Denon DRA-F107 Service Manual page 38

3 Functional Description
3.1 Power Management
R
VCC
Power Management
Undervoltage
Lockout
13.5V
8.5V
Power-Down
Reset
Power-Up
Reset
6.5V
R
Soft-Start
SoftS
T1
C
Soft-Start
Figure 6 Power Management
The Undervoltage Lockout monitors the external
supply voltage V . In case the IC is inactive the
VCC
current consumption is max. 55μA. When the SMPS is
plugged to the main line the current through R
charges the external Capacitor C
exceeds the on-threshold V
circuit and the voltage reference are switched on. After
that the internal bandgap generates a reference
voltage V =6.5V to supply the internal circuits. To
REF
avoid uncontrolled ringing at switch-on a hysteresis is
implemented which means that switch-off is only after
active mode when Vcc falls below 8.5V.
In case of switch-on a Power Up Reset is done by
resetting the internal error-latch in the protection unit.
When V falls below the off-threshold V
VCC
internal reference is switched off and the Power Down
reset let T1 discharging the soft-start capacitor C
at pin SoftS. Thus it is ensured that at every switch-on
the voltage ramp at pin SoftS starts at zero.
Main Line (100V-380V)
Start-Up
Primary Winding
C
VCC
Internal
Bias
6.5V
5.3V
Voltage
4.8V
Reference
4.0V
R Q
PWM-Latch
S Q
Error-Latch
Soft-Start Comparator
Error-Detection
Start-up
. When V
VCC
=13.5V the internal bias
CCon
=8.5V the
CCoff
Soft-Start
DRA-F107 / DRA-F107DAB
3.2 Improved Current Mode
Soft-Start Comparator
FB
PWM Comparator
0.8V
PWM OP
Improved
Current Mode
Figure 7 Current Mode
Current Mode means that the duty cycle is controlled
by the slope of the primary current. This is done by
comparison the FB signal with the amplified current
sense signal.
Amplified Current Signal
FB
0.8V
Driver
VCC
T
on
Figure 8 Pulse Width Modulation
In case the amplified current sense signal exceeds the
FB signal the on-time T
resetting the PWM-Latch (see Figure 8).
The primary current is sensed by the external series
resistor R inserted in the source of the integrated
Sense
CoolMOS™. By means of Current Mode regulation, the
38
Functional Description
PWM-Latch
R Q
S Q
x3.65
Isense
of the driver is finished by
on
Driver
t
t