MT7930 查看數據表（PDF） - Unspecified

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MT7930

Single Stage, High PFC, AC-DC LED Driver

Unspecified 

Maximizing IC Performance

MT7930

Single Stage, High PFC, AC-DC LED Driver

waveform information, as the auxiliary winding

voltage is proportional to the output voltage

(secondary winding voltage) during the OFF time

period. The auxiliary winding voltage is sampled

by DSEN pin, one LEB (Leading Edge Blanking)

time right after DRV signal is turned off.

Fig.1 Start up sequence

DRV

Power Factor Correction

The primary side current increases linearly from

zero to peak value, as sensed by the current

sensing pin CS, during the external MOSFET

on-time. When the primary current reaches the

threshold, MT7930 turns off the power MOSFET

immediately. After a constant OFF time, TOFF,

MT7930 turns on the power MOSFET again. The

peak current threshold is regulated by MAXIC

proprietary technique and follows the rectified

sinusoidal-shape of main line voltage. As a result,

the envelope of the inductor current is

sinusoidal-shaped, high power factor is therefore

achieved in this way.

Fig.2 Power Factor Correctioin

Auxiliary Sensing

MT7930 features over-voltage protection (OVP),

short-circuit protection (SCP), and over-current

protection (OCP) functions. Those protections

are triggered by sensing the auxiliary winding

Aux

LEB time

Fig.3 Auxiliary Signal Sensing

Over-voltage Protection

MT7930 is implemented with two over-voltage

protection schemes: (1) If DSEN pin’s voltage is

detected above 3.2V for three times (refer to

Auxiliary Sensing section), MT7930 turns off

the PWM switching signal, and VDD voltage

gradually drops to UVLO threshold, and the

system will be re-started. The threshold voltage

of over-voltage protection VOUT_OV, can be easily

defined as (refer to the application circuit in page

1):

VOUT_OV



3.2  (1

R5) 

R6

Ns

Na

VD8

Where Ns is the secondary winding, Na is

auxiliary winding, VD8 is the forward bias of the

secondary side rectifier diode.

(2) If VDD pin’s voltage exceeds 19.2V three

times, MT7930 turns off the PWM switching

signal, and VDD gradually drops to UVLO

MT7930 Rev. 1.30

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