Hi,
I have built a Zeta converter for MPPT charging, based on AN1521 from Microchip. I have attached the drawings and board of my circuit.
It works okay (voltage and current regulation is working), with the exception of my inductors going a bit warm, even on low currents, where the inductor L2 rises to about 10 degrees above ambient. I have yet to test it at higher currents than 1.2A on the output.

I attached a 1ohm resistor in series with the ground input, in order to measure input current waveform, to see if there was any abnormal currents going through the circuit. Attached is the measurement of this, where the yellow line is gate voltage on Top FET, blue is voltage over the current shunt.
The current peak during low time on top fet is when Q2 turn on I guess. The PWM signal is made by the usage of Microchips NCO unit, and have a fixed on time of 2uS.


The inductor is bought from ebay (same as thisone: https://www.ebay.com/itm/2pcs-Toroi...mm-x-14-6mm-/152824565929?hash=item23950dd0a9), and is not coupled as in Microchip's design. I have re-wound them to be 20uH due to this, and not 10uH as per Microchip design.

So, finally to the question: Why is the inductor getting hot even at these low currents? I do not think it should be like this.
Input and output capacitors C5-7 are 680uF, and coupling capacitors C1-4 are 470uF.

BR
Vidar

 

Hi, that color pattern reminds me of the inductor I had that seemed to have a similar problem.

 

Hi MSFTF,
what do you mean with "color pattern"? Is it the plot from the Scope you are referring to?
Did you find any solution to your problem?

 

It is the color pattern of the inductor core. Yellow on one side and white on the other side. I was pretty baffled by why they were getting so hot. I just gave up on them. Sorry I couldn't help more.