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Basic Application Circuits
Application Information
VOLTAGE DOUBLING INVERTER
The main application of the LM2682 is to generate a nega-
tive voltage that is twice the positive input voltage. This
circuit requires only three external capacitors and is con-
nected as shown in Figure 1. It is important to keep in mind
that the efficiency of the circuit is determined by the output
resistance. A derivation of the output resistance is shown
below:
R
OUT = 2(RSW1+RSW2+ESRC1+RSW3+RSW4+ESRC2)+
2(R
SW1+RSW2+ESRC1+RSW3+RSW4+ESRC2)+
1/(f
OSCxC1) + 1/(fOSCxC2) + ESRC3
Using the assumption that all four switches have the same
ON resistance our equation becomes:
R
OUT = 16RSW + 4ESRC1 + 4ESRC2 + ESRC3 +
1/(f
OSCxC1) + 1/(fOSCxC2)
Output resistance is typically 90
with an input voltage of
+5V, an operating temperature of 25C, and using low ESR
3.3 F capacitors. This equation shows the importance of
capacitor selection. Large value, low ESR capacitors will
reduce the output resistance significantly but will also require
a larger overall circuit. Smaller capacitors will take up less
space but can lower efficiency greatly if the ESR is large.
Also to be considered is that C1 must be rated at 6 VDC or
greater while C2 and C3 must be rated at 12 VDC or greater.
10099703
FIGURE 1. Doubling Voltage Inverter
10099704
FIGURE 2. +5V to 5V Regulated Voltage Converter
LM2682
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相关代理商/技术参数
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