How well does a DC-DC converter work in the real world? Load regulation and line regulation tests will tell you!
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Ideally, when you set your DC power supply to a certain voltage, it will maintain that voltage and have little or no noise. However, many external conditions can affect the power supply's output. Since, a power supply is used to power a device under test (DUT), any variations or noise in the output is directly coupled to the DUT. Following are some of the commons sources of unwanted power supply signals, and how they are specified in a data sheet.
Loads often require varying amounts of current. Load regulation is a power supply's ability to maintain a constant voltage regardless of the demands of the load for more or less current. A power supply's load regulation specification tells how accurately the voltage will be maintained for example the E3632A load regulation is specified as 0.01% of output plus 2mV. A power supply's transient response specification tells how fast the power supply can return to the desired voltage for example, 50mseconds for a large change in the load.
Changes in the AC line voltage can affect the output of a DC power supply. In some regions, AC line voltages can vary greatly. A motor or piece of large equipment can cause voltage to drop in power lines when it pulls excessive current. The ability to maintain a set DC voltage during a change in line voltage is specified as line regulation. Line regulation is typically specified in two ways. First the power supply will only function properly if the AC line voltage is close to the proper voltage, typically ± 10%. Line regulation also affects the output accuracy and is specified as a percent of output with an offset.
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Today we’re exploring how to test a DC to DC converter. We’re going to use a 60W, 24 V to 12 V DC converter. We’re going to stress the converter in two ways – first we’ll do a line regulation test, which means we’re going to vary the input power and see how it affects the output. Second, we’re going to do a load regulation test. For this test we’ll vary the load on the converter’s outputs and see how the output power changes.
To do that, Bill brought along a power analyzer, which is essentially a fancy control system with a chassis that you can load modules into. This one has a 100 W supply module that will supply power to the converter’s inputs, and a 100 W electronic load module which we’ll use to sink power from the converter’s outputs. To control it all, we’ll use the new Advanced Power Control and Analysis Software, which is part of the Pathwave BenchVue platform. This makes it easy for us to control the supply and load dynamically.
The converter has two sets of inputs and two sets of outputs so we can do 4-wire sensing: one set carries power, and the other set allows the system to readback the values and adjust its outputs.
For our first test – line regulation – the power supply will output a series of different power levels using an output list. We’re then measuring the converter’s output to see how it changes.
We can select a built-in arb to turn on the load during the test -A pulse 0 to 3A .4s,9s,.6s
The electronic load has four modes of operation – voltage, resistance, power, or current
Turning of the load after 9 seconds will remove the load from the converter while it still has power.
The last thing to do once you have this setup is to run it for a long period. Ideally you also don’t have to sit there and watch it run for 3 or 6 hours, so you can use data logging. This lets you set it, walk away, and see how it performs for a while.
And, if something looks funky or you need to get documentation setup, you can export just that piece of the record – historically you’d have to export whole thing.
This power analyzer also has a scope capability. You can trigger and zoom in on short events like an edge and get a peek into your system without having to pull out an actual scope.
Another thing you can do with this is setup a level trigger and have it do something if the trigger condition is met. For example, you could shut down your outputs if the voltage or current gets too high – this could definitely save your device if things go south.
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