3.4 Standby Mode Control (patent applied for)
The MR2000 Series is able to switch between two methods
of output voltage control - normal operation and the standby
mode, in a single power supply.
The standby mode supported by this IC employs the burst
method for intermittent operation under light loads to
reduce oscillation frequency and switching losses, and is
effective in reducing the standby input voltage under
micro-loads.
A unique characteristic of this IC is the use of the burst
mode for intermittent operation without stopping IC control,
and thus minimizing output ripple.
The Z/C pin is clamped to a voltage of 4.5V (typical) or less
by an external signal to allow selection of standby mode
control. The standby mode is cleared (ie restored to the
normal mode) by clearing the clamp voltage on the Z/C pin,
and applying a voltage of 4.5V (typical) or higher.
In normal operation the ON range of the main switching
device is controlled in a linear manner in relation to voltage
variation at the F/B pin, while in standby mode operation the
Emitter/OCL pin current detection threshold value is
switched from 0.6V for the normal mode to 0.05V for the
standby mode.
The collector current is fixed at a peak value by the current
detection threshold value, and the burst mode is selected.
Burst mode control is such that oscillation occurs when the
voltage at the F/B pin is 1.8V (typical) or higher, and is
stopped when this voltage is 0.8V (typical) or lower.
Drain pin
7
Z/C pin
Emitter/OCL
pin
6
Switched from
0.6V to 0.05V
Output voltage error
detection feedback
signal
1
F/B pin
2
3
4.5V
(TYP)
Standby signal
(external signal)
Fig.3.5 Standby Mode Control
V
F/B(burst stop)
=0.8V
V
F/B(burst start)
=1.8V
【V
F/B
】
【I
C
】
【V
OUT
ripple】
As output voltage control in the standby mode fixes the
Fig.3.6 Standby Mode Control Sequence
drain current peak value for each oscillation cycle, the duty
ratio of the oscillating and non-oscillating intervals is varied to ensure a constant voltage.
Standby mode start
0.2V
4.5V(TYP)
Standby mode clear
【V
Z/C
】
【I
C
】
【I
OUT
】
Normal operation
Standby mode
Fig.3.7 Standby Signal Receive Sequence
Normal
operation
Shindengen Electric MFG.CO.,LTD
- 8 -
SHINDENGEN [ SHINDENGEN ELECTRIC MFG.CO.LTD ]
