### Author Topic: EEVblog #110 - Let's Design a DC to DC Switchmode Converter  (Read 2029 times)

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#### JonnyJacksonX

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##### EEVblog #110 - Let's Design a DC to DC Switchmode Converter
« on: March 26, 2016, 03:42:38 pm »
Hello.

I'm new to electronics and I need to make a step down circuit.
I want to design a bike led lamp feed by 3 18650 li ion battery, so 11.1V Vin.
Then I need to step down the voltage with a buck converter, as a linear converter seems to be really inefficient.
I find the #110 video from eevblog about the venerable MC34063.
For calculating the values of the in and out parts, like inductors, resistors, capacitor... I need use the frequency as a variable.
But, here is the issue, what is the frequency to use with a battery? Aren't the voltage a constant? The frequency is 0 (I know it's not)?

Thanks for answering my noob question. And sorry for the bad english.

#### Simon

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• Did that just blow up? No? might work after all !!
##### Re: EEVblog #110 - Let's Design a DC to DC Switchmode Converter
« Reply #1 on: March 26, 2016, 04:05:51 pm »
You have to pick a frequency you want to use, that is the frequency the chip will oscillate at. This comes with the knwledge that the higher the frequency the less efficient it may be but the smaller the parts. Just go for a ballpark 40KHz to get you going.

#### JonnyJacksonX

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##### Re: EEVblog #110 - Let's Design a DC to DC Switchmode Converter
« Reply #2 on: March 26, 2016, 04:44:25 pm »
well.

I didn't understanded that the frequency was about the IC, not the source of power. So I will use 40 kHz.

#### ghulands

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##### Re: EEVblog #110 - Let's Design a DC to DC Switchmode Converter
« Reply #3 on: April 03, 2016, 12:41:00 am »
well.

I didn't understanded that the frequency was about the IC, not the source of power. So I will use 40 kHz.