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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4568
Maxim > Design Support > Technical Documents > Application Notes > Circuit Protection > APP 4568
Maxim > Design Support > Technical Documents > Application Notes > Microprocessor Supervisor Circuits > APP 4568
Keywords: bipolar dc-voltage detection, high-impedance inputs, galvanic isolation
APPLICATION NOTE 4568
Bipolar DC-Voltage Detector Offers Sensitivity and
Precision
Jan 26, 2011
Abstract: Comprised of two precision op amps (MAX4236), a voltage reference (MAX6143), a NAND
gate, and associated components, this DC-voltage detector circuit asserts a digital output signal when
the input is within a ±100mV window, centered at 0V.
A similar version of this article appeared in the June 1, 2007 issue of Power Electronics Technology
magazine.
An important function in industrial and scientific applications is detecting the presence (or absence) of DC
voltages in safety interlocks, automatic sequencers, etc. To detect the absence of large bipolar DC
levels, the detector must assert a signal when its input is within a stable and precisely defined window
around zero volts. The window width should be twice the maximum tolerable error voltage, and centered
at zero volts.
The detection circuit must have a high-impedance input to avoid affecting the system into which it is
inserted. It must also tolerate an input level equal to the the maximum voltage it supervises plus the
amplitude of any transient that might appear. One circuit that meets those requirements (Figure 1)
produces a digital output signal when the input voltage is within a ±100mV window.
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