TK75018 Ver la hoja de datos (PDF) - Toko America Inc
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TK75018 Datasheet PDF : 8 Pages
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TK75018
TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)
OUTPUT VOLTAGE LOSS VS.
OSCILLATOR FREQUENCY
INVERTER CONFIGURATION
2.0 CIN = 2.2 µF TANTALUM
COUT = 33 µF TANTALUM
OUTPUT VOLTAGE LOSS VS.
OSCILLATOR FREQUENCY
INVERTER CONFIGURATION
2.0 CIN = 22 µF TANTALUM
COUT = 33 µF TANTALUM
1.0
0
1
IOUT =10 mA
1.0
Note 4 Test Circuit
0
10
100
1
fOSC (kHz)
IOUT =10 mA
Note 4 Test Circuit
10
100
fOSC (kHz)
OUTPUT VOLTAGE LOSS VS.
INPUT CAPACITOR
1.0
INVERTER CONFIGURATION
COUT = 33µF TANTALUM
0.8 fOSC = 25 kHz
IOUT = 10 mA
0.6
0.4
0.2
0
0
Note 4 Test Circuit
20 40 60 80 100
CIN (µF)
THEORY OF OPERATION
As in any switched capacitor converter, the means of
conveying energy from input to output is done by charging
a capacitor between two potentials and then switching one
end of the capacitor to a different potential. By some
means of rectification, the other end of the capacitor is then
forced to dump charge into another capacitor at the
converter output, thereby conveying energy.
In a simple example shown in Figure 1, a capacitor C1 has
one side tied to ground and another side charged by a
voltage source of potential V1. The non-grounded side of
C1 is then switched over to be connected to one side of a
capacitor C2, which is at potential V2 and referenced to
ground. V2 represents the output of the converter. The
initial charge on C1 is:
q1 = C1 x V1
When the switch changes over to the V2 side, C1 is
discharged from potential V1 to potential V2. After discharge
has occurred the charge on C1 is then:
q2 = C1 x V2
This means that the net transfer of charge which has
occurred is:
V1
fO
C1
V2
IL
C2
FIGURE 1: SWITCHED CAPACITOR CIRCUIT
If the potential V2 is sourcing a current IL, the charge will
have to be delivered at a rate:
ƒO = IL /∆q = IL / C1(V1 – V2)
Thus, the higher the frequency, the more current that can
be supported by the converter output.
All else being ideal, the effective losses in the converter in
the energy conveyance process is identical to that of a
circuit consisting of a resistor between the potentials V1
and V2, with the same load at the output side. This
equivalent resistor is simply:
REQUIV = (V1 – V2) / IL = 1 / (ƒO x C1)
∆q = q1 – q2 = C1 (V1 – V2)
May 1999 TOKO, Inc.
Page 5
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