Is it possible to build a SEPIC from a MC33063?

Luis Filipe Rossi

Other Parts Discussed in Thread: TPS40210, TPS40200

Is it possible o build a sepic using a MC33063? If yes, how? If not, can any one sugest me some very cheap IC, with high availability on the market for a 9-27V input, 14.1V output 1A ***? The current can be a little less like 0.8A if needed. Thank you!

Thank you!

over 13 years ago

0 Jeff F over 13 years ago

TI__Guru*** 143870 points

It is possible but somewhat difficult, even for our most experienced designers. We have no appnote or computational tool that is specific to the MC33063 running as a SEPIC. The MC33063 uses hysteretic control.

You might consider the TPS40210 as a continuous mode SEPIC. The link here: http://focus.ti.com/lit/an/slyt309/slyt309.pdf gives the basic equations for sizing the power stage components. The example uses another IC and so the explanation on compensation is not relevant. The TPS40210 uses voltage mode control so compensating the control loop of the SEPIC converter can be tricky.

Or you might consider the TPS40200 as a ZETA converter as explained here: http://focus.ti.com/lit/an/slyt372/slyt372.pdf. Compared to a SEPIC, the ZETA will require a much larger flying capacitor than the SEPIC but should be a bit easier to compensate.

0 Luis Filipe Rossi over 13 years ago in reply to Jeff F

Expert 1035 points

Thank you but why is so hard to perfrom the compensation. Is there any other IC from texas that might be simple to designe a SEPIC with the specs i wrote before? But be possible is nothing with high availability. I need something that i could find easily on any distributor.

Thank you!

0 Jeff F over 13 years ago in reply to Luis Filipe Rossi

TI__Guru*** 143870 points

A SEPIC converter is a very complex dc/dc converter. Using a fixed frequency PWM converter results in several small signal poles and zeros, both real and complex. Using a hysteretic converter like the MC33063 will not require compensation but careful component selection.

0 Luis Filipe Rossi over 13 years ago in reply to Jeff F

Expert 1035 points

Which kind of converter is better for making a SEPIC? Is SEPIC a good choice for a 9-27V input.. 14.1V Fixed on the output.. 1A? Good regulation is not a requirement as it wil be further regulated. Any good reference about designing SEPICs?

Thank you!

0 Jeff F over 13 years ago in reply to Luis Filipe Rossi

TI__Guru*** 143870 points

SEPIC is valid topology and is a good choice for your application. There are simply few tools available to help.

0 Luis Filipe Rossi over 13 years ago in reply to Jeff F

Expert 1035 points

I was looking on some AN i found on the internet about using the MC34063 as a Step-Up/Down Switching regulator. What kind of problems i am going to face on this kind of deisgn, specially with my requiriments?

Thank you!

Power management

Power management forum

Is it possible to build a SEPIC from a MC33063?