3.5 Output Voltage Control (normal operation)
The MR2000 Series controls output voltage with the ON
range proportional to the voltage at the F/B pin.
When the voltage at the F/B pin is 1.5V the ON range is
0µs, and is controlled in a linear manner so that when the
voltage is 4.5V the ON range is 25µs. A current of
200µA=IF/B (typical) flows at the F/B pin, and the
impedance of the photocoupler transistor connected
externally between the F/B pin and GND is varied with the
control signal from the secondary output detection circuit,
thus controlling the ON range of the main switching device
to produce a constant voltage.
The maximum ON range is adjusted by setting the
maximum value for the voltage at the F/B pin using a
resistor connected externally between the F/B pin and GND.
5Vref
200μA
F/B pin
Droop
resistor
2
Output voltage controlled
by varying impedance of
photocoupler.
Output voltage
error detection
feedback signal
ON range t
on
［μs�½
25
0
1.5
4.5
Feedback voltage
V
F/B
［V�½
Fig.3.8 Output Voltage Control
3.6 Soft Drive Circuit (patent applied for)
The MR2000 Series supplies the main switching device
gate drive voltage from two separate drive circuits.
A voltage exceeding the threshold value for the main
switching device is supplied from the first drive circuit at the
leading edge of the drive voltage waveform to switch on the
main switching device with the optimum timing.
The drive voltage is then supplied gradually by the second
drive circuit (see Fig.3.9).
Supply of drive voltage in this manner reduces drive losses,
as well as reducing noise due to gate charge current and
discharge current when the resonating condenser is
switched on.
Gate voltage supply
matched to collector
current.
【V
GE
】
Gate charge remains
unchanged even when
collector current is small.
Gate charge spikes
reduced.
【I
G
】
Reactive charge
reduced under
light load.
Large resonating
condenser discharge
current.
Damping of resonating
condenser discharge
current.
【I
C
】
【Conventional
drive circuit】
【MR2000
drive circuit】
Fig.3.9 Comparison of Drive Circuits
Shindengen Electric MFG.CO.,LTD
- 9 -
SHINDENGEN [ SHINDENGEN ELECTRIC MFG.CO.LTD ]
