Before & after the inductor, how does it look?

[Rick Law]

Folks, I need your experience and help again.  (Here is where I wish I have a scope).

(1)

With the LM2577 (or similar), Vcc is connected to 2577's Vin and via an inductor connected to 2577's SwitchOut.  That line continues to a diode then capacitor and Vout.

How would the signal look like at at the SwitchOut pin?  A more-or-less square wave at LM2577's internal 52kHz?

(attached schematic from app notes)


(2)
The LM2577 pin 1 is Compensation, what is it intended to compensate?

Thanks!
Rick

[c4757p]

How would the signal look like at at the SwitchOut pin?  A more-or-less square wave at LM2577's internal 52kHz?

More or less, but expect it to be very messy.

The LM2577 pin 1 is Compensation, what is it intended to compensate?

The feedback loop, which can sometimes become unstable without compensation, especially in current mode switchers like the LM2577.

[c4757p]

Page 19 of the datasheet explains a bit more, as well as giving a method for choosing them.

[Rick Law]

Page 19 of the datasheet explains a bit more, as well as giving a method for choosing them.

Thanks! (again)

I was using National Semiconductors datasheet and it is only 6 pages total with no info on compensation.

I just downloaded TI's datasheet and on page 19 - there it is all about compensation!  Even an inductor selection guide.  Something to read tonight.  Thanks again.

(Reminds me of a famous saying, "you don't know what you don't know...")

Rick

[c4757p]

I was using National Semiconductors datasheet and it is only 6 pages total with no info on compensation.

I just downloaded TI's datasheet and on page 19 - there it is all about compensation!

"The datasheet"... I forgot National was recently borged by TI and used to have shitty datasheets. I should have been more specific.