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App note: Add high voltage capability to current sense monitors

Posted on Saturday, April 14th, 2012 in app notes by DP

Here is an app note from Maxim describing how to add high voltage capability up to 300V for the MAX47X (which have been replaced by MAX407X)  bidirectional current sense monitors. Since the MAX47X draw low current, a simple floating power supply can be used to power the device even at 300V.

The circuit of Figure 1 shows a simple way to add high voltage capability to the basic MAX471/2. Low supply current of the current monitor (100µA) allows a very simple floating power supply formed by avalanche diode D1, C1, C2, and the NPN current source Q1 and Q2. The voltage compliance of the current source provides the high voltage capability. With the part shown, Motorola MPSA42 (Q1), 300V is the maximum recommended, giving an absolute maximum input voltage rating for the whole circuit of 305.1V. Use of a 33V avalanche diode for D1 pushes this to 333V.

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