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This my 12V boost converter shematic and Vin voltage 6.6V to 8.4V. I use Texas Instruments LM3478 boost converter.

I calculated my capacitor value, resistor value, inductor value, switching frequency etc. with formulas in the datasheet. This shematic works fine when the 12 V current is bigger than 10 mA, but when current lower than 10 mA I hear a voice in inductance. I analyzed it with osciloscope and there is no gate drive.

  1. i can add a resistor to 12V like 2k2 ohm, but my V in batary, i dont want power loss.
  2. i think maybe, its capacitor esr problem.
  3. i can add a mosfet Vin and i can switch it when current bigger than 10mA. But i must change my firmware, shematic and pcb.

Also I have search this problem and i found discontinues mode. But i dont know how can i change my shematic.

LM3478 Datasheet enter image description here

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    \$\begingroup\$ You need a bleeder/minimum load. \$\endgroup\$ – winny Dec 20 '16 at 21:12
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    \$\begingroup\$ Also, what is the output voltage and FB pin during this event? If you need no-load performance, you need to be looking at a skip mode/burst mode controller. \$\endgroup\$ – winny Dec 20 '16 at 21:19
  • \$\begingroup\$ thanks @winny this one of my solution, may be i change my adc resistor value less than 22k and 6k8 \$\endgroup\$ – Sercan Coban Dec 20 '16 at 21:27
  • \$\begingroup\$ thanks for reply @winny when no load, Vout 12V also its stabil and feedback voltage is right \$\endgroup\$ – Sercan Coban Dec 20 '16 at 21:29
  • \$\begingroup\$ So no problem then. You can "cheat" and just lower the impedance of your feedback divider network to sink current there if you don't want to add another resistor. But again, if no load consumption is a concern, you need a skip mode controller. \$\endgroup\$ – winny Dec 21 '16 at 7:07
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You hearing voice in your head or from other places they shouldn't be is a medical issue, not a electrical engineering one.

However, this buck controller is inappropriate for applications where the load might get very light or go to zero. Note that the on time for the switch is at least 210 ns. It also seems that this device uses a fixed frequency. I didn't read every word of the datasheet (that's your job), but didn't see mention of pulse skipping, and it's pretty clear the frequency doesn't get changed.

If you need to support very low load currents, then use a controller that can switch between PWM and PFM, or do cycle skipping. It appears this one doesn't.

You could add a resistor to always guarantee the minimum required load current, but that's really a hack working around having the wrong controller in the first place.

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