Is Topswitch based flyback SMPS in current mode or voltage mode?

F

Flyback

Well-Known Member

• Mar 6, 2016

• #1

What do you think?
Is Topswitch-jx a Current mode, or a Voltage mode controller?

Topswitch datasheet:
https://ac-dc.power.com/sites/default/files/product-docs/topswitch-jx_family_datasheet.pdf


(Topswitch is a PWM controller for offline flyback SMPS's)

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Mar 6, 2016

• #2

There is a current source symbol on D in Figure 3. (Top right of the block diagram) Thus, I suspect current based.

 

F

Flyback

Well-Known Member

• Mar 6, 2016

• #3

Thanks, but that's just the start-up current source, it doesn't pertain to the mode of operation.

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Mar 6, 2016

• #4

Well, there is an Ifb on the left hand top side too.

 

F

Flyback

Well-Known Member

• Mar 6, 2016

• #5

yes, thanks, that the error signal, (its a current not a voltage as is often seen in other controllers), and it doesn't pertain to whether or not this is a voltage mode or a current mode flyback control chip

 

ronsimpson

Well-Known Member

Most Helpful Member

• Mar 6, 2016

• #6

I have used a number of the "switches" and find them interesting. (very cost effective)

I did not look at the .PDF but.....some parts look at the voltage across the closed MOSFET to measure current. So it is possible to have a current mode switcher with out a current sense resistor. Even with out an external current input pin.
also
It is possible to fake the current by watching time and the input voltage. So there is current mode and what I call fake current mode. LOL

 

F

Flyback

Well-Known Member

• Mar 6, 2016

• #7

if you were to look at page 4, fig6, it s seen that at around medium loading, it goes into a mode where it maintains the peak primary current level at about 55% of the maximum setting for current and then adjusts the off time as load varies. Is this called current mode or voltage mode?
From the feedback loop point of view, is it classed as current mode or voltage mode?

 

ChrisP58

Well-Known Member

Most Helpful Member

• Mar 7, 2016

• #8

I haven't read deeply, but from here: https://ac-dc.power.com/products/topswitch-family/

"The latest generation of our flagship TOPSwitch™ series of high efficiency integrated power conversion ICs is TOPSwitch-JX. TOPSwitch-JX incorporates a 725 V power MOSFET and full-featured, multi-mode controller to achieve excellent no-load performance and high efficiency across the entire load range."​

My guess is that maybe it runs in more than one mode, shifting gears as it's operating conditions change.