M51995 Mitsubishi, M51995 Datasheet - Page 17

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

Fig.16 shows the Icc versus Vcc in this timer-off duration.
In this duration the power is not supplied to IC from the third
winding of transformer but through from the resistor R1
connected toVcc line.
If the R1 shown in Fig.1 and 2 is selected adequate value,Vcc
terminal voltage will be kept at not so high or low but adequate
value,as the Icc versus Vcc characteristics has such the one
shown in Fig.16.
To ground the CT terminal is recommended,when the
intermittent mode is not used.
In this case the oscillated frequency will become low but the IC
will neither stop the oscillation nor change to the intermittent
action mode,when the current limit function becomes to operate
and the VF terminal voltage becomes low.
The DET terminal can be used to control the output voltage
which is determined by the winding ratio of fly back transformer
in fly-back system or in case of common ground circuit
Voltage detector circuit(DET) section
1.5
0.5
1.0
2.0
0
0
Fig.15 Waveform of CT terminal
Fig.16 Icc vs.Vcc in timer-off duration
5
NO OPERATING
DURATION
SUPPLY VOLTAGE Vcc(V)
of intermittent action circuit
10
15
2V
20
8V
25
30
(
17
/ 27 )
ON-OFF circuit section
Fig.19 shows the circuit diagram of ON-OFF circuit.The current
flown into the ON-OFF terminal makes the Q4 "on" and the
switching operation stop.On the other hand.the switching
operation will recover as no current flown into ON/OFF terminal
makes Q4 "off" As the constant current source connected to Q4
base terminal has such the hysteresis characteristics of 20µA at
operation and 3µA at stopping.So the unstable operation is not
appeared even if the ON/OFF terminal voltage signal varies
slowly.
of primary and secondary in feed forward system.
The circuit diagram is quite similar to that of shunt regulator
type 431 as shown in Fig.17.As well known from Fig.17 and
Fig.18,the output of OP AMP has the current-sink ability,when
the DET terminal voltage is higher than 2.5V but it becomes
high impedance state when lower than 2.5V DET terminal and
F/B terminal have inverting phase characteristics each other,so
it is recommended to connect the resistor and capacitor in
series between them for phase compensation.It is very
important,one can not connect by resistor directly as there is the
voltage difference between them and the capacitor has the DC
stopper function.
Fig.17 Equivalent circuit diagram of
1S
SWITCHING REGULATOR CONTROL
Fig.18 Equivalent circuit diagram of
1S
3k
3k
voltage detector
6S
voltage detector
500
6S
500
OP
AMP
10S
F/B
M51995AP/FP
F/B
+
-
1.2k
10.8k
~7.1V
2.5V
10.8k
5.4k
DET
DET
~7.1V