Many op-amp circuits used in analog applications, such as signal conditioning for high bit count analog-to-digital converters require the use of both positive and negative power supply voltages, as shown in Figure 1. Supplying both positive and negative voltages allows input signals and output signals to swing both positive and negative. You could power these circuits with an adjustable power supply with two outputs and adjust them separately—one to the positive rail voltage, say +12 VDC or +15 VDC and the other to a similar negative voltage.
The problem with this approach is that it is cumbersome to adjust both supplies simultaneously and to get the two output voltages to be equal to one another. Another problem that can occur is that the op amp may “latch up” if the power-up sequence is not coordinated properly. This can damage the op amp or prevent it from operating correctly.
A better approach is to use an adjustable power supply with tracking outputs, such as the Sorensen XBT Series. The XBT Series provides three output channels, and channels 1 and 2 can be configured for parallel, series, or tracking operation. In tracking mode, channels 1 and 2 provide the same (but opposite polarity) outputs. In addition, the outputs can be isolated from one another, if desired. These two channels can supply 0 – 32 VDC with a maximum current of 3 A. Tracking accuracy is ± 0.02% + 10 mV.
It’s very easy to set up output tracking. From the front panel, simply press the CONFIG key, select TRACKing with the rotary control, then press the rotary control to turn tracking on or off. To turn tracking on or off via computer control, simply issue the SCPI command OUT:TRACK. Once tracking is turned on, Channel 2 will have the same voltage and current settings as Channel 1.
One of the ways that you might use this feature is to test the sensitivity of your circuit to power supply voltage. Programatically, you could ramp the power supply voltage up and down from say 9 VDC to 15 VDC in steps, performing a functional test at each step.
Keep in mind that the Sorensen XBT is a precision power supply. When powering your circuit from the power supply in your product, the performance of the circuit may vary from the performance you observe with the benchtop power supply. That being the case, it’s also necessary to thoroughly test your circuit with the production power supply.
For more information on adjustable power supplies and how to use tracking outputs, contact AMETEK Programmable Power. You can send an e-mail to firstname.lastname@example.org or phone 800-733-5427.