Tutorial video, gain/phase of a flyback using a function generator and scope

[rbola35618]

Poor man's frequency response analyzer(Gain and Phase measurement of a flyback supply)

This video is a follow up to a previous video where I used a Venable Frequency Response Analyzer (FRA). Most FRA are out of the budget of most small business or hobbyist. However, you can use a function generator, an injection transformer, and a scope to measure the stability of a power supply such as a flyback.
By injecting a signal and measuring the amplitude and the phase delay, you can measure three critical power supply specifications such as the crossover frequency, phase margin, and gain margin.

You can use any wide band transformer as long as the transformer bandwidth is 1 MHz. The only negative of using an off the self transformer is that they have high capacitance from the primary to secondary in the 1.5 nF range. However, if you can wind your own transformer and use a split bobbing, you can greatly reduce the primary to secondary capacitance. The transformer that I wound measured a total of 15 pF between the primary and secondary

Question and comments are welcomed!

[Tita]

Good work.. i like the video!

[rbola35618]

Thank you guys for the kind comments.

Best regard,

Robert Bolanos

[Kevin.D]

A Nice (and rare) video demonstration of this technique ,thanks .Would of been better if you had discussed in more detail why you chose those specific values that you chose to use for the  injection transformer and the injection resistor .
But still really usefull ,even  just to show people you dont need multi thousand dollar equipment to  do basic stabiltity analysis .

[rbola35618]

Kevin,

That is great feedback. I will will anotate that on the video.  One other thing that I forgot to mention is to make sure the signal level is increased until the sinewave starts to get distorded. The is suppose to be a small signal measurement. When the sinewave distorts, then you have too much signal and you are operating in the large signal mode.

The injection transformer is a copy of the Venable injection transformer except that I used a bigger p-core. The capacitor should be a non polarized capacitor so the you can use it on both negative and positive supplies.

I will annotate these facts on the video tonight.  Again, thanks for the feedback Kevin

Best regard,
Robert Bolanos

[rbola35618]

I found an affordable FRA on the Cleverscope website.  I think this is a game changer for those that are interested in a FRA. Most of the FRA out there cost from 5K to 35K.  The Cleverscope is a fraction of its competitors at 1500. This is well within my budget.