboard pass transistor to do the heavy lifting) if one wanted.
There's a way to gild the lily here that I haven't tried... pre-filtering the 12-volt input to the 5-volt regulators even further, using a capacitance multiplier. With a single transistor (or Darlington), a modest-sized cap, and a couple of resistors, one can create an extremely "stiff" voltage buffer which would greatly attenuate any switching noise from the 12-volt "brick" before it got to the 5-volt regulators.
A similar approach ought to work out well for any Pi setup using a DAC that has independent provisions for power input.
