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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4501
Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 4501
Keywords: charge-pump voltage doublers, current-sense amplifiers, n-channel MOSFETs, inrush current
APPLICATION NOTE 4501
Simple Current Limiter Is Programmable
Nov 05, 2010
Abstract: This circuit lets you program a current limit without using microcontrollers or data converters. It
consists of a charge-pump voltage doubler (U1), a current-sense amplifier (U2), and two n-channel
MOSFETs. The sense-resistor value determines the maximum current limit.
A similar version of this article appeared in the May 18, 2009 issue of EE Times magazine.
Available integrated circuits can let you program a current limit, but they generally involve
microcontrollers or data converters (or both). As an alternative, the Figure 1 circuit lets you program a
current limit without the intervention of microcontrollers or data converters. It consists of two miniature
SOT-5 devices and a few external components. The sense-resistor value determines the maximum
current limit.
Figure 1. This circuit limits the R
LOAD
current to a value determined mainly by R1.
The circuit consists of a charge-pump voltage doubler (U1, MAX1682), a current-sense amplifier (U2,
MAX4376), and two n-channel MOSFETs. U1 doubles the supply voltage to provide gate drive for Q2,
and U2 amplifies the voltage across the sense resistor (R
SENSE
) with a gain of 20. This U2 output drives
the Q1 gate via the R2/R3 divider, which modulates the current through R1, which in turn sets the Q1
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