Hi All,
I made a DC power supply board to power my Dac. The topology is as follows:
+15V: 5V input from USB Charger -> TPS61085 DC to DC converter (+17V) -> LM2941 Regulator (+15V) -> Output
-15V: 5V input from USB Charger -> TPS61085 DC to DC converter (+17V) -> Charge Pump (-16.5V) -> LM2991 Regulator (-15V) -> Output
I measured the output voltage with a DMM (that's the only test equipment I have), and the result were as per design. However, when turning the power on, I heard a constant noise (not very loud, but audible within a few ft. from the board). Note that the board is not connected to any load, just 5V power from USB charger. Not sure how to describe the noise, but it does not sound like whining noise, but a bit like rapid mechanical vibration. I did not pay too much attention to it at that time. To me surprise, when I connected the power supply to the dac and the rest of the system, I hear a kind of wideband noise at the speakers. It sounds like random radio / TV noise, or gentle rain hitting at the roof. At a volume level setting that usually gives 70-80dB SPL, I could hear it faintly at my listening position about 9 ft. away from the speakers.
I don't get this noise when using a different power supply that uses AC transformer and LDO. So it is quite obvious that the noise appeared because of this power supply. I do not have a lot of knowledge / experience in electronics. Just attempted to design and implement a DC power supply after doing some research on the internet. The circuit is done based on recommendations in the datasheets of the switcher and ldo. I think I must have missed some very important design rules.
1. Can anyone have a look at the schematics and shed some light on what could have gone wrong?
2. I did not have separate ground planes for the switcher and ldo. Would it help if they use separate ground planes? If yes, how should the ground planes be connected, e.g. using ferrite bead / capacitor?
Best regards
Liu
I made a DC power supply board to power my Dac. The topology is as follows:
+15V: 5V input from USB Charger -> TPS61085 DC to DC converter (+17V) -> LM2941 Regulator (+15V) -> Output
-15V: 5V input from USB Charger -> TPS61085 DC to DC converter (+17V) -> Charge Pump (-16.5V) -> LM2991 Regulator (-15V) -> Output
I measured the output voltage with a DMM (that's the only test equipment I have), and the result were as per design. However, when turning the power on, I heard a constant noise (not very loud, but audible within a few ft. from the board). Note that the board is not connected to any load, just 5V power from USB charger. Not sure how to describe the noise, but it does not sound like whining noise, but a bit like rapid mechanical vibration. I did not pay too much attention to it at that time. To me surprise, when I connected the power supply to the dac and the rest of the system, I hear a kind of wideband noise at the speakers. It sounds like random radio / TV noise, or gentle rain hitting at the roof. At a volume level setting that usually gives 70-80dB SPL, I could hear it faintly at my listening position about 9 ft. away from the speakers.
I don't get this noise when using a different power supply that uses AC transformer and LDO. So it is quite obvious that the noise appeared because of this power supply. I do not have a lot of knowledge / experience in electronics. Just attempted to design and implement a DC power supply after doing some research on the internet. The circuit is done based on recommendations in the datasheets of the switcher and ldo. I think I must have missed some very important design rules.
1. Can anyone have a look at the schematics and shed some light on what could have gone wrong?
2. I did not have separate ground planes for the switcher and ldo. Would it help if they use separate ground planes? If yes, how should the ground planes be connected, e.g. using ferrite bead / capacitor?
Best regards
Liu
Perhaps the discontinuous conduction mode on the TPS61085 spraying noise all over the audio band - fixed frequency switchers that don't use discontinuous conduction mode only produce significant power in the harmonics of the switching frequency, not sub harmonics which might be what you are seeing. Looks distinctly dodgy basing the charge-pump voltage inverter on discontinuous mode too. Might be worth trying extra LC filtering at the output and shielding the whole switch-mode part.