TY72011 查看數據表（PDF） - ON Semiconductor

零件编号

产品描述 (功能)

生产厂家

TY72011

Single Ended PWM Controller Featuring QR Operation and Soft Frequency Foldback

ON Semiconductor 

TY72011AP2

If we now enter this formula into a spreadsheet, we can easily plot the switching frequency versus the output power demand:

250000

200000

150000

Fmax

100000

Transition

BCM to VFM

Fmax

50000

VCO Action

0

0

5

10

15

20

OUTPUT POWER (W)

Figure 4. Free Running Frequency vs. Output Power

The typical above diagram shows how the frequency

moves with the output power demand. The components used

for the simulation were: Vin = 300 V, Lp = 6.5 mH,

Vout = 10 V, Np/Ns = 12.

The red line indicates where the maximum frequency is

clamped. At this time, the VCO takes over and decreases the

switching frequency to the minimum value.

VCO Operation

The VCO is controlled from the Verr voltage. For Verr

levels above 1.0 V, the VCO frequency remains unchanged

at 125 kHz. As soon as Verr starts to decrease below 1.0 V,

the VCO frequency decreases with a typical small-signal

slope of -175 kHz/mV @ Verr = 500 mV down to

zero (typically at FB ≈ 3.3 V). The demagnetization

synchronization is however kept when the Toff expands.

The maximum switching frequency can be altered by

adjusting the Ct capacitor on pin 5. The 125 kHz maximum

operation ensures that the fundamental component stays

external from the international EMI CISPR-22

specification beginning.

The following drawing explains the philosophy behind

the idea:

Internal Verr

VCO Frequency

is Fixed at 130 kHz

VCO Frequency

can Decrease

BCM Mode

Peak current

can change

Peak Current is Fixed

3V

1V

0.75 V

Figure 5.

http://onsemi.com

8

Free Datasheet http://www.datasheet-pdf.com/

Share Link: