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To Double or not to double?

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NivagSwerdna:
I built myself a 35V Boost regulator but have discovered I would really be much better off with 70V...

I came across this (from Pile o Poo)...



Now my boost regulator looks very much like...



i.e. it has an inductor and a diode and a mosfet switch.... So with 2 Capacitors and 2 Diodes I could get my 35V to 70?

I need around 3W... i.e. 50mA at 70V

Or should I go back to the drawing board and design a 70V regulator?

Thanks in advance



james_s:
Can you not just make a few tweaks to the inductor size and feedback loop to get 70V? Boost converters often give you quite a bit of wiggle room.

MagicSmoker:

--- Quote from: NivagSwerdna on July 17, 2019, 03:46:31 pm ---I built myself a 35V Boost regulator but have discovered I would really be much better off with 70V...
...
I need around 3W... i.e. 50mA at 70V

--- End quote ---

You can do this easily enough with a boost, and you can use your existing circuit if you change the feedback resistor ratio, the timing capacitor value and the boost inductor. See OnSemi AN920 for a comprehensive explanation of how to do the above.

Oh, and be wary of saddling the FB pin with too much capacitance - the '34063 is a hysteretic controller and does not need frequency compensation, so adding a capacitor to the FB pin just slows down its response to voltage over/undershoot. That said, 47-100pF on the FB can help suppress early pulse termination from noise, so don't delete it entirely.



SiliconWizard:
http://www.ti.com/product/LM5001

NivagSwerdna:
Sadly I opted for a chip TPS61175 with an inbuilt switch rated at 38V. (I said it was alike not the same  :) )

I can redesign but just wondered about the merits and weaknesses of doubling.

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