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Author Topic: Switching power sounds noisy  (Read 955 times)
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I created a small PCB design using a switching power supply part number TPS61200DRCR with a 4.7uH inductor LQH3NPN4R7N0L. The inductor is rated at over an amp but but design only draws 40mA. For some reason the supply sounds  very noisy. When I blink and LED I can actually hear the supply on every blink. Today I'll view the output on a scope to see if it measures noisy as well. The input and output capacitors are all the correct values according to the data sheet. Has anyone ever seen this before?
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I created a small PCB design using a switching power supply part number TPS61200DRCR with a 4.7uH inductor LQH3NPN4R7N0L. The inductor is rated at over an amp but but design only draws 40mA. For some reason the supply sounds  very noisy. When I blink and LED I can actually hear the supply on every blink. Today I'll view the output on a scope to see if it measures noisy as well. The input and output capacitors are all the correct values according to the data sheet. Has anyone ever seen this before?
Switching Power Supply design is an art unto itself.  Little things like parts placement, component alignment, ESR of capacitors, connection lengths, wire/pcb techniques, all affect the supply and its operating characteristics.
Without pictures, exact part numbers and a schematic of the design, it is unlikely someone here, or anyone else could help you.  These are very specialized skills.
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The data sheet shows the recommended parts placement. On my design I ended up putting the capacitors on the opposite side of the board. That's most likely my problem. For the next boards I'll follow the data sheets recommendations.
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That is the way to go.  Good Luck!
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I'm planning to use almost that exact same part in a project that I am doing it.  It is the 3.3V fixed output voltage version TPS61201DRCR.  How did you go about soldering that part to your board?
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Did you use ceramic caps, if so what were their temperature coefficient (X7R, Z5U, etc.)
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I have a voltage divider set for 5 volts. A fixed one would probably save me two resistors. The part is hand soldered using a microscope so the components GND pad under the part is not soldered to the board. Pins #4 and #9 are both GND and run to the center GND pad on the boards so I just hand solder those two pins.
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I used ceramic caps and just used whatever temperature type I could find since it will always be in a room temperature environment. Most likely X7R type. Nice. Thats something I never though of. I'll check that out as well.
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All class 2 and 3 dielectrics will sing.   X7R and X5R the least.  Z5U and Y5V the worse.

Switch to a "better" (if you aren't already using X7R) dielectric or go to the highest rated voltage you can.  
« Last Edit: January 09, 2013, 11:19:26 am by James C4S » Logged

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You may not be loading the power supply enough. 1 amp and 40mA is quite a difference. The power supply may want a little more load.

The other problem is that the power supply may not be running at a high enough switching frequency. A good switching supply runs at frequncies outside the range of human hearing.
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