Switchmode design

Hello experts,

I am learning switchmode design and I have been wondering:

Are there any disadvantages from using a bigger coil than the minimum? The formulaes most often say "larger than or equal to", so the cost and space issues aside, what would be the downside from using large uH values, where low uH values would normally suffice?

Thank you for your answer`s.

Best regards Henrik

Reply to
Henrik [7182]
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Hi Henrick,

it's mainly about the cost and size, larger inductor value will result less output ripple and reduce the core loss. Too large an inductor value results in added expense and may impede load transient responses because it reduces the effect of slope compensation.(current mode regulators).

yours Ren

Reply to
tomrei

'Hi Henrick, ' 'it's mainly about the cost and size, larger inductor value will result 'less output ripple and reduce the core loss. 'Too large an inductor value results in added expense and may impede 'load transient responses because it reduces the effect of slope 'compensation.(current mode regulators).

'yours Ren

assuming a buck regulator.

yup, going rediculously large (say an order of magnitude) for the inductors will sacrifice load transient response simply because it takes longer for the inductor to change it current level in response to the change in load level.

It does some good things though like make the ripple current smaller in the output caps. be carefull with DIY inductors. The more turns you put the higher the capacitince and you start gettng thin spikes on the output.

Reply to
mook johnson

Also note that in current mode switchers, you're comparing the inductor current to some setpoint, and the ripple current in the inductor relative to its average value is effectively the signal to noise ratio that the current comparator sees. If that SNR is low (due to very low ripple -- a larger inductor), it can cause some jitter in the switch's duty cycle and hence make the output a little bit noisier. Some data sheets specify a recommended minimum ripple current to avoid this problem.

Truth be told, though, many switchers seem to jitter a bit and it's not much of a problem in the real world. But if you're looking to reproduce those textbook waveforms, you might be disappointed.

Reply to
Joel Koltner

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