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4~20mA current transmitter circuit with digital pressure sig

2016-04-11 17:57  
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4~20mA current transmitter circuit with digital pressure signal disposal device MAX1459
PGA's output voltage is sentto spare amplifier in chip, then we can get 4~20mA output current by external power amplifier circuit. In long-distance transmission current, the current signal's precision is not influenced by the resistance of cable. PN4391 is a 40V, 150mANFET. MAX875's voltage temperature coefficient is 7×10-6/℃. The 3mA constant current source iscomposedof PN4391 and MAX875, and it provides stable work current to MAX145, then it uses MAX1459 to take temperature compensation and gain compensation. MAX1459's output voltage is converted into 4 ~ 20mA current signal through backup amplifier and power amplifier, and its loop power range is + 12 ~ 40V. VT uses 2N2222 power tube, and its main parameters are: UCEO = 60 V, ICM = 0.8 A. The initial voltage of measuring resistance is set by resistors R1 ~ R 4, and the signal voltage of RSENSE is controlled by MAX1459.