Question: continuous and discontinuous-conduction mode

continuous conduction mode

in SMPS,there are two modes : continuous and discontinuous-conduction modes, the explain in book is
"The continuous-conduction mode is defined by continuous output current over the entire switching period,whereas the discontinuous conduction mode is defined by discontinuous output current during any portion of the switching period"
I don't really understand, anyone can describe in detail ?

thanks a lot


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chmr

discontinuous conduction mode

They are talking about the current in the output inductor or transformer. In the discontinuous mode the output capacitor supplies the load current when the inductor current is zero.

continuous current conduction

Hi,

Usualy switching power suppliers feed load through inductor and capacitor.

Buck power suppliers - through inductor when switch is ON, and through inductor and capacitor when switch is OFF.

Boost power suppliers - through capacitor when switch is ON, and through inductor and capacitor when switch is OFF.

Continious Current Mode (CCM) means that current through inductor flows continuously throughout the switching period (always >0).

Discontinuous Current Mode (DCM) means that current through inductor reaches zero before the end of the switching period (when switch is OFF).
At this time capacitor feeds load.

In most regulators applications CCM is used.
But Boost and flyback circuits have problem with loop compensation.

DCM is often used for lower load current applications.

b/rgds

understand continuous conduction mode in smps

uladz55 said:

Hi,

DCM is often used for lower load current applications.

b/rgds

Click to expand...

What is the level of current can you give some typical values for lower current ?

continuos conduction mode

it depends on your SMPS topology; there are two type of topologies:forward mode and flyback mode.
for forward mode , the value is considered 10% of the maximum current (full load); more value leads to lower frequency rsponse of the feedback loop and higher value leads to higher output ripple.
flyback mode usually are designed to be in discontinous mode at full load or low value of continous mode, this makes the feedback loop stable, otherwise there will be a RHP zero which is hard to cope in feedback design process!
refer to A. Pressman book for more details.

BEST!

flyback dcm ccm ti

1. DC-DC conveters can change CCM to DCM depend on load.
You can check the criterion here.
**broken link removed**

The example is here
http://www.linear.com/pdf/1937f.pdf

2.Sometimes you can chose DCM for all loads.
Check this paper


http://focus.ti.com/lit/ml/slup058/slup058.pdf


best regards