AND8039 View Datasheet(PDF) - ON Semiconductor

Part Name

Description

Manufacturer

AND8039

The One-Transistor Forward Converter

ON Semiconductor 

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 –20 dB/decade

continuous slope. Then one can calculate the amount of

mid–band gain that the error amplifier must provide to

“push–up” or “lower” the gain function so that the crossover

frequency is set at 8.0 kHz. This is done by:

Gxo + 20 Log(fxońffp) ) GDC + )18.2 dB

converting this value to absolute gain for later use:

Axo + 10[Gxoń20] + )8.13

Now one can begin to calculate the actual error amplifier

feedback component values.

C5 + 1ń2pfxoAxoR11 + 360 pF

R4 + AxoR11 + 56 K ohms

C6 + 1ń2pfezR4 + 0.56 mF

+80

+60

+40

Control–to–Output

+20

Light Load

0

1.0

10

–20

–40

–60

–80

Control–to–Output

0

Light Load

–90

Closed Loop

100

1.0K

10K

100K

1M

Rated Load

–180

–270

Error Amp

Rated Load

–360

Figure 4. Compensation Bode Plots for the Example

http://onsemi.com

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