Daewoo DTA-14C4TFF Service Manual page 31

C1
(STR -F6653
internal capacitor)
Pin 1
(OCP / FB)
I
D
(M OSFET drain current)
V
D S
(M OSFET drain - source voltage)
M O S F E T switching ON / OFF
- 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
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 to the gradient regulated by the constant dis-
charging 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.
6.5 V
3.7 V
0.73 V
0V
OFF
ON
Waveforms during oscillating operation
= 0.73V, the STR-F6653 internal comparator 1 starts operating.
TH1
1
2
ON OFF
9
APPENDIX
FUNCTIONAL DESCRIPTION
3
4
ON
OFF