MR1721 Datasheet PDF

MR1721 - Shindengen Electric

Part Number MR1721
Description Partial Resonance PS IC
Manufacturers Shindengen Electric 
Logo Shindengen Electric Logo 
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MR1721 datasheet
MR1721 pdf, equivalent, schematic
2-1 Basic Operation
Partial resonance power supplies are an
effective means of increasing efficiency
and reducing noise with a simple circuit
configuration. Partial resonance operation
requires detection of the secondary zero
current (0A) point, and determination of
the ON timing for the main switching
device. The MR1000 Series incorporates a
zero current detection pin (Z/C, pin 1), the
negative edge of the voltage in the control
coil (wound with opposite polarity to that
of the primary coil) being detected in the
main transformer and the main switching
device switched ON to detect the 0A point
of the secondary current. In order to
switch the main switching device ON at
the VDS resonance trough during partial
www.DartaeSshoeneat4nUc.ecomoperation it is necessary to
delay the ON timing for the primary
inductance by 1/2 of the resonance period
of the resonance condenser after the
secondary current reaches 0A, and simple
adjustment of the time constant of the
resistor and condenser connected to the IC
zero current detect pin (Z/C, pin 1) allows
the main switching device to be switched
ON at the VDS resonance trough.
[Secondary rectifying diode current]
[Control coil voltage]
Fig.1 ON Trigger Operation Sequence
2-2 Standby Functions
The MR1000 Series supports a
function to reduce power consumption
during standby by switching from the
normal operation mode to the burst
mode using an external signal. The
voltage at pin (1) is clamped to a
maximum of 2.9V (typ.) with a
microcomputer standby signal to
switch to the burst mode. Drain
current is then limited to IDP (burst) =
425mA (typ.), and intermittent
operation begins in which control of
the ON width is switched from linear
control of the voltage at the F/B pin
(pin (2)) to hysteresis operation in
which oscillation begins at VF/B >
1.8V and is halted at VF/B < 0.8V.
Drain pin
F/B pin
Z/C pin
GND pin
Standby signal
(external signal)
Output voltage
error detection
feedback signal
Fig.2 Standby Mode Selector Circuit
Password Vol.02-05-e MR1000 Series
All Rights Reserved Copyright (C) SHINDENGEN ELECTRIC MANUFACTURING CO., LTD. 2002

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