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LM723CN as switching -Hz? -how make higher Hz? Current limiting (formula) Adjust all the way? -how?

M E62
Prodigy 70 points
Other Parts Discussed in Thread: LM723

Hi there!

I'm thinking of this pic:

-Whitch switching frequens does this have?

-How do i make the frequens higher?

The current limit is 2 A,

-How do i make it higher?   ..or lower?

The formula is:

-Rsc?   -correct?   -...or should it say "Rcs"?

There are 2 schematics, one for 2 - 7 Volts, one for 7 - 37 Volts.

-Is there any possibility to make one for 2 - 37 Volts?

If it is: -Where can i find it?   (i'd prefere a switching one, but it is nessecery)

In the PDF it says "Figures in parentheses may be used if R1/R2 divider is placed on opposite input of error amp."

-What is an "error amp."?

-How would the schematics look like if i do so?   ( download and draw on the pic!)

D1   1N2071
T1   2N5455
T2   2N5153

-Is there any alternative that would work in this thing?

In one formula:

I know that inside the paranteses is to be done first, but what about   ;   ?

-What does   ;   mean in a formula?

Thank you very much!

  • 0
    TI__Expert 3870 points
    Hi - The Team is presently on Holiday vacation, please allow us a couple of more days to answer to your post.
    Regards,
    -JPF
  • 0
    TI__Expert 4365 points
    Hello M E62,

    Unfortunately your schematics and equations did not get attached properly to your post.
    I must first point out that the LM723 is a linear regulator that is most commonly used as a linear regulator controller. Many many millions of these have been placed into service as linear regulators over the years and there are many second sources to this device in the industry.
    While there are in fact some suggested applications in the data sheet that hint that you can apply it in a switching application I highly suggest that it is not worth the effort. The LM723 was introduced in the early 1970s when there were very few choices for either linear or switching regulator ICs.
    Since that device was introduced, countless numbers of more appropriate devices have been introduced to create well behaved and predictable switching regulators that will solve your application. However, I only see your range of 2-37 which I must guess is an input range (or is this an output range?)

    I highly suggest going to the TI website and finding the Webench device selection and simulation tool. It will quickly suggest suitable devices that can be simulated and adjusted for your application.

    To more specifically answer some of you questions: The LM723 does not have an internal oscillator. Therefore, if you do succeed in getting it to oscillate, its frequency will be determined by all things external and internal that create a delay. In terms of current limit; I certainly recommend that applications have a current limit of some sort, appropriate for the topology and application. A switching regulator based on the LM723 would not be well advised in this day and age (or even in the 1970s). One overriding point is that this is a commodity device manufactured by many companies. It is unlikely the internal delays would be at all close to each other with different manufacturers versions. Even with a single manufacturer it is unlikely you could create a consistent reliable design that is not also dependent on variations in external components.

    If you have any LM723 devices on hand; they work very well as linear regulator controllers.