Author Topic: Keysight E36103A PSU, Teardown and Measurements  (Read 4100 times)

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Offline alm

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Re: Keysight E36103A PSU, Teardown and Measurements
« Reply #25 on: July 26, 2017, 12:36:30 am »
The voltage between the force and sense terminals is usually limited to something like 0.5 - 1 V (check the manual of that particular power supply). So a 100 Ohm resistor might work if you are sure the peak power draw is below 5 mA. Obviously this would tie up a DMM for the duration of the measurement.
 

Offline nctnico

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Re: Keysight E36103A PSU, Teardown and Measurements
« Reply #26 on: July 26, 2017, 03:11:26 am »
The voltage between the force and sense terminals is usually limited to something like 0.5 - 1 V (check the manual of that particular power supply). So a 100 Ohm resistor might work if you are sure the peak power draw is below 5 mA. Obviously this would tie up a DMM for the duration of the measurement.
Didn't you read my previous posting? Think about what happens with the output capacitors in the power supply and you'll see it won't work with such high resistances in series with the load! The E36103A is rated for 2V max. compensation (1V in each lead). Because this is a 2A PSU this translates to a maximum (total) resistance in series with the load of 1 Ohm.
« Last Edit: July 26, 2017, 03:16:12 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline alm

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Re: Keysight E36103A PSU, Teardown and Measurements
« Reply #27 on: July 26, 2017, 04:36:57 am »
If they wanted to limit the resistance between force and sense, they would have specified a maximum resistance. But they specified a maximum voltage. As long as your I*R drop does not exceed this voltage, you are within their specifications. As for the output cap, I am pretty sure these supplies have an active down programmer. Without that, I agree that transient response will be degraded. How much output capacitance do these power supplies have? I expect output capacitance to be quite low in a modern design.

For best transient response, Keysight suggests (page 15) a capacitor at the device under test. Obviously that would degrade the current measurement bandwidth. This document discusses this issue in some detail (including a discussion of bypassing at the DUT).
 

Offline nctnico

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Re: Keysight E36103A PSU, Teardown and Measurements
« Reply #28 on: July 26, 2017, 06:27:38 pm »
Decoupling is tricky because most typical decoupling capacitors leak. Electrolytics can leak up to tens of uA. Ceramics are in the nA range.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline anotherlin

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Re: Keysight E36103A PSU, Teardown and Measurements
« Reply #29 on: July 26, 2017, 07:42:19 pm »
Linear power supply with constant current capabilities must have a current sense resistor anyway for the purpose of current regulation.
And they of course take great care during design so that sense resistor have minimum effect on the regulated output.
So why not do the thing from the ground up, and have precision current measuring from it, instead of relying on external measuring devices, which is more error prone and requires care to obtain precise measuring.

Of course, this is may be more costly. And I fully understand that people having a PSU without precision current measurement but a 6.5 or 5.5 digit bench DMM, don't want to buy an extra PSU, and would prefer to make the most of the (costly) equipment they already own.
"Lots of people have made $100K or more mistakes and didn't get the boot. It's called training, why fire them after such an expensive lesson?" -- EEVblog Electronics Community Forum
 

Offline alm

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Re: Keysight E36103A PSU, Teardown and Measurements
« Reply #30 on: July 26, 2017, 08:22:49 pm »
Assuming you do not need said DMM for something else. If you do, for example to measure something else in your device under test, then buying a power supply that can do the measurement on its own rather than than buying a cheaper power supply + another DMM may make sense.
 


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