M51996AP Datasheet, PDF (19/36 Pages) Mitsubishi Electric Semiconductor – SWITCHING REGULATOR CONTROL

M51996AP/AFP
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 figure 11. As well known from
figure 11 and figure 12, the output of OP AMP has the current-sink ability, when the DET terminal voltage is higher
than 2.5 V.
But it becomes high impedance state when lower than 2.5 V 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.
3k
500 Ω
≈ 7.1 V
1S
6S
F/B
DET
5.4 k
10.8 k 10.8 k
10 S
1.2 k
Figure 11 Voltage Detector Circuit Section (DET)
3k
500 Ω
≈ 7.1 V
1S
6S
F/B
OP ^−
AMP ₊
DET
2.5 V
Figure 12 Schematic Diagram of Voltage Detector Circuit Section (DET)
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
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