 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
AN4137 Datasheet(PDF) 10 Page - Fairchild Semiconductor |
|
||||||||||||||||||||||||||||||
AN4137 Datasheet(HTML) 10 Page - Fairchild Semiconductor |
|
|
10 / 20 page  AN4137 APPLICATION NOTE 10 ©2003 Fairchild Semiconductor Corporation and RB is the internal feedback bias resistor of FPS, which is typically 2.8k Ω and R 1, RD, RF, CF and CB are shown in fig- ure 12. Figure 13. CCM flyback converter control-to output trans- fer function variation for different input voltages Figure 14. CCM flyback converter control-to output trans- fer function variation for different loads Figure 15. DCM flyback converter control-to output trans- fer function variation for different loads When the input voltage and the load current vary over a wide range, it is not easy to determine the worst case for the feed- back loop design. The gain together with zeros and poles vary according to the operating condition. Moreover, even though the converter is designed to operate in CCM or at the boundary of DCM and CCM in the minimum input voltage and full load condition, the converter enters into DCM changing the system transfer functions as the load current decreases and/or input voltage increases. One simple and practical way to this problem is designing the feedback loop for low input voltage and full load condi- tion with enough phase and gain margin. When the converter operates in CCM, the RHP zero is lowest in low input volt- age and full load condition. The gain increases only about 6dB as the operating condition is changed from the lowest input voltage to the highest input voltage condition under universal input condition. When the operating mode changes from CCM to DCM, the RHP zero disappears making the system stable. Therefore, by designing the feedback loop with more than 45 degrees phase margin in low input voltage and full load condition, the stability over all the operating ranges can be guaranteed. The procedure to design the feedback loop is as follows (a) Determine the crossover frequency (fc). For CCM mode flyback, set fc below 1/3 of right half plane (RHP) zero to minimize the effect of the RHP zero. For DCM mode fc can be placed at a higher frequency, since there is no RHP zero. (b) When an additional LC filter is employed, the crossover frequency should be placed below 1/3 of the corner fre- quency of the LC filter, since it introduces a -180 degrees phase drop. Never place the crossover frequency beyond the corner frequency of the LC filter. If the crossover frequency is too close to the corner frequency, the controller should be designed to have a phase margin greater than 90 degrees when ignoring the effect of the post filter. (c) Determine the DC gain of the compensator (wi/wzc) to cancel the control-to-output gain at fc. (d) Place a compensator zero (fzc) around fc/3. (e) Place a compensator pole (fpc) above 3fc. Figure 16. Compensator design v FB ˆ v o1 ˆ --------- - w i s ----- 1s w zc ⁄ + 11 w pc ⁄ + --------------------------- ⋅ = (35) where w i R B R 1RDCF ----------------------- , w zc 1 R F R 1 + ()C F --------------------------------- , w pc 1 R BCB --------------- = = = 0 dB 20 dB -20 dB -40 dB 40 dB 10Hz 100Hz 10kHz 1kHz 1Hz 100kHz Low input voltage High input voltage f p f p f z f z f rz frz 0 dB 20 dB -20 dB -40 dB 40 dB 10Hz 100Hz 10kHz 1kHz 1Hz 100kHz Heavy load Light load f p f p f z f rz f rz 0 dB 20 dB -20 dB -40 dB 40 dB 10Hz 100Hz 10kHz 1kHz 1Hz 100kHz Heavy load Light load f p f p f z f z 0 dB 20 dB -20 dB -40 dB 40 dB 10Hz 100Hz 10kHz 1kHz 1Hz 100kHz Control to output f p f z f rz Compensator Loop gain T f zc f pc f c |
Similar Part No. - AN4137 |
|
Similar Description - AN4137 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
