When any of the controlling lines is in abnormality, the radio reception will be in malfunction. The
RDS signal received by radio head will be delivered to the dedicated IC SAA6588 for processing.
Chapter IV Operating Principle of Power Board
I. Block Diagram
This amplifier has two groups of power supply; one is of low voltage for decoding board and low
power ICS, the other is of higher voltage for power amplifying IC. But their design principles, we
only draw one functional block diagram of them:
II. Introduction of Circuit Principle
220V alternating current is loaded on D501-D504 integrated bridging rectification circuit through
power plug, fuse tube, voltage dependent resistor R501 and common mode rejection BC501 and
L501. Diode adopts IN4007 which ahs better PPR and higher withstand voltage value than IN4001.
Output 311V direct current after being bridging rectified is loaded on two transformers through
TC501 filtering and transmitted to DRAIN control pins of switch modules U501 and U502.
Service voltage of power on IC after being directly rectified and filtered is divided by resistors to
serve IC. Diode D508, capacitor C516 and resistor R516 form absorption circuit to provide
discharge circuit of reverse electromotive force for 1-4 coils of transformers. Pin FB controlling IC
is feedback control pin, so you should decide on/off time of pulse width according to current
intensity on it to ensure stability of output voltage.
There are 5 branch circuits coupled to sub-grade through transformer.
1. Voltage output from pin 11 and pin 13 of transformer T501 outputs a group of +28V voltage
for power amplifying IC after being rectified and filtered.
2. Voltage output from pin 16 of transformer T501 outputs a group of +12V voltage after being
rectified and filtered. +12V voltage is stabilized into a group of +5V voltage by IC LM7805.
3. Voltage output from pin 14 of transformer T501 o5V voltage and provide voltage for
one end of photo-electric coupler U502 after being rectified and filtered.
4. Voltage output from pin 12 of transformer T501 o3.3V voltage and provide a group of
stable voltage for CPU after being rectified and filtered.
5. Voltage output from pin 9 of transformer T501 outputs a group of 21V voltage for displaying
driving IC after being rectified and filtered. Clamp ZD501 of -21V provide heater voltage for
panel display screen. Grounding direct voltage of FL+ and FL- is about -16V.
Operating principles of two groups of switch power are the same, therefore we will only analyze
the group pro3.3V voltage for CPU here:
Feedback sampling of this group comes from 3.3V and supplies for photocupler HS817 through
D516 and R506. At the same time, it is divided through R508 and R509 for reference voltage pin R
of 2.5V comparator. When 3.3V becomes higher, pin KA of comparator is on; and the voltage is
transmitted to pin 4 of switch IC 5L0380R after photoelectric coupling through HS817 to reduce
on time of internal switch tube. And thus it reduces transformer coupling and decreases output of
3.3V voltage to achieve automatic adjustment and control, and vice verse.
It has to be noted that in this switching power reference voltage comparator IC of two groups of
switching power are different. For voltage of the group supplying power for amplifier is higher, it
adopts LM431 which has better performance and higher withstand voltage. And voltage of the