Page 1
Circuit Description
NEC-FA150ATUA
1. Audio circuit (Circuit diagrams Main PWB) KT
1.1 Audio input
The audio signal input received from the audio input terminal (J301) is applied to the amplifier I314 of 4 (L-CH)
and 9 (R-CH) through the low-pass filter consisting of R374, R376, R378, R379, C464 and C465.
In this amplifier, controls of Volume, and mute are conducted. The audio signal controlled at the pin 6 deter-
mines the attenuation of output of the amplifiers. Since then, the signal is output to the jack P307.
1.2 Audio output
The audio signal is output from the jack output terminal (P307) of the jack board to the internal speaker system.
2. Power supply (Circuit daigrams MAIN PWB)
1. Line filter consists of C801, T801, C803, C804. It eliminates high frequency interference to meet EMIs
requirement.
2. Rec & Filter
Bridge diode D801 converts AC source into pulsed DC. This pulsed DC is smoothed and filtered by C805.
R802 is an NTC ( negative thermal coefficient ) resistor, used to reduce inrush current to be within safe range.
3. Power transformer :
T802 converts energy from power source C805 to secondary side to ge12V and +5V.
4. Output :
When driver Q803 is driven on and off by I801, pin 6 and pin 9 of T802 induce a square wave. This square
wave is rectified by D809, D810, then filtered by C817, C822 to ge12V and +5V respectively.
5. Driver : Q803
If the electrical potential of gate is larger than source by about 10 volts, Q803 turns on.
6. FB :
Negative feedback CKT consists of photo coupler I802 and adjustable regulator I803. It can maintain output
vo5V and +12V at a stable level.
7. PWM :
7.1
7.1
7.1
7.1
7.1
Start
Start
Start
Start
Start
: When power is turned on, Q801 conducts due to bias from C805 and R803. Q801 supplies a 17 volt
: When power is turned on, Q801 conducts due to bias from C805 and R803. Q801 supplies a 17 volt
: When power is turned on, Q801 conducts due to bias from C805 and R803. Q801 supplies a 17 volt
: When power is turned on, Q801 conducts due to bias from C805 and R803. Q801 supplies a 17 volt
: When power is turned on, Q801 conducts due to bias from C805 and R803. Q801 supplies a 17 volt
and a starting current about 0.3mA to pin 7 of I801. I801 starts to oscillate (R816, C813) and outputs a pulse
and a starting current about 0.3mA to pin 7 of I801. I801 starts to oscillate (R816, C813) and outputs a pulse
and a starting current about 0.3mA to pin 7 of I801. I801 starts to oscillate (R816, C813) and outputs a pulse
and a starting current about 0.3mA to pin 7 of I801. I801 starts to oscillate (R816, C813) and outputs a pulse
and a starting current about 0.3mA to pin 7 of I801. I801 starts to oscillate (R816, C813) and outputs a pulse
train through pin 6 to drive Q803.
train through pin 6 to drive Q803.
train through pin 6 to drive Q803.
train through pin 6 to drive Q803.
train through pin 6 to drive Q803.
7.2
7.2
7.2
7.2
7.2
OPP
OPP
OPP
OPP
OPP
: When Q803 turns on, C805 supplies a linearly increasing triangle current through the primary induc-
: When Q803 turns on, C805 supplies a linearly increasing triangle current through the primary induc-
: When Q803 turns on, C805 supplies a linearly increasing triangle current through the primary induc-
: When Q803 turns on, C805 supplies a linearly increasing triangle current through the primary induc-
: When Q803 turns on, C805 supplies a linearly increasing triangle current through the primary induc-
tance of T802 to the driver Q803, once the peak value of this current multiplied by R81
tance of T802 to the driver Q803, once the peak value of this current multiplied by R81
tance of T802 to the driver Q803, once the peak value of this current multiplied by R81
tance of T802 to the driver Q803, once the peak value of this current multiplied by R81
tance of T802 to the driver Q803, once the peak value of this current multiplied by R81
1 exceeds1 volt, pulse
1 exceeds1 volt, pulse
1 exceeds1 volt, pulse
1 exceeds1 volt, pulse
1 exceeds1 volt, pulse
train will be shut down immediately to protect Q803, T802 from being burned out.
train will be shut down immediately to protect Q803, T802 from being burned out.
train will be shut down immediately to protect Q803, T802 from being burned out.
train will be shut down immediately to protect Q803, T802 from being burned out.
train will be shut down immediately to protect Q803, T802 from being burned out.
7.3
7.3
7.3
7.3
7.3
Regulation
Regulation
Regulation
Regulation
Regulation
: If output v5V goes up, the R terminal of I803 gets more bias, accordingly photo transis-
: If output v5V goes up, the R terminal of I803 gets more bias, accordingly photo transis-
: If output v5V goes up, the R terminal of I803 gets more bias, accordingly photo transis-
: If output v5V goes up, the R terminal of I803 gets more bias, accordingly photo transis-
: If output v5V goes up, the R terminal of I803 gets more bias, accordingly photo transis-
tor and photo diode flows more current. The voltage of pin 2 goes up too, making the pulse width of pin 6 to
tor and photo diode flows more current. The voltage of pin 2 goes up too, making the pulse width of pin 6 to
tor and photo diode flows more current. The voltage of pin 2 goes up too, making the pulse width of pin 6 to
tor and photo diode flows more current. The voltage of pin 2 goes up too, making the pulse width of pin 6 to
tor and photo diode flows more current. The voltage of pin 2 goes up too, making the pulse width of pin 6 to
become narrower. So the output v5V will be pulled down to a stable value.
become narrower. So the output v5V will be pulled down to a stable value.
become narrower. So the output v5V will be pulled down to a stable value.
become narrower. So the output v5V will be pulled down to a stable value.
become narrower. So the output v5V will be pulled down to a stable value.