UC3843 boost stability

[elektrojack]

Hi everyone,
i need help to ensure the maximum gain and the stability of my boost converter.

My boost operates with a freq of 100kHz and a inductor of 400uH.

the out voltage is about 430v set by the divider at output.

the peak of current in the inductor is 5amps and it is set by the sense resistor of a 0.2ohm.

My application consists to charge a 2.5uF capacitor at 430v in about 3.5ms, and discharge it in 0.5ms, so i must charge and discharge it at 250hz (4ms of period).

So i want understand what is the compensation network between pins 1 and 2 of uc3843 for my purpose.

Thanks

 

[MacGyverS2000]

What does the datasheet say?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Comcokid]

That's why they make spice programs.

 

[elektrojack]

Hi, the datasheet says to ad a pole of a freq fp=1/(2*pi*Cf*Rf)
at the same freq of the zero introduced by the esr of the output filter capacitor.

Cf and Rf are between the pin 1 and 2.

I don't know the esr of the capacitor, but i know that the capacitor is in series with a primary winding of AT coil (because this is a CDI system), and i know the resistance of the coil, about 1 ohm.

So i think the esr is small respect the resistance of the coil, and i must take this value for place the right pole.

right?

 

[MacGyverS2000]

How do you not know the esr of the cap? It's right in the datasheet for the component...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[elektrojack]

I don't found the datasheet of the cap.

however if i have the cap in series with an inductor (primary winding of a coil) and the inductor have a resistance of about 1ohm, i can neglect the esr of the cap because is smaller than the resistance of the coil. Right?


thanks

 

[OperaHouse]

Without knowing the particulars I can still say two things. Anyone with good equipment knows that the ESR of most caps is quite bad and for that reason the manufacturers do not publish the ESR in datasheets. It is unlikely the SR of the cap is less than the resistance of the coil.

 

[MacGyverS2000]

You do understand the difference between DC resistance (coil of wire) and AC resistance (cap), right?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[elektrojack]

The dcr is the resistance in dc conditions and esr is the resistance in high frequency conditions.

I measured the esr of the cap, about 140mohm at 100khz with an lcr meter.

This is the connection of the output stage of the boost.