3.11 Malfunction Prevention Circuit (patent applied for)
On-trigger disabled during
this period.
0.2V
The use of current-critical operation in the MR2000
Series ensures that the main transformer does not
become saturated provided the droop setting is
optimized.
2.5μs
【VZ/C
】
】
Enlarged
view
On the other hand, at start-up, and in the case of a
load short, the output voltage is very much less than
the set voltage.
As the control coil voltage is proportional to the output
voltage it also reaches an extremely small value, and
the on-trigger timing may be incorrectly detected due
to the ringing voltage while the device is OFF and
switched on before the current-critical point.
【IC
【Secondary rectification diode】
【VZ/C
】
To counter this problem, the MR2000 Series
incorporates a circuit to prevent on-trigger malfunction
at start-up, and in the case of a load short. This function
disables the on-trigger for a period of 2.7μs (typical)
after the main switching device in the IC is switched
OFF (on-dead time). This prevents incorrect detection
due to the ringing voltage while the device is OFF.
【IC】
【Secondary rectification diode】
This design permits detection of the point at which the
transformer secondary current is 0A at start-up, and in
the case of a load short. The main switching device is
then switched on at this point, allowing abnormal
oscillation to be controlled.
【VCE
】
【VOUT
】
Fig.3.11 Comparison of Drive Circuits
Body diode
3.12 Over-current Protection Circuit
Collector pin
7
A current detection resistor is connected between the
Emitter/OCL pin and GND to detect current between
the emitter of the main switching device and the emitter
current detection pin.
Resonating
condenser
Emitter/OCL
pin
6
During stable operation the main switching device
current is limited by pulse-by-pulse operation with the
0.6V threshold value.
Current detection
resistor
The leading edge clamp function prevents
malfunctioning and thus prevents incorrect detection at
turn-on.
Fig.3.12 Current Detection Resistor
During standby, the 50mV threshold value is selected and the oscillation noise from the transformer due to burst oscillation is
reduced.
Shindengen Electric MFG.CO.,LTD
- 11 -
SHINDENGEN [ SHINDENGEN ELECTRIC MFG.CO.LTD ]
