M62211FP Ver la hoja de datos (PDF) - Renesas Electronics
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M62211FP Datasheet PDF : 12 Pages
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M62211P/FP
Explanation of Back Light Control Circuit
VCC
C1 +
COSC
IN1
IN2
OSC &
sync ckt
OP Amp1
Std voltage
1.25 V
OP Amp2
UVLO
VTH = 2.3 V
R
SQ
D1
DC/AC
C0 +
R1
FL
Tube
VR1
R2 R4
R3 D2
+
RFL
CDELAY CFL
Cf2 Cf1
RDTC
+
CDTC
RI1
RI2
Figure 1 An Application of the Back Light Control Circuit
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 = 1.25 V typ) (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)
REJ03D0842-0201 Rev.2.01 Nov 14, 2007
Page 5 of 11
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