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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 3855
Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 3855
Keywords: current monitoring, current mirror, negative supply, op amps,MOSFETs
APPLICATION NOTE 3855
Precision Circuit Monitors Negative Supply Current
Jun 29, 2006
Abstract: This current-sensing circuit monitors a negative power supply and provides a positive output
voltage proportional to the load current.
Supply-current monitoring is a necessary feature in high-reliability systems where excessive current can
cause damage or compromise safety. Such systems avoid overload faults by monitoring their power
supply and shutting it down before a fault occurs. Most current-monitoring ICs, however, are designed for
positive-voltage supplies. For negative supplies, the circuit of Figure 1 monitors load current and
provides a proportional output voltage.
Figure 1. This current-sensing circuit monitors a negative power supply and provides a positive output
voltage proportional to the load current.
Voltages at the inverting and noninverting terminals of the op amp (IC1A) are forced to be equal by an
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