Electronic – Current multiplier/divider for current measurement

currentcurrent measurement

You can change a current mirror into a multiplier/divider by adding transistors on either side. Then the number of transistors defines the current ratio. The transistors have to be integrated on the same chip to have a good precision (good matching), and besides, nobody wants to place 100 discrete transistors on his PCB for this.

Are there ICs for this, like a \$\times\$10 or \$\times\$100 multiplier (or \$\div\$10/\$\div\$100 divider, you should be able to use them for both)?

Best Answer

Zetex (now Diodes, stupid name) has a nice little IC which has been mentioned on this site a few times. The ZXCT1009 is a high side current sensor which works as a current divider, though to some extent (low currents) you'll also be able to use it as a multiplier.

enter image description here

The transfer function is

\$ I_{OUT} = \dfrac{R_{SENSE}}{100 \Omega} \cdot I_{SENSE} \$

so with a 1\$\Omega\$ sense resistor you get a \$\div\$100 divider; a 1k\$\Omega\$ resistor will multiply by 10. The output current is limited, but you can use the schematic to roll your own multiplier for higher currents:

enter image description here

Don't make the sense resistor too small; below 10mV voltage drop accuracy decreases fast.

edit (re your comment)
For high side current measurement I think this is an excellent IC. Choose a 100m\$\Omega\$ resistor for \$R_{SENSE}\$ and a 1k\$\Omega\$ for \$R_{OUT}\$ and you'll have a nice 1V/A output.

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