How to use the soft-start function of UCC3895

timewentby

Other Parts Discussed in Thread: UCC3895

I've designed a 2400W ZVS full bridge and choose the UCC3895 as my PWM controller.(Voltage Controlled Mode)
I want to add the soft-start function to my control circuit but I am confused about how to realize it.

For soft-start , is it direct connect with a pair of resistor and capacitor paralleled in pin 19 to ground?

By the way since I have used a optical voltage sensor as the isolated circuit so I direct connected my PI controller signal into my UCC3895 (the Error amp connected as the voltage follower)
Is this the right way to accept error signal ?

Control circuit
http://i.imgur.com/KNktU2b.png

over 9 years ago

0 John Stevens over 9 years ago

TI__Expert 7395 points

I will have someone from the high power team take a look here.
Regards
John

0 timewentby over 9 years ago in reply to John Stevens

Prodigy 30 points

Thank you .I'd really appreciate it.

0 Colin Gillmor over 9 years ago in reply to timewentby

TI__Mastermind 25570 points

You are correct, a parallel RC combination from SS/DISB (Pin 19) to GND will give you a soft start function. The SS time is set by this RC combination and the charging current out of the SS/DISB. The charging current is set by the value of the resistor at the RT pin (see P11 of the datasheet).

I have not used this component personally but your use of the optical voltage sensor sounds correct to me - do make sure that you are getting negative feedback rather than positive feedback.

Regards

Colin

0 timewentby over 9 years ago in reply to Colin Gillmor

Prodigy 30 points

Thanks for your generous reply, I will soon give it a try

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How to use the soft-start function of UCC3895