Service manual CP 385 / CP785
- 48 -
¬
When the MOSFET is ON, the STR-F6653 internal capacitor C1 is charged at the constant voltage
6.5V.
At the same time, the voltage at pin 1 (OCP / FB) increases with the same waveform as the MOSFET
drain current.
-
When the pin 1 voltage reaches the threshold voltage V
TH1
= 0.73V, the STR-F6653 internal
comparator 1 starts operating. The STR-F6653 internal oscillator is inverted and the MOSFET turns
OFF.
®
When the MOSFET turns OFF, charging of STR-F6653 internal capacitor C1 is released and C1
starts discharging by the STR-F6653 internal resistance R1. So, C1 voltage starts falling in accordance
with the gradient regulated by the constant discharging time of C1 and R1. So, this means that the fixed
time determined by C1 and R1 is the OFF-time of the MOSFET.
¯
When C1 voltage falls to around 3.7V, the STR-F6653 internal oscillator is reversed again and the
MOSFET turns ON. C1 is quickly charged to around 6.5V
The MOSFET continues to oscillate by repeating the above procedure.
* STR-F6653 protection circuits
•
overcurrent protection function (OCP)
Overcurrent protection is performed pulse by pulse detecting at STR-F6653 pin 1 (OCP) the peak of the
MOSFET drain current in every pulse.
•
latch circuit
This circuit sustains an output low from the STR-F6653 internal oscillator and stops operation of the
power supply when overvoltage protection (OVP) and thermal shutdown (TSD) circuit are under
operation
•
thermal shutdown circuit (TSD)
This circuit triggers the latch circuit when the frame temperature of STR-F6653 IC exceeds 140
°
C
•
overvoltage protection circuit (OVP)
This circuit triggers the latch circuit when the V
in
voltage exceeds 22V (typ.)
Summary of Contents for DTA-20 T1
Page 17: ...Service manual CP 385 CP785 16...
Page 21: ...Service manual CP 385 CP785 20...
Page 34: ...Service manual CP 385 CP785 33 5 Circuit description 5 1 Block diagram...
Page 39: ...Service manual CP 385 CP785 38 Chassis block diagram IF...
Page 43: ...Service manual CP 385 CP785 42 Sound signal flow diagram...
Page 70: ...69 Service Manual cp 385 cp 785 7 Exploded View 7 1 DTA 20T1...
Page 73: ...72 7 4 DTA 20T8 Service Manual cp 385 cp 785...
Page 74: ...73 7 5 DTA 21T1 Service Manual cp 385 cp 785...
Page 76: ...75 7 7 DTA 21T5 Service Manual cp 385 cp 785...
Page 77: ...76 7 8 DTA 21T9 Service Manual cp 385 cp 785...
Page 79: ...78 Service Manual cp 385 cp 785 7 10 DTE 25G6...
Page 80: ...79 Service Manual cp 385 cp 785 7 11 DTE 25G7...
Page 82: ...81 7 13 DTE 28G6 Service Manual cp 385 cp 785...
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