M51995 Mitsubishi, M51995 Datasheet - Page 18

• Manufacturer Part Number: M51995
• Description: SWITCHING REGULATOR CONTROL
• Manufacturer: Mitsubishi

Fig.20 shows how to connect the ON/OFF terminal.The
switching operation will stop by swich-off and operate by switch-
on.
Transistor or photo transistor can be replaced by this switch,of
course.No resistor of 30 to 100k is connected and ON/OFF
terminal is directly connected to GND,when it is not necessary
to use the ON/OFF operation.
Fig.21 shows the Icc versus Vcc characteristics in OFF state
and Vcc will be kept at not so high or low but at the adequate
voltage,when R1 shown in Fig.1 and 2 is selected properly.
OPERATE STOP AT Q4 ON
I:3µA AT STOPPING
I:20µA AT OPERATING
0.4
1.2
1.6
0.8
0
0
30k~100k
Fig.20 Connecting of ON/OFF terminal
ON/OFF
Fig.19 ON/OFF circuit
5
Fig.21 Icc vs.Vcc in OFF state
SUPPLY VOLTAGE Vcc(V)
Vcc
10
2k
ON/OFF
15
M51995A
I
20
Q2
Q3
25
Q4
30
(
18
/ 27 )
OVP circuit(over voltage protection circuit)section
OVP circuit is basically positive feedback circuit constructed by
Q2,Q3 as shown in Fig.22.
Q2,Q3 turn on and the circuit operation of IC stops,when the
input signal is applied to OVP terminal.(threshold voltage ~
750mV)
The current value of I2 is about 150µA when the OVP does not
operates but it decreases to about 2µA when OVP operates.
It is necessary to input the sufficient larger current(800µA to
8mA)than I2 for triggering the OVP operation.
The reason to decrease I2 is that it is necessary that Icc at the
OVP rest supply voltage is small.
It is necessary that OVP state holds by circuit current from R1 in
the application example,so this IC has the characteristic of
small Icc at the OVP reset supply voltage(~stand-by current +
20µA)
On the other hand,the circuit current is large in the higher
supply voltage,so the supply voltage of this IC doesn't become
so high by the voltage drop across R1.
This characteristic is shown in Fig.23.
The OVP terminal input current in the voltage lower than the
OVP threshold voltage is based on I2 and the input current in
the voltage higher than the OVP threshold voltage is the sum of
the current flowing to the base of Q3 and the current flowing
from the collector of Q2 to the base.
For holding in the latch state,it is necessary that the OVP
terminal voltage is kept in the voltage higher than V
So if the capacitor is connected between the OVP terminal and
GND,even though Q2 turns on in a moment by the surge
voltage,etc,this latch action does not hold if the OVP terminal
voltage does not become higher than V
this capacitor.
For resetting OVP state,it is necessary to make the OVP
terminal voltage lower than the OVP L threshold voltage or
make Vcc lower than the OVP reset supply voltage.
As the OVP reset voltage is settled on the rather high voltage of
9.0V,SMPS can be reset in rather short time from the switch-off
of the AC power source if the smoothing capacitor is not so
large value.
SWITCHING REGULATOR CONTROL
M51995AP/FP
BE
of Q3 by charging
BE
of Q3.