Hwwigwh.Dlya-tIanStheegert4aUte.cdomGreen-Mode PWM Controller
Linearly decreasing PWM frequency
Burst-mode at light load and zero load
Low start-up current (20uA)
Low operating current (4mA)
Internal latch circuit for OTP, OVP
Built-in synchronized slope compensation
Totem pole output with soft driving
Constant power limit over a universal AC input
Current mode operation
Cycle-by-cycle current limiting
Under Voltage Lockout (UVLO)
Programmable PWM frequency
GATE output maximum voltage clamped at 18V
VDD Over Voltage Protection (OVP)
Programmable Over Temperature Protection (OTP)
Very few external components are required
General-purpose switch mode power supplies and
flyback power converters, including:
Battery Charger Adapter
The highly integrated SG6842 series of PWM
controllers provides several features to enhance the
performance of flyback converters. To minimize standby
power consumption, a proprietary green-mode function
provides off-time modulation to linearly decrease the
switching frequency under light-load conditions. Under
zero-load conditions, the power supply enters burst-mode.
This completely shuts off PWM output. Then, the output
restarts just before the supply voltage, VDD, drops below
the UVLO voltage. This green-mode function enables the
power supply to easily meet international power
For improved power conversion efficiency, the
SG6842 series is manufactured using the BiCMOS
process. This allows the start-up current to be reduced to
20uA, and the operating current to be reduced to 4mA.
For even higher power conversion efficiency, a large
start-up resistance can be used.
Built-in synchronized slope compensation ensures
the stability of peak current mode control. Proprietary
internal compensation ensures constant output power
limiting over a universal range of AC input voltages, from
90VAC to 264VAC.
SG6842 controllers provide many protection
functions. Pulse-by-pulse current limiting ensures a
constant output current, even when short circuits occur.
Should an open circuit failure occur in the feedback loop,
the internal protection circuit will disable PWM output.
PWM output will be disabled as long as VDD remains
higher than 26V. The gate output is clamped at 18V to
protect the power MOS from over-voltage damage. An
external NTC thermistor can be applied to sense the
ambient temperature for over temperature protection.
When either over temperature conditions or VDD over
voltage faults are detected, an internal latch circuit is used
to latch-off the controller. The latch will reset when the
temperature cools off sufficiently, or when the VDD
power supply is disabled.
SG6842 series controllers are available in both 8-pin
DIP and SO packages.
From bridge rectifier
D1 From auxiliary
© System General Corp.