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10000_V_STANDARD

2015-03-19 13:16  
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10000_V_STANDARD
The heart of the voltage standard is the LT1027BCH voltage reference IC, IC2, manufactured by Linear Technology Corp. It sports a temperature coefficient of two parts per million per degree Celsius (2 PPM/℃), and it comes pretrimmed within ±0.05 percent. Provision for optional trim circuitry is included on the board; however, it requires an additional resistor-selection step. To eliminate sensitivity to input-voltage variations, the incoming supply is regulated at 15 Vdc. This is accomplished with a conventional LM340T15 voltage regulator, which powers both the reference IC and the output amplifier. The LT1050 amplifier doubles the 5-V output of the LT1027 to the desired 10 Vdc. It is chopper-stabilized, providing far lower drift than a conventional op amp. Noise filtering is provided by the 0.47-μF capacitor across the feedback resistor. Note that the LT1050 does not have the out-put drive of a bipolar device-thus, the slightly higher than normal feedback resistors. You should not try to use the voltage standard with loads below 10 kΩ. The 0.47-μF/49.9-Ω output network improves stability when cables and capacitive loads are driven.