A circuit diagram of the digital pressure signal conditioner MAX1459 4 ~ 20mA current transmitter

4 ~ 20mA current transmitter circuit from the MAX1459 configured as shown in FIG. The PGA output voltage supplied to the spare amplifier chip, and then through an external powe

r amplifier can obtain 4 ~ 20mA current output, the current long-distance transmission, the accuracy of the current signal is not affected by cable resistance. PN4391 to 40V, 150mA N-channel FET (NFET). MAX875 low-power, low drift 5V bandgap reference voltage source, the voltage temperature coefficient of 7 10-6/. Constituted by the PN4391 and MAX875 3mA of constant current source, to provide a stable operating current MAX1459, MAX1459 re-use temperature compensation and gain compensation (not shown pressure sensor). MAX1459 output voltage sequentially through spare amplifier, power amplifier into a current signal 4 ~ 20mA, allowing loop supply range is + 12 ~ 40V. VT use 2N2222 type power tube, its main parameters: UCEO 60V, ICM 0.8A. In UIN +, UIN- a parallel between the regulator, overvoltage protection can play a role. The initial voltage across the sense resistor RSENSE set by resistors R1 ~ R4, the signal voltage across RSENSE is controlled by the MAX1459. When RSENSE 50, the available standard voltage 0.2 ~ 1.0V calibrated. C1 ~ C3 as a decoupling capacitor, C4, C5 for the filter capacitor, C6 frequency compensation capacitor. R5, R6, respectively collector resistance and base resistance.

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