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AND8039 Datasheet, PDF (6/12 Pages) ON Semiconductor – The One-Transistor Forward Converter | |||
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AND8039/D
The crossover frequency will be set at about 8.0 kHz. To
accomplish this, one assumes that the eventual closed loop
bode gain response of the system will be â20 dB/decade
continuous slope. Then one can calculate the amount of
midâband gain that the error amplifier must provide to
âpushâupâ or âlowerâ the gain function so that the crossover
frequency is set at 8.0 kHz. This is done by:
Gxo + 20 Log(fxoÅffp) ) GDC + )18.2 dB
converting this value to absolute gain for later use:
Axo + 10[GxoÅ20] + )8.13
Now one can begin to calculate the actual error amplifier
feedback component values.
C5 + 1Å2pfxoAxoR11 + 360 pF
R4 + AxoR11 + 56 K ohms
C6 + 1Å2pfezR4 + 0.56 mF
+80
+60
+40
ControlâtoâOutput
+20
Light Load
0
1.0
10
â20
â40
â60
â80
ControlâtoâOutput
0
Light Load
â90
Closed Loop
100
1.0K
10K
100K
1M
Rated Load
â180
â270
Error Amp
Rated Load
â360
Figure 4. Compensation Bode Plots for the Example
http://onsemi.com
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