cupoftea
Advanced Member level 5
Hi,
Power integrations say that their TOPswitch-HX Flyback controller is voltage mode.
However, in their App Note, AN57, they give, on page 11, the Power Stage/Modulator transfer function for it.
This equation does not account for the ramp in the TOPswitch.
Therefore, TOPswitch cannot be a voltage mode controller...do you agree?
AN57 is in top post of this...
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This microsemi app note, on page 8, shows the Power stage and modulator transfer function for a voltage mode flyback (ok they give it for buckboost, but it is a derivative)
...As you can see, it contains the ramp parameter, which power integrations do not give in AN57....therefore, TOPswitch cannot be in voltage mode, do you agree?
...Aaaaagh...further in-looking shows that the equations contain a factor "KTOP", which is 0.2/mA, and referes to the change in duty cycle with error current...this , in effect, pertains to the RAMP situation....woops...sorry....still...is of interest i would have thought......so after all, it is in Voltage Mode.
...Actually, this post sheds some light on trying to demystify why the AN57 feedback loop equations give an unusual set of bode plots...
www.edaboard.com
...also, as to the use of a type 2 compensator to stabilise a voltage mode controller (TOPswitchO)....and there is no stipulation that the crossover frequency is far from the output stage LC resonance.
...if you stabilise a Voltage Mode controller with a type 2 compensator, then its pretty important that you apply constarints to the level of the crossover frequency...but AN57 says nothing of this......there is also the strange statement that the resonance frequency of the "effective sec inductance" with the output cap must be >500Hz.....this ends up giving you a hard limit on your choice of max output capacitance.
Power integrations say that their TOPswitch-HX Flyback controller is voltage mode.
However, in their App Note, AN57, they give, on page 11, the Power Stage/Modulator transfer function for it.
This equation does not account for the ramp in the TOPswitch.
Therefore, TOPswitch cannot be a voltage mode controller...do you agree?
AN57 is in top post of this...
TOPswitch-HX Flyback Feedback Loop?
Hi, We have just done this 20W Offline Flyback. (90VAC input, 24vout and 0.8A out) Transformer is np/ns = 84/19 and Lp = 1.07mH Its in CCM at 90VAC. TOPswitch-HX is voltage mode controller. We used AN57 to give the Bode plots. But they come out "nonsense" as the attached excel shows. Do you...
This microsemi app note, on page 8, shows the Power stage and modulator transfer function for a voltage mode flyback (ok they give it for buckboost, but it is a derivative)
...As you can see, it contains the ramp parameter, which power integrations do not give in AN57....therefore, TOPswitch cannot be in voltage mode, do you agree?
--- Updated ---
...Aaaaagh...further in-looking shows that the equations contain a factor "KTOP", which is 0.2/mA, and referes to the change in duty cycle with error current...this , in effect, pertains to the RAMP situation....woops...sorry....still...is of interest i would have thought......so after all, it is in Voltage Mode.
--- Updated ---
...Actually, this post sheds some light on trying to demystify why the AN57 feedback loop equations give an unusual set of bode plots...
Voltage mode CCM flyback cannot be done with type 2 compensator?
The TOPswitch flyback controller is a voltage mode flyback controller by Power integrations. It is the single most popular offline flyback controller in the world in terms of number of different SMPS’s that use it. It is a superb part, so why does app note 57 by Power integrations (attached)...
...also, as to the use of a type 2 compensator to stabilise a voltage mode controller (TOPswitchO)....and there is no stipulation that the crossover frequency is far from the output stage LC resonance.
--- Updated ---
...if you stabilise a Voltage Mode controller with a type 2 compensator, then its pretty important that you apply constarints to the level of the crossover frequency...but AN57 says nothing of this......there is also the strange statement that the resonance frequency of the "effective sec inductance" with the output cap must be >500Hz.....this ends up giving you a hard limit on your choice of max output capacitance.
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