M51995AP

Manufacturer Part NumberM51995AP
DescriptionSwitching regulator control
ManufacturerMITSUBISHI
M51995AP datasheet
 
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NO OPERATING
DURATION
2V
Fig.15 Waveform of CT terminal
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.
2.0
1.5
1.0
0.5
0
0
5
10
15
SUPPLY VOLTAGE Vcc(V)
Fig.16 Icc vs.Vcc in timer-off duration
of intermittent action circuit
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.
Voltage detector circuit(DET) section
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
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
8V
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.
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25
30
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.
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17
M51995AP/FP
SWITCHING REGULATOR CONTROL
500
3k
1S
6S
F/B
DET
5.4k
10.8k
10.8k
10S
1.2k
Fig.17 Equivalent circuit diagram of
voltage detector
~7.1V
3k
500
1S
6S
F/B
-
DET
OP
AMP
+
2.5V
Fig.18 Equivalent circuit diagram of
voltage detector
~7.1V