Forward /Flyback Converter Control Theory

[ricky4u]

Hello,

I am designing 300W power supply. Did design it with the help of data sheet and field application engineer. Need some basic support/documents which can be helpful to understand control theories behind it. How poles and zeroes are useful to operate properly and how to select them in feedback.

Thanks!!
Ricky

 

[DCPreamp]

Some helpful information...

I'm not sure precisely what you're looking for by "poles and zeros," but I figure you're talking about feedback techniques, frequency response, and -3dB poles. Attached is an application note from National Semiconductor I think might do the trick.

Also look at control IC datasheets and application notes. They usually have specific information for closed-loop feedback control pertaining to the IC. Check out SG3524/25/26, TL494, UC3842/2/4/5, etc.

Other experts on this forum might be able to give you better insight into your question if you gave details about your project and desired outcome. Details such as the control method, the input/output voltages and currents, the need for isolation, safety requirements, transformer and core specifics, etc.

Best of luck, and I hope to have helped you just a tad...

 

[ricky4u]

Thanks for the reply.

I am designing half bridge forward converter with the help of fairchild IC FAN4800 and driver FAN7382. Specs are 90/135 VAC to 20VDC/13 Amps. Taking help from fairchild engineers. It is quite understandable to get values from Datasheets (attachment). But what is going inside the IC to control the output is still not clear to me.

Many factors has been considered to control duty cycle like output voltage/ Rectified voltage/ Current/ PFC voltage etc. How this values are being handle inside the IC (control circuit) is what i am trying to understand. I have attached calculation i did for my circuit aswell. Also for other people who wants to know something about control few links are as belwo.

PWM:
1) http://www.youtube.com/watch?v=Zep3ikgHutU
2) http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/square.html#c1

Links shows some basics of PWM. But for better current control Inductor current waveform will be used as a ramp to the circuit. And then after Amplifier type 1/2/3, RHP "0" all this thing starts appearing. I try to get some idea by reading but lost. Looking for some basic understanding how all this factors are playing role in duty cycle calculation and how the 3dB frequency and some other elements are decided.

THanks Again !!!