MC34262D 查看數據表（PDF） - ON Semiconductor

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MC34262D

Power Factor Controllers

ON Semiconductor 

MC34262, MC33262

10mA

Error

Amp

+

R2

1

R1

6

2

C1

Figure 26. Error Amp Compensation

The Error Amp output is a high impedance node and is susceptible to noise pickup. To minimize pickup, compensation

capacitor C1 must be connected as close to Pin 2 as possible with a short, heavy ground returning directly to Pin 6. When

operating at high ac line, the voltage at Pin 2 may approach the lower threshold of the Multiplier, ≈ 2.0 V. If there is

excessive ripple on Pin 2, the Multiplier will be driven into cut−off causing circuit instability, high distortion and poor power

factor. This problem can be eliminated by increasing the value of C1.

7

7

Current

Sense

Comparator

22k

4

R

10pF

C

R7

Figure 27. Current Waveform Spike Suppression

A narrow turn−on spike is usually present on the leading edge of

the current waveform and can cause circuit instability. The

MC34262 provides an internal RC filter with a time constant of

220 ns. An additional external RC filter may be required in

universal input applications that are above 200 W. It is

suggested that the external filter be placed directly at the Current

Sense Input and have a time constant that approximates the

spike duration.

Current

Sense

Comparator

22k

4

10pF

D1

R7

Figure 28. Negative Current Waveform

Spike Suppression

A negative turn−off spike can be observed on the trailing edge of

the current waveform. This spike is due to the parasitic

inductance of resistor R7, and if it is excessive, it can cause

circuit instability. The addition of Schottky diode D1 can

effectively clamp the negative spike. The addition of the external

RC filter shown in Figure 26 may provide sufficient spike

attenuation.

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