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1-3. PWA POWER CIRCUIT DESCRIPTION
1. Outline
This is the main power circuit, and is comprised of the follow-
ing blocks.
Switching power control IC (IC501)
Analog 13 V (A) output system (L5003, Q5001)
Analog -7.5 V (A) output system (L5005, Q5005, IC502)
Analog 3.5 V (A) output system (IC503)
Digital 3.25 V (D) output system (L5001)
Digital 1.20 V (D) output system (L5002)
Backlight output system (L5006, Q5007)
Boost power (L5301)
2. Switching Power Controller (IC501)
This is the basic circuit which is necessary for controlling the
power supply for a PWM-type switching regulator, and is pro-
vided with eight built-in channels.
PWM/PFM switching step-up circuit …… 1 (ch_1)
PWM drive step-up/step-down circuit …… 1 (ch_2)
PWM drive step-up and step-down circuit …… total 4 (ch_3
and ch_5~ch_7)
PWM drive inverter circuit …… 1 (ch_4)
Variable regulator …… 1 (ch_8)
Only ch_1 (starting IC, lens drive, 8-bit microprocessor and
ch_3 source), ch_2 (digital 3.25 V), ch_3 (digital 1.20 V), ch_4
(analog -7.5 V), ch_5 (analog 13 V), ch_6 (not used), ch_7
(backlight) and ch_8 (not used) are used. Feedback from 3.8
V (ch_1), 3.25 V (ch_2), 1.20 V (ch_3), -7.5 V (ch_4) and 13.0
V (ch_5) power supply outputs are received, and the PWM
duty is varied so that each one is maintained at the correct
voltage setting level.
Feedback for the backlight power (ch_7) is provided so that
regular current can be controlled to be current (approximately
20 mA) that was setting.
PWM/PFM switching can be carried out for ch_1, so that PFM
operation is enabled when the DSC is stopped (when the
power is off) which provides greater efficiency at times of low
loads (only the 8-bit microprocessor is driven).
2-1. Damage Prevention Circuit
When a short-circuit is generated for a constant period of time,
the capacitor that is connected to pin (1) of IC501 turns all
output off. It is also equipped with an overheating protection
circuit, so that when the element temperature becomes higher
than a certain temperature, all output is turned off in the same
way as for a short-circuit. To reset output, remove the cause
of the problem and then resend a control signal.
3. ch_1 Output System
3.6 V is output. Feedback for the 3.8 V output is provided to
the switching controller (Pin (36) of IC501) so that PWM con-
trol can be carried out. Also, it is the source for 3.5 V (A).
While DSC is stopped, control switches to PFM control.
4. ch_2 Output System
3.25 V (D) is output. Feedback for the 3.25 V (D) output is
provided to the switching controller (Pin (45) of IC501) so that
PWM control can be carried out.
5. ch_3 Output System
1.20 V (D) is output. Feedback for the 1.20 V (D) output is
provided to the swiching controller (Pin (44) of IC501) so that
PWM control can be carried out.
6. ch_4 Output System
-7.5 V is output. Feedback for the inverter circuit output is
provided to the switching power controller (Pin (38) of IC501)
so that PWM control can be carried out. This output is high
precision by IC503, and get to -7.5 V.
7. ch_5 Output System
13.0 V (A) is output. Feedback for the 13.0 V (A) is provided
to the switching power controller (Pin (39) of IC501) so that
PWM control can be carried out.
8. ch_7 Output System
Regular current is being transmitted to LED for backlight. Step-
down in the voltage from the LED are feedback to the switch-
ing power controller (Pin (42) of IC501) so that PWM control
can be carried out.
The control signal (LCD PWM) from the 8-bit system can be
used to adjust the backlight illumination.
