Flyback in DCM vs CCM?

[grizedale]

Why is a flyback in Discontinuous mode easier to control than a flyback in continuous mode?

 

[mtwieg]

Discontinuous mode means you won't have a RHP zero, or any subharmonic oscillation in current mode control. Also you get input power limiting via volt-time product limiting.

 

[grizedale]

is it also because a DCM flyback can ALWAYS be stabilised by reducing the gain of the compensation error amplifier?.....whereas a CCM flyback may go unstable if the error amp gain is either increased or decreased?

 

[mtwieg]

Well anything can be stabilized if you lower the loop gain enough.... but in general yes a DCM flyback will be easier to compensate because it only has a single pole, even in voltage mode control. It should never have problems with conditional stability (unless it starts operating in continuous mode).

 

[grizedale]

yes i agree anything can be stabilised of you lower the loop gain enough.......................but..........

for example with a CCM flyback, there is a point, where if you decrease the gain, you can go through an unstable patch......due to the dipping of the phase of the power stage.......though as you rightly imply, if you keep decreasing the loop gain, you go right through this and become stable again.

...the above doesnt happen with DCM...because at any bandwidth where you have stability....reducing the gain also gives stability.