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  • Author Author: Jan Cumps
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TI-PMLK Buck Experiment Board - part 1b: 1st Experiment Lab Setup

Jan Cumps

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 image .

 

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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:

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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.

 

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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.

 

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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.

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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:

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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)

 

 

Related Blog
1a: 1st Experiment Set-up
1b: 1st Experiment Lab Setup
1c: 1st Experiment Measure
2: Educational Value

Road Test: TI-PMLK Buck Experiment Board: TPS54160 & LM3475

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