Technical Insights > Benchtop

Using Output Lists on a Multiple Output Power Supply

2018-09-27  |  10 min read 

List mode allows a power supply to act like a digital to analog converter, DAC. When using a power supply with multiple outputs the lists can be synchronized. The most common application is ramp each of the output voltages while making sure the DUT does not draw too much current.

Figure 1. Ramping the voltage on output one

Another application is to create timing, turning on parts of a module at different times. Power supplies that offer list mode vary in the maximum number of steps; 100 to 512. Keysight power supplies have several triggering options to allow multiple output power supplies or external instruments to synchronize with the list. Each step in a list typically includes a voltage level, current limit, time each point is held, and output triggers. Each step can include an output trigger at the beginning of a step (BOST) or the end of a step (EOST).

Figure 2. A list mode table of steps includes voltage, current, dwell time and external triggers (BOST & EOST) settings

Output List Property

List mode has several additional options shown in Figure 3. The options are described below in the order listed on the screen.

1) Select the voltage and current after the list is complete they can stay at the last step or return to their values before the list started.

2) You can choose to advance steps within a list based on a trigger or a dwell time. The power supply can be used to pace the test by selecting a dwell time. An external instrument can pace the test by choosing an external trigger.

3 and 4) The voltage and current need to be in list mode versus fixed mode. Fixed mode is the standard operating mode for a power supply where the voltage and current are set with the knob or programmed for a single value.

5) One of three triggers: a button press, a hardware trigger or bus trigger from the computer interface will start the list.

6) After a trigger is received a delay can be inserted before the first step is output.

7) The list can be repeated a finite number of times or set to continuous

Figure 3. Setting up the options for output list mode

Starting the list

The run/stopped button shown in Figure 2 is used to start the list. It is easy to modify the list from the front panel. Additional steps can be added, and existing steps can be changed, or deleted.

Figure 4. The power supply output using list mode

The list shown in Figure 2 includes a beginning-of-step-trigger, BOST in step three. Pin 1 of the digital I/O port is configured for trigger-out. Negative polarity is selected. Figure 5. shows the trigger signal.


Figure 5. The trigger signal generated in step three of the list

Getting the most out of 100 to 512 points

Most DACs or arbitrary waveform generators use a small consistent dwell time between points and have deep memory to store all the points. The key to getting the most out of 100 points is to specify the time between each point. For a signal that is not changing, a single point can be used with a long dwell time. A repetitive signal can be generated using the repeat count feature. Lastly, consider pacing the steps using external triggers. With a little creativity, a few points can go a long way.

Use of triggers

When you need an output list to follow external events closely, then a trigger-paced list is more appropriate. In a trigger-paced list, the list advances one step for each trigger received. As previously discussed, several sources can be selected to generate triggers. Triggers received during dwell periods are ignored. The minimum dwell period should be selected when using a trigger-paced list to avoid missing triggers.

Creating unique output lists for multiple output power supplies

Some multi-output power supplies support a unique output list per channel. The E36312A is a triple output power supply with three independent outputs. The power supply allows each output list to have a unique number of steps and dwell times. Each of the lists can be started independently or as a group.

Typically, the output lists are used together and would be set up with the same number of steps and common dwell times across outputs. As an example, each output starts with Step 0 which has a dwell time of 0.7 seconds. After the lists for each output have been created pressing the run button on each output will generate a List Waiting message. The List Waiting indicates that each of the lists is ready to start once a common trigger is received. A common trigger then starts the lists simultaneously.

Figure 6. Output lists for three outputs. Only output three’s properties are shown as all outputs will have the same settings

The common trigger can be a bus trigger or an external trigger. When using the power supply without a computer, an external trigger is used. The power supply can generate the external trigger using the digital I/O port. Pin 1 of the digital I/O port can be set as the trigger-in and Pin 2 can be used to create a trigger. A wire needs to connect Pin 1 and Pin 2. With the wire added Pin 1-In is equal to Pin 2-Out. Changing the state of Pin 2 from a zero to a one generates an external trigger.

Figure 7. Pin 2 is used to generate an external trigger to start the output lists

Figure 8. All three outputs stepping through their lists

All the voltage output lists stay in sync based on having the same dwell times.

Pacing each step with an external trigger

A second method is to configure output one to generate an external trigger at the beginning of each step and configure output two and three to advance on receiving a trigger. In this scenario, output one will pace output two and three.

Figure 9. Output one configured to output a trigger at the beginning of each step

External triggers are recognized after the dwell times are complete. Using the minimum dwell times on output two and three ensures the external triggers are acknowledged.

Figure 10. Output two and three are configured identically, with minimum dwell time and pace set for an external trigger

A wire on the digital I/O port connects Pin 1 and Pin 2. Pin 1 is set up as trigger-in, Pin 2 is trigger-out.

Figure 11. Digital I/O setup for trigger-in and trigger-out

Device protection

While the output lists are running the device, protections are running in the background. If an overvoltage or overcurrent condition is configured and tripped the output will shut off until the protection is reset. Likewise, each step contains a voltage, current combination. If the current is exceeded the power supply will change modes to a constant current. In our example, output one never reaches 6 V in step 4 as the current is exceeded.

A second example is powering up a new board. Most boards use lower currents at lower voltages. A board can be powered up with a low voltage while monitoring the current. If the current seems reasonable the voltage is increased. A list of voltages and currents can be used to power up a board. Restricting the current can protect the board from further damage.

Summary

List mode on a power supply is used to vary its output. Multiple output power supplies can be configured to run lists on each output. Lists can be synchronized with external devices or dwell times can be used to pace the output.

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