參數(shù)資料
型號(hào)： R1234D181A
廠商： Ricoh Co., Ltd.
英文描述： PWM/VFM Step-Down DC/DC CONVERTER with Synchronous Rectifier
中文描述： 脈寬調(diào)制/ VFM的降壓型DC / DC同步整流變換器
文件頁數(shù)： 12/26頁
文件大?。?/td> 876K
代理商： R1234D181A
R1234D
OPERATION of step-down DC/DC converter and Output Current
12
The step-down DC/DC converter charges energy in the inductor when L
X
transistor is ON, and discharges the
energy from the inductor when L
X
transistor is OFF and controls with less energy loss, so that a lower output
voltage than the input voltage is obtained. The operation will be explained with reference to the following
diagrams:
Step 1: P-channel Tr. turns on and current IL (
=
i1) flows, and energy is charged into CL. At this moment, IL
increases from Ilmin (
=
0) to reach ILmax in proportion to the on-time period (ton) of P-channel Tr.
Step 2: When P-channel Tr. turns off, Synchronous rectifier N-channel Tr. turns on in order that L maintains IL
at ILmax, and current IL (
=
i2) flows.
Step 3: IL (
=
i2) decreases gradually and reaches IL
=
ILmin
=
0 after a time period of topen, and N-channel Tr.
Turns off. Provided that in the continuous mode, next cycle starts before IL becomes to 0 because toff
time is not enough. In this case, IL value increases from this Ilmin (>0).
In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton),
with the oscillator frequency (fosc) being maintained constant.
Discontinuous Conduction Mode and Continuous Conduction Mode
Pch Tr
L
Nch Tr
V
IN
i1
V
OUT
CL
i2
GND
T
=
1/fosc
ton
toff
topen
ILmin
ILmax
IL
The maximum value (ILmax) and the minimum value (ILmin) of the current flowing through the inductor are the
same as those when P-channel Tr. turns on and off.
The difference between ILmax and ILmin, which is represented by
I;
I
=
ILmax
ILmin
=
V
OUT
×
topen/L
=
(V
IN
V
OUT
)
×
ton/L ........................................................Equation 1
Where, t
=
1/fosc
=
ton
+
toff
duty (%)
=
ton/t
×
100
=
ton
×
fosc
×
100
topen
<
=
toff
In Equation 1, V
OUT
×
topen/L and (V
IN
V
OUT
)
×
ton/L are respectively shown the change of the current at ON,
and the change of the current at OFF.
When the output current (I
OUT
) is relatively small, topen < toff as illustrated in the above diagram. In this case,
the energy is charged in the inductor during the time period of ton and is discharged in its entirely during the time
period of toff, therefore ILmin becomes to zero (ILmin
=
0). When I
OUT
is gradually increased, eventually, topen
becomes to toff (topen
=
toff), and when I
OUT
is further increased, ILmin becomes larger than zero (ILmin>0). The
former mode is referred to as the discontinuous mode and the latter mode is referred to as continuous mode.
相關(guān)PDF資料
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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