ld7578h Leadtrend Technology, ld7578h Datasheet - Page 13

• Manufacturer Part Number: ld7578h
• Description: High Voltage Green-mode Pwm Controller With Over Temperature Protection
• Manufacturer: Leadtrend Technology

By using this dual-oscillator control, the green-mode
frequency can be well controlled and further to avoid the
generation of audible noise.
Over Load Protection (OLP)
To protect the circuit from the damage during over load
condition or short condition, a smart OLP function is
implemented in the LD7578H. Figure 17 shows the
waveforms of the OLP operation.
condition, the feedback system will force the voltage loop
toward the saturation and then pulls the voltage of COMP
pin to high. Whenever the VCOMP trips the OLP
threshold 5.0V and continues over 125mS (when
switching frequency is 65KHz), the protection is activated
and then turns off the gate output to stop the switching of
power circuit. The 125mS delay time is to prevent the
false trigger from the power-on and turn-off transient. The
over load protection is latch off mode. User should
remove AC power source. The Vcc of LD7578H will drop
down and de-latch until the Vcc of LD7578H lower than
PDR level.
A divide-2 counter is implemented to reduce the average
power under OLP behavior. Whenever OLP is activated,
the output is latched off and the divide-2 counter starts to
count the number of UVLO(off).
the 2nd UVLO(off) point is counted then the output is
recovery to switching again.
By using such protection mechanism, the average input
power can be reduced to very low level so that the
component temperature and stress can be controlled
within the safe operating area.
Leadtrend Technology Corporation
LD7578H-DS-00 February 2010
The latch is released if
Under such fault
www.leadtrend.com.tw
13
OVP (Over Voltage Protection) on Vcc
The V
mostly with 30V maximum. To prevent the V
condition, LD7578H is implemented with OVP function on
Vcc. As long as the the Vcc voltage is higher than the
OVP threshold voltage, the output gate drive circuit will be
shutdown simultaneous thus to stop the switching of the
power MOSFET until the next UVLO(
The Vcc OVP function in LD7578H is latch off type
protection. If the OVP condition, usually caused by the
feedback loop opened, is tripped, the Vcc will not recover
until AC power turn off . Figure 18 shows its operation.
The Vcc of LD7578H will drop down due to AC power turn
off. The de-latch level of OVP is determined by internal
PDR. Over voltage protection could be released soon as
Vcc is below PDR level.
UVLO(off)
UVLO(on)
PDR
5.0V
VCC
COMP
OUT
GS
Switching
ratings of the nowadays power MOSFETs are
125mS
OLP
Non-Switching
OLP Counter Reset
2nd UVLO(off)
OLP trip Level
Fig. 17
LD7578H
AC power off
De-latch
ON
).
Switching
GS
from fault
t
t
t