Need "noise free" boost regulator

Thread Starter

Mikrogut

Joined Aug 30, 2013
20
Hi,

I need a 5V/500mA boost regulator that can give me 5V from a 3.7V Li-Ion battery. Currently I am using the L6920 together with a 18uH inductor. The problem with the current solution is noise and ripple. I can hear a high frequently squealing from the inductor when the regulator is loaded. In addition there is +/-60mV ripple on the 5V output. I want a small ripple and I don't want to hear the conductor squealing.

Any suggestions for a 5V/500mA boost regulator that I can use instead?
 

Sensacell

Joined Jun 19, 2012
2,450
Find one with a higher switching frequency.

1) You will not hear it

2) the ripple frequency will be higher and easier to filter.
 

alfacliff

Joined Dec 13, 2013
2,449
are you using a store bought inductor, or homemade? if homemade, or exposed windings, coat it in epoxy, that will stick the windings down and prevent vibrations. for the ripple, use a ceramic cap to filter out the ripple, using the shortest leads possible.
 

AnalogKid

Joined Aug 1, 2013
8,107
That is true. Also, Linear Tech has some specialty dc/dc controllers optimized for low noise. But relatively high output noise is a common characteristic of all boost converters. Consider a second inductor as part of an extra output filter stage.

That's a good group of capacitor values, but as mentioned above capacitor type and placement have as much or more to do with performance than value. Also, pcb layout is critical. Follow the demo board if you can - they usually are optimized to make the part look as good as it can get. In particular, pay attention to any traces near (or under) the inductor.

ak
 

ronv

Joined Nov 12, 2008
3,768
My 2 cents. I think your inductor is a little small and the current rating a little low. It may be saturating at high current. A little LC circuit or more capacitance at the output should fix the ripple. But for fun sign up for web bench (TI) and look at some of their designs. I just did one below for a couple bucks in parts and 1 mv ripple.
 

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Thread Starter

Mikrogut

Joined Aug 30, 2013
20
How about using TPS61230 or TPS61027 from TI? They work at a higher frequency and require smaller inductors. That might help me removing the hearable squealing from my current solution.

I don't know how the 5V ripple would be, but it can't be much worse than now.
 

Papabravo

Joined Feb 24, 2006
12,405
I only draw about 200mA@5V from this regulator, so I don't think I am overloading the regulator or inductor.
You don't think or you know for certain? In an SMPS it is not unusual for the inductor current to be much greater than the output current. Thin wire or the wrong kind of core material and the inductors could very easily saturate.
 

THE_RB

Joined Feb 11, 2008
5,430
Agreed. Just use a bigger inductor.

At a low average current of 200mA it's not going to be critical for DC ohms etc so there is no need to use such a small inductor.

Larger inductor means less current ripple, and a larger output cap means less voltage ripple per load.
 
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