Designing 5A Boost converter

[Bakmeel]

To all experts:

For a school project, we are designing a dynamometer based on a DC motor. For this pupose we need a boost converter, working in current mode control, that can draw 5A continuous from a source generating 6 to 35V DC.

I am stuck on a fundamental design problem: the boost converter coil. How can I determine how big it needs to be? Switching frequency will be around 500kHz

Second, the DC engine itself physically contains a rather large inductance too. Measurments with a wheatstone bridge give an inductance of around 8.8 mH. Could I try to use the engine's self inductance for my purpose?

All other help would also be appreciated. I'm sure I haven't thought of everything.

Yours,
Bouke

[Sch3mat1c]

Er... and why doesn't a 5A CCS do the job? Maybe some filtering, 10,000uF or so on it?

Tim

[Bakmeel]

Because the goal is to regenerate the power into the mains. The regeneration part is not our job to do, but we must build something like a controllable "current pump", highly efficient, etc. For now we will dissipate with a CCS behind that, but the CCS wasn't the problem

Because a boost converter can draw a "programmable current" it is what we need.

[Ouroboros]

For help with the boost converter (and other simple SMPSU types), have a look at

http://henry.fbe.fh-darmstadt.de/smps_e/#smps

This site has some very useful on-line design aids and simulation software.

Your input varies from 6 to 35V. What are you intending to boost this up to?

For simple to use boost circuits, check out the 3843 control chips (many sources, UC3843, TL3843 etc or the UCC3800 range. The TI web site and the STmicro site have data sheets and app notes.

If you have a separate low-current 12V supply to power the control chip, leaving the 6-35V to feed the boost inductor and switching FET, then it makes life easier.

Best of luck,
Chris.