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參數(shù)資料
| 型號： | R1280D002C-TR |
| 文件頁數(shù)： | 8/26頁 |
| 文件大小： | 344K |
| 代理商： | R1280D002C-TR |
Rev.1.10 - 8 -
I
Operation of Step-up DC/DC Converter and Output Current
Step-up DC/DC Converter makes higher output voltage than input voltage by releasing the energy accumulated
during on time of Lx Transistor on input voltage.
<Basic Circuit>
Inductor
Diode
C
L
Lx Tr
V
IN
V
OUT
I
OUT
ILxmax
ILxmin
Ton
Toff
T=1/fosc
Tf
IL
Discontinuous Mode
t
ILxmax
ILxmin
Ton
Toff
T=1/fosc
t
IL
Iconst
Continuous Mode
<Current through L>
GND
i1
i2
Step 1. Lx Tr. is on, then the current IL=i1 flows, and the energy is charged in L. In proportion to the on time of Lx Tr.
(Ton), IL=i1 increases from IL=ILxmin=0 and reaches ILxmax.
Step 2. When the Lx Tr. is off, L turns on Schottky Diode (SD), and IL=i2 flows to maintain IL=ILxmax.
Step 3. IL=i2 gradually decreases, and after Tf passes, IL=ILxmin=0 is true, then SD turns off. Note that in the case of
the continuous mode, before IL=ILxmin=0 is true, Toff passes, and the next cycle starts, then Lx Tr. turns on again.
In this case, ILxmin>0, therefore IL=ILxmin>0 is another starting point and ILx max increases.
With the PWM controller, switching times during the time unit are fixed. By controlling Ton, output voltage is
maintained.
I
Output Current and Selection of External Components
Output Current of Step-up Circuit and External Components
There are two modes, or discontinuous mode and continuous mode for the PWM step-up switching regulator
depending on the continuous characteristic of inductor current.
During on time of the transistor, when the voltage added on to the inductor is described as V
IN
, the current is V
IN
×
t/L.
Therefore, the electric power, P
ON
, which is supplied with input side, can be described as in next formula.
T
ON
ON
∫
V
IN
2
×
t/L dt
0
Formula 1
With the step-up circuit, electric power is supplied from power source also during off time. In this case, input current is
described as (V
OUT
-V
IN
)
×
t/L, therefore electric power, P
OFF
is described as in next formula.
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相關代理商/技術參數(shù) |
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