AN8029 查看數據表（PDF） - Panasonic Corporation

零件编号

产品描述 (功能)

生产厂家

AN8029

Self-excited RCC pseudo-resonance type AC-DC switching power supply control IC

Panasonic Corporation 

Voltage Regulators

AN8029

s Application Notes (continued)

[1] Operation descriptions (continued)

3. Power supply output control system (FB : Feedback)

The constant voltage control of the power supply output is achieved by fixing the off-period of the power

MOSFET and changing the on-period. The control of on-period is performed by changing the charge current from

the TON terminal to the C3 through the following process: The photocoupler connected to the FB terminal (pin

9) absorbs, from the FB terminal, the feedback current corresponding to the output signal of the output voltage

detection circuit provided in the secondary side output. A current approximately 7 times of the current flowing out

of the FB terminal flows out of the TON terminal as the charge current for the C3. (Refer to figure 3.)

1:7

200 Ω

PC

Secondary side

power supply output

AN1431T/M

PC C3 C2

R2

Primary side Secondary side

Figure 3. Power supply output control system

The higher the AC input voltage of the current becomes, or the smaller the load current becomes, the larger the

current flowing out of the FB terminal becomes. When the current flowing out of the FB terminal becomes larger,

the charging to C3 becomes faster and the on-period becomes shorter.

In addition, the system has cancellation capability of about 180 µA for the dark current of the photocoupler.

(Refer to figure 4.)

ITON (mA)

−10

−8

−6

−4

−2

Dark current

0

− 0.2

− 0.4

− 0.6

− 0.8

−1.0

IFB (mA)

Figure 4. Feedback current versus charge current characteristics

4. Pseudo-resonance operation (Power MOSFET turn-on delay circuit)

For the AN8029, the pseudo-resonance operation becomes possible by making connection as shown in figure 5.

The C7 is a resonance capacitor, and the R9 and C9 constitute the delay circuit for regulating the turn-on of power

MOSFET. When the power MOSFET is turned off, the voltage generated in the drive coil is inputted to the TDL

(time delay) terminal (pin 1) through the R9 and C9. While high-level signal (higher than threshold voltage 0.32

V) is inputted, the power MOSFET remains off. Also, the TDL terminal has the high/low side clamping capabil-

ity. The upper limit of clamping voltage is 2.8 V typical (when sink current: 3 mA) and the lower limit of clamping

voltage is approximately 0 V (typical) (when source current: 3 mA). The off-period of the power MOSFET is

determined by the following periods whichever longer: The time until the TDL terminal input voltage becomes a

voltage lower than the threshold voltage as the transformer started the resonance operation and the drive coil

voltage drops, and the minimum off-period TOFF(min) of the internal oscillation circuit. (Refer to description on the

oscillation circuit.)

7

Share Link: