DC millivolt sources are often used for thermocouple simulations, DMM, ADC and analog circuit calibrations and fault findings, etc. Most of the DC millivolt circuits are based on expensive (and sometimes hard to find) operation amplifier like OP7, LT1077, etc. In this article we introduce low cost DC millivolt source based on commonly available LM308 precision operational amplifier, ICL8069 low voltage reference and 78L05 voltage regulator ICs. This millivolt source is design to obtain 200mV - 700mV DC output with 100Ω impedance. At the time of writing we spend Rs.800.00 (LKR) to complete this project.

MINI-SRC-500MV-S.JPG
Finished version of DC millivolt source with 500mV output.

The most expensive component in this project is Bourns 10K linear multi-turn potentiometer. We use Bourns potentiometer because of its reliability and durability, but any 10K linear multi-turn potentiometers can be used with this circuit. To get more accurate results use metal film resistors with ≤ 1% tolerance and Aluminum / Tantalum electrolytic capacitors for both C1 and C2.

The output impedance of this millivolt source is set to 100Ω to work with most of the high impedance test instruments.

This unit need external DC power source and we recommend 9V to 25V (100mA) single rail power supply or 9V battery to drive this circuit. This DC millivolt source is easy to build and PCB is the most recommended way to construct this project.

Project Related Downloads


Schematic and PCB design of low cost DC millivolt source project.

References


LM308 - Operational Amplifier
ICL8069 - Low Voltage Reference
LM78L05 - 3-Terminal 5V Positive Regulator
SS9011 – NPN General Purpose Transistor