2017

June 2017

# TI-PMLK Buck Experiment Board - part 1c: 1st Experiment Measure

Posted by Jan Cumps Jun 24, 2017

I am a Road Tester of the TI-PMLK Buck Experiment Board: TPS54160 & LM3475.

It's an educational kit - board and book - to learn buck converter theory and practice.

Because it's an educational kit, I give minus points each time there's vendor lock-in .

I applied for the Road Test to check the educational value of the kit. The focus in this blog series will be on the Lab Manual and exercises.

In this blog, I measure the efficiency for Exercise 1.

# Doing the measurements

This is where the educational value of the kit is really excellent. The book doesn't discuss Buck regulator theory or measurement principles.

It assumes you have those skills. I think that's a good starting position in this case.

If you don't understand Buck converters or lack the skill of using multimeters and oscilloscopes, it doesn't really make sense to do these experiments.

They build upon your knowledge. They are not the base for  it.

Goal of Experiment 1:

The goal of this experiment is to investigate how the efficiency of a buck regulator depends on the line and load conditions and on the switching frequency.

The document reviews the parameters that play a role in efficiency, shows the components that have a loss independent of load and components that have load dependent losses.

The exercise is to measure input and output power with varying load, for an input voltage of 6 and 24 volt and calculate efficiency.

Then you have to compare that with the efficiency calculation. You get enough help in the doc to get that calculated.

Simulation affectionados (yes you Jon) may want to run it through Spice or the likes.

Then follow the steps to set everything up and perform the exercise (click to enlarge).

You record both calculated and measured values in a table, for those efficiency and loss tests.

Here's a few of my measurement recordings and some scope captures:

• Input 6 Output current 0.8 A

• Input 24V Output current 0.8 A

Here's what the manual shows for 24V 1A. It's obvious that my current measurement method (blue in the capure above vs. green in the TI manual) is not up to the game.

What I haven't done yet is to measure the behaviour when the regulator operates in non-continuous mode.

That's a todo for the next article. I'll also comment on educational value and vendor lock-in score of the kit (spoiler: high and low )

# TI-PMLK Buck Experiment Board - part 1b: 1st Experiment Lab Setup

Posted by Jan Cumps Jun 24, 2017

I am a Road Tester of the TI-PMLK Buck Experiment Board: TPS54160 & LM3475.

It's an educational kit - board and book - to learn buck converter theory and practice.

Because it's an educational kit, I give minus points each time there's vendor lock-in .

I applied for the Road Test to check the educational value of the kit. The focus in this blog series will be on the Lab Manual and exercises.

In this blog, I set up the test equipment for Experiment 1

# Experiment 1: Impact of Load, Input Voltage and Switching Frequency on Efficiency

In this exercise we'll measure the efficiency a few times under changing conditions.

The tutorial advises this Lab setup:

I'm replacing the input current meter with the display of my power supply. The input voltage I've measured with the DMM.

The load is a string of 0R1 and R resistors that form 3R3 in total. That's 1A of output current for this 3V3 circuit.

My biggest miss is a current probe. This is used in the circuit to measure the current racing trough the inductor.

I first tried if I could put two oscilloscope probes on TP10 and TP11 of the circuit.

Then I tried to use the Math function of my scope to show the difference between the two.

It turns out (as expected really) that I don't get enough drop over 0R01 resistor R5 to get a signal that's above the noise floor.

What works better is the second thing I tried: wind a coil of isolated wire around R5 and try to steal the current that way.

This works way better. I can get a view of the current in the circuit's switching node on my oscilloscope.

Way too course to do a good measurement but it does the job of visualising what happens.

The switch node current is the blue trace on the capture below:

If you have a better idea on how I can show the switch node current, please comment below.

I measure output voltage with the DMM, and output current by putting my DMM over one of the load resistors in the chain + Ohm's Law.

(in the next blog you can see that I stepped away from measuring current over a series resistor and used a current meter. See comments below)

# TI-PMLK Buck Experiment Board - part 1a: 1st Experiment Set-up

Posted by Jan Cumps Jun 23, 2017

I am a Road Tester of the TI-PMLK Buck Experiment Board: TPS54160 & LM3475.

It's an educational kit - board and book - to learn buck converter theory and practice.

Because it's an educational kit, I give minus points each time there's vendor lock-in .

I applied for the Road Test to check the educational value of the kit. The focus in this blog series will be on the Lab Manual and exercises.

In this first blog, I'll try exercise 1.

# Power Management Lab Kit Buck Experiment Book

The manual is set up as a set of lab experiments.

All exercises follow the same steps: theory, set-up and measure. Each experiment closes with a review discussion and a dig into the results.

The first experiments of each kit review the basic behaviour:

"What happens with the efficiency of the regulator if we change input voltage, the load at the output or the switching frequency?"

I am actually going to do the test and will do an attempt to calculate that efficiency.

# Lab Set-up

 Lab requirements The kit expects that you have a decent lab. I don't.For these exercises that I'm doing here, my set-up will do.You can get almost all educational value out of this kit with a modest setup.If you're an electronics student, you can use your college or uni lab.Home testers will have to be inventive and will have to learn how to perform measurements in a less optimal situation.That's a good skill to have too. Here are the recommended Lab specs for the kit:DC power supply 0-50V/4A with dynamic voltage mode capabilityDC electronic load 20V/10A with dynamic current mode capability4 digital multimeters with 4 1/2-digit resolution250MHz 4-channels Digital Oscilloscope + 2 current probes 20A/50MHzI have none of these   edit: the author of the book has addressed most of these remarks.

My set-up for today's case will be:

• Rigol DP832A DC power supply 0-60V/3A or 0-30V /6A
• Mix of cement power resistors 0R1 and 1R, 10W
• 1 digital multimeter Brymen BM235
• RIGOL DS1054Z 50 MHz 4-channels Digital Oscilloscope, no current probes

Obviously, this is a much humbler lab than the one TI prescribes. If you feel that I can't perform this exercise correctly with my current set-up, feel free to mail me the missing instruments .

In the next blog post, it's connect and measure time. Hang on. In the meantime read the lab manual. You can download it from the element14 community.

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