M62211P Просмотр технического описания (PDF) - MITSUBISHI ELECTRIC
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M62211P Datasheet PDF : 9 Pages
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MITSUBISHI SEMICONDUCTORS <Standard-Linear>
M62211P/FP
GENERAL PURPOSE MULTI FUNCTION DC-DC CONVERTER
1. Explanation of Back Light Control Circuit
VCC
Cl
Cosc
IN1
IN2
OSC &
sync ckt
OP Amp1
Std. voltage
1.25V
OP Amp2
UVLO
VTH :2.3V
R
SQ
DC/AC
D1
Co
FL
Tube
R1
R3
D2
VR1
R2
R4
CDELAY CFL
RFL
Cf2
Cf1
RDTC CDTC
Rl1
Rl2
Fig.1 An Application of the Back Light Control Circuit
1-1. Priority Control Operation
As far as OPAmp1 and OPAmp2 are concerned, there is no problem when either IN1 or IN2 is
used to control current, since the setting up to lower the output voltage of the DC-DC converter is
prioritized. (The above figure uses IN1 to control current.)
1) When starting, the output voltage "Vo" is determined by the feedback to IN2 via R1 and
R2 and the following equation :
Vo=VREF * (R1 + R2)/R2 (VREF =1.25Vtyp) (Area of the Timing Chart 1)
2) Next, this output voltage "Vo" is used to discharge the FL tube by the inverter and causes
the tube current to flow. The tube current is filtered and smoothed by RFL, D2, and CFL so
that the DC voltage (VCFL) corresponding to the tube current is generated at CFL.
The voltage of VCFL is divided by R3, VR1, and R4, and feedback to IN1, it can control tube
current. (Area of the Timing Chart 2)
3) Here, CDELAY is inserted between R3 and VR1 + R4 in order to regulate the timing to switch
from the voltage control to the current control. (Area of the Timing Chart 3)
4) When in the current control state, it is possible to adjust brightness by changing the
amount of feedback of the tube current using VR1. (Area of the Timing Chart 4)
5) If the feedback used for controlling current is lost due to irregularities in the FL tube. etc..
the control returns to the voltage control mode. (Area of the Timing Chart 5)
(4/9)
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