transient response and upper feedback divider resistor in smps

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grizedale

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Hi

we do 350W offline half bridge. vac = 90-265.

Vout is 50v.

Its so high vout that we have large value upper feedback divider resistor.

will we get beter transient response if we use lower value upper feedback divider resistor and just put up with the increased dissipation in this resistor?
 

Hi. yes, you can have a better transient respond if you used a lower resistance at upper feedback of a divider resistor. But its divided voltage may increase beyond your reference value.
 
Lower feedback network impedance will move one of the poles to the right,
increasing bandwidth some if that is a limiting factor (I would suspect not,
if you are talking tens of kOhm and tens of pF).

Shunting that upper resistor with a small C and/or RC series, gives you
feedforward compensation and tweaking that can get you a lot of
improvement in step response.
 
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