ld7578 Leadtrend Technology, ld7578 Datasheet - Page 13

• Manufacturer Part Number: ld7578
• Description: Green-mode Pwm Controller With Hv Start-up Circuit And Otp Protection
• Manufacturer: Leadtrend Technology

When the V
typical), LD7578 will shutdown the gate output and then
latch the power supply off unless either Vcc drops below
8V (power down reset) or V
cooled down, rises over a threshold voltage about 1.05V.
Accordingly, there are two methods to restart the circuit:
one is to cool down the circuit for recovery and the other
to re-plug the AC power. The detailed operation is
depicted as figure 19.
Pull-Low Resistor on the Gate Pin of
MOSFET
An anti-floating resistor is implemented in the OUT pin to
prevent any uncertain output, which may cause MOSFET
working abnormally or false triggering-on.
such design won’t cover the conditions of disconnection of
gate resistor R
resistor connected at the MOSFET gate terminal (as
Leadtrend Technology Corporation
LD7578-DS-00 October 2008
UVLO(on)
UVLO(off)
PDR (8V)
AC input Voltage
1.05V
0.95V
V
(-)Latch
VCC
OUT
Switching
OTP
(-)LATCH
G
. It is still strongly recommended to have a
falls below the threshold voltage (0.95V
OTP Release
Non-Switching
Fig. 19
AC Off
(-)LATCH
Latch Released
, as the temperature is
AC On (Recycle)
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However,
Switching
t
t
t
t
13
shown in figure 21) to provide extra protection for fault
conditions.
This external pull-low resistor is to prevent the MOSFET
from being damaged during power-on when the gate
resistor is disconnected. In such a single-fault condition,
as shown in figure 22, the resistor R8 can provide a
discharge path to avoid the MOSFET from being
false-triggered by the coupling through the gate-to-drain
capacitor C
be pulled low to maintain MOSFET in an off-state no
matter the gate resistor is disconnected or opened in any
case.
GD
. Therefore, the gate of MOSFET should
Fig. 20
LD7578