In part 1 of” How fundamental features of DC power
supplies impact your test throughput” (click here to access) I shared
definitions of some of the fundamental power supply features that impact test
throughput, including:
- Command processing time
- Up-programming response time
- Down-programming response time
Another fundamental DC power supply feature impacting test
throughput is its measurement time. There are actually two aspects to a DC
power supply’s measurement time as depicted in Figure 1:
- Measurement settling time
- Measurement integration time
Figure 1: DC power supply measurement time
A good indicator of a DC power supply having a high performance
measurement system is having programmable measurement integration time, or
aperture time, often programmed in power line cycles (PLCs). One reason for having a programmable
integration time is for minimizing any 50 or 60 Hz AC line ripple getting into
the DC measurement, by setting the time one or more multiples of a PLC. Setting the time to 1 PLC provides good
ripple rejection with relatively good throughput. When AC line ripple is not an
issue the integration time can be set even smaller than 1 PLC, further reducing
measurement time. When the DC power supply has a programmable measurement
integration time it will no doubt also have a fast-responding measurement
system as well, typically just milliseconds, to complement the higher
achievable throughput with programmable measurement integration time.
In comparison basic DC power supplies commonly use a 100 millisecond
fixed integration time to support AC ripple rejection for both 50 and 60 Hz
line frequencies. They also have low bandwidth, slow-responding measurement
systems, which can long time to settle after any step change in loading, before
a valid measurement can be taken.
We have just introduced our Advanced Power System (APS) DC power
supplies. This is a family of high-performance, high power (1 and 2 kW) DC
power supplies designed to address the most demanding test challenges. These
fundamental throughput-related features for APS are typically more than two
orders of magnitude faster compared to more basic-performance DC power supplies,
providing much better throughput in manufacturing test. A colleague of mine
recently posted details of their introduction on his “General Purpose
Electronic Test Equipment (GEPETE)” blog (click here to access) which I believe
you will find of interest. Included in this introduction is a link on
throughput that takes you to a series of application briefs I have written that
go into more detail on improving test throughput with the DC power supply,
which you may find very useful.
So how much test throughput improvement might you expect to see by
switching from a basic-performance DC source to a high-performance DC source?
Well, it really depends on how much the testing makes use of the DC power
supply. If it only uses the power supply to provide a fixed DC bias to the
device under test (DUT) that never changes for the duration of the test then it
will not make a significant difference. More often than not however, a DUT is
tested at several bias voltages with several current drain measurements taken
for the various bias voltage settings and DUT operating modes. This can add up
to a considerable amount of test time. In this case a high-performance DC power
supply can more than pay for itself many times over due to improved test
throughput. To get an idea of the kind
of difference a high-performance DC power supply can make I set up a representative
benchmark test It compares the throughput performance one of our new APS DC
power supplies to that of a more basic-performance power supply. If you are interested in finding out how much
difference it made, I made a video of this benchmark testing, entitled “Increasing
Test Throughput with Advanced Power System” (click here to access). All I am
going to say here is it is an impressive difference but you will need to watch the
video to see how much difference!