DC Voltage and Current Source

Wichit Sirichote, kswichit@kmitl.ac.th

A reference volatge and current source for testing data converter and analog amplifier.

A simple circuit built with TI LinCMOS opamp, TLC254C provides multiple outputs: +2.5V, 0 to +2.5V and 0 to 250uA. The circuit is operated with 9V battery.

Figure 1: Circuit built with universal pcb.

The LM336 provides +2.5V reference voltage. U1A buffers the reference voltage for U1B and U1D. R2 is 25 turns precision resister. It is simple voltage divider providing adjustable 0 to +2.5V for U1B. U1C is voltage controlled current source. The output current will be V(noninverting)/R3. Since the input voltage to the U1C is adjustable from 0-2.5V, U1C will then drive RLoad with 0-250uA. The maximum load is approx. 14k when uses 9V battery. U1D buffers again the +2.5V.
Figure 2: Schematic of DC voltage and current source.

I got the sample chip from Texas Instrument. It was surface mount device. To solder the chip, I extended the tiny leg with wire cut from resister, quite difficult. The reference voltage LM336 is TO92 package shown in the left-hand.

The circuit draws approx. 5mA. If you find the low bias for DC applications, TLC254A, it would draw only 50uA!

Figure 3: The chip, TLC254C is surface mount!

28 Aug 2005

recovered 17 December 2015