Related
Recommended

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

jancumps

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)

 

 

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

Anonymous
  • in reply to jancumps

    Jan, I saw. This depends on the power level range I suppose. With low powering the method seems working as there is not the heating risk. I have not cited this aspect but iti s true what you say about the dramatic temperature influence. I was thinking on few mA order. Or this occurs anyway?

     

    Enrico

  • in reply to DAB

    Thank you Don.

    The 2 current probes required for this board are off-circuit. It's one of those inductive oscilloscope add-ons that you clamp on a wire and that shows the waveform on your oscilloscope.

     

     

    With this amplifier:

  • in reply to balearicdynamics

    Enrico Miglino wrote:

     

    Thank you Jan. As you can see my knowledge in the powering world is really terrible !

     

    Just a note instead. I have used 1 Ohm 150 W resistors to calculate the current. I thought that it was a very crap method instead I see that you too are using something similar. So is it reliable ? It seems I have not adopted a so bad solution...

     

    Enrico

    In the next blog you can see that I stepped away from this method and used a current meter in series with the output. The drift of my resistors was way too high to get a decent current sample..

    After running warm (not even hot) my 1R power resistor measured up to 2R. So I had to change strategy.

  • Great post Jan.

     

    Yes, without an in circuit current probe, you are stuck pulling off voltage measurements and estimating the current flow.

     

    DAB

  • in reply to jancumps

    Thank you Jan. As you can see my knowledge in the powering world is really terrible !

     

    Just a note instead. I have used 1 Ohm 150 W resistors to calculate the current. I thought that it was a very crap method instead I see that you too are using something similar. So is it reliable ? It seems I have not adopted a so bad solution...

     

    Enrico