UCC2800D for flyback converter

Hi Yuquan,

Is there a particular reason why the UCC2800 is been chosen for the flyback application. We have newer dedicated flyback controllers with more design collateral available, such as LM5023, UCC287xx series, UCC28630.

Regards

Peter

Hi There:

The reason is that it is known UCC2800 works very well in industry. We are sure about that.

I would assume the design principle should be the same for other similar controller.

Thanks

Y.L

Hi Yuquan,

This link, http://www.ti.com/lit/ml/slup261/slup261.pdf describes the design procedure for a flkyback power stage.

One point to consider is that the UCC2800 will not have any feature to ensure low no-load power and the avergage mode efficency requirements may be more challenging to meet with this controller.

Regards

Peter

Hi There:

I only understand system level design now. Any material regarding how to determine voltage feedback resistor and current sensing resistor's resistance value, input /out put inductance value, turn ratio? power/current sourcing  capability ? these are the key design parameters.

Thanks

Y.L

Hi Y.L

There are worked examples for DCM and CCM flyback transformer designs in this article that may be of some use.

http://www.google.de/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&uact=8&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.ti.com%2Flit%2Fml%2Fslup127%2Fslup127.pdf&ei=3UxGVKb9E4Gd7gbB8IDgAQ&usg=AFQjCNG0PB2nNkTJ8pr7iCTfTL2GLsPXwA&bvm=bv.77880786,d.ZGU

Regards

Peter

Thanks. 

We understand PWM feedback control well, though not for fly back converter specifically.

We also have top level understanding of fly back converter working principle. 

The difficult /key thing is how to determine the amount of feedback voltage  and feedback current and the

corresponding reference voltage and reference current for feedback control purpose.

Would like to learn form example with more details.

Thanks

Y.L

Hi Y.L

Try this link which will bring you to the TI Power Seminar archive. There may be something in here that will help you.

http://www.smps.us/Unitrode2.html

Regards

Peter

Hi There:

Is there any free software or tables to help design fly back converter with peak current PWM controller?

Thanks

Y.L

Hello:

Regarding  UCC2800 data sheet for fly back converter design

(1) On page1 it says, Reference voltage is 5V. Does that mean REF pin will have 5 Volt output voltage?

(2) ON Page2 the block diagram, over current  is 1.5V, does that mean when the voltage across current sensing resistor reaches 1.5V threshold, the PWM will be off?

(3) VCC description:

Page 4 says max will be 12 V applied. Page 6 Note says VCC will be setting at 10V. SO, what is the minimum VCC we can apply?

Thanks

On more question

Regarding  UCC2800 data sheet for fly back converter design,

Page 7 says: "COMP is the output of the error amplifier and the input of the PWM comparator."

Since it is an output, do we need it in fly back converter  feedback loop design ?

Thanks

Hi Yuquan,

Yes the REF pin produces a 5V reference.

The typical setpoint for the Over Current Threshold is 1.55V above this level the PWM gate drive will be terminated.

Vcc min is determined by the turn off threshold and depends on which part number from the UCC2800 family is selected for the application, see table on page 1. The maximum Vcc voltage is 12V.

In an isolated flyback design the error amplifier function is normally implemented using a compensated TL431 on the secondary side. The Opto-coupler transistor can then drive the COMP directly bypassing the internal error amplifer section in the UCC2800.

This link may be useful to design a number of topologies

http://www.ti.com/tool/powerstage-designer?keyMatch=power design tools&tisearch=Search-EN

Regards

Peter

The data sheet says COMP is the output of the error amplifier and the input of the PWM  comparator.

If it is an output of the error amplifier, why do we need to drive it? Do we need to drive it with secondary output feedback voltage?

Thanks

Y.L