CIRCUIT OPERATIONS
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KX-FT21LA
Using a different winding ratio results in the voltage function given by the formula in figure (c).
As you can see, it is possible to keep VO constant by changing the ratio of TON and TOFF in response to variations
in input voltage.
T
OFF
T
ON
t
I
IN
0
T
OFF
T
ON
t
I
IN
0
(a) An input current I
IN
waveform when output current is low
(b) An input current I
IN
waveform when output current is high
Response to Variations in Output Current
In this case, V
O is kept constant by controlling only TON without changing the ratio between TON and TOFF in response to
variations in output current. Figure B (a) and (b) shows how T
ON varies in response to variations in output current.
The input current must be increased as output current increases, making T
ON longer. The value obtained by dividing the
surface area of the sawtooth waves in this figure by the time interval gives the average input current.
Principle of Constant Voltage Operation Given Variations
in the Output Current Under the RCC Method
<Figure B>
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