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Power supplies are needed for every type of electronic equipment and are one of the most important component in a audio electronic equipment such as a DAC.
This project illustrate how can you build a simple low cost unregulated power supply that you can use for a DAC that have an unregulated power supply input from 15V to 18V and a current < 1500mA.
The circuit
The circuit is very simple and have low ripple and low noise. The power trasformer must be at least 45VA with a secondary voltage of 15V.
The circuit is powered by turning ON main power switch S1 and is overcurrent protected by fuse F1 250V - 200mA slow-blow type. The first capacitor C1 is a X2 type 250V and helps to reduce high frequency noise component wich comes from the 230V power mains. The transformer TR1 is a 45VA with primary at 230V and secondary at 15V AC. The capacitor C2 reduce high frequency noise. The diode bridge rectifier B1 is a 6A current rated KBL608.
Low pass filter network
The decoupling network is a second order RC low pass filter. This network decreases noise transmission of the high-frequency content of any current that does pass through the resistor. The series elements are 2 small value resistors and DC voltage drop is acceptable because the current is low.
With resistors value R1 = R2 = 0.47 Ohm and capacitors value C3 + C4 = C5 + C6 = 4800uF, the 2nd order RC Low-pass filter have:
|
2nd order RC Low-pass filter |
||
|
Center frequency |
fc |
77.5 Hz |
|
Q factor |
Q |
0.33 |
Technical specifications
The table below see you the measured value in real working condition of the power supply I have designed versus the original one from AUNE AUDIO equipped with AUNE USB DAC MKII SE.
|
Characteristics |
ADPSLAB Simple Low Ripple PSU for DAC |
Original AUNE power supply Model: MINI -- 1501 |
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AC Main Input |
230V - 50Hz |
230V - 50Hz |
|
Trasformer |
45VA 230Vpri - 15Vsec |
|
|
DC Votage Output (unloaded) |
20.2V (measured value) | 22.8V (measured value) |
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DC Voltage Output (with 500mA load) |
17.6V (measured value) | 17.6V (measured value) |
|
DC Current Output (max) |
1.5A | 1A |
The table below see you the measured value in real working condition of my AUNE USB DAC MKII SE.
| AUNE USB DAC MKII SE Power Requirements | ||
|
DC Current Absorbed (min) |
USB playback working condition with Headphone Load and Volume to minimum | 130mA at 19.2V (measured value) |
|
DC Current Absorbed (max) |
USB playback working condition with Headphone Load and Volume to maximum | 300mA at 18.5V (measured value) |
Final Test
I have measured the Ripple/Frequency values of the original Original AUNE power supply Model: MINI -- 1501 and my ADPSLAB Simple Low Ripple PSU for DAC with a constant current load of 500mA. The figure below show the tests result. The tests values comes from the FFT results of oscilloscope measurements.
Bibliography
Some information, material and related graphics available on this page are provided by web sites below. This are only for informational use.
OKAWA Electric Design - 2nd order CR Low-pass Filter Design Tool - http://sim.okawa-denshi.jp/en/CRCRtool.php
Power Supply Noise Reduction - Ken Kundert - http://www.designers-guide.org/Design/bypassing.pdf
Linear Power Supply Design - Rod Elliott - http://sound.westhost.com/power-supplies.htm
