I was experimenting with a low watt boost converter,12V to 100V,50mA using the venerable MC34063A and an external MOSFET switch..I calculated the inductor value to be about 100uH.So I made two inductors using a drum core and toroid ring,both of which are 100uH.The drum core works well,but under load the toroid drops to 60V or so. Is the toroid saturating? If so ,should i use a larger toroid to overcome this problem? TIA.

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    \$\begingroup\$ Show schematic. Show core calculation LI=NAB. \$\endgroup\$ – winny Mar 23 '18 at 18:30
  • \$\begingroup\$ Thanks for the reply,winny.The schematic is exactly the same as : threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit. I did not do any calculations for the core,just used some inductor cores lying around and wound wire to get the required inductance. \$\endgroup\$ – EmbSysDev Mar 23 '18 at 19:18
  • \$\begingroup\$ There’s your problem! Now calculate the peak flux density and peak current ripple of your converter. \$\endgroup\$ – winny Mar 24 '18 at 6:27

A 5:1 ratio is already on top of what is possible with a simple boost converter. The turn-off time of your switch has to be extremely short for higher ratios, otherwise you won't get a high boost. A flyback topology is often simpler to implement.

  • \$\begingroup\$ Thanks Janka.Yes,am aware of that. My application needs less current ,so as is,my requirement is fulfilled.Was just looking for some empirical suggestions,on sizing toroids. \$\endgroup\$ – EmbSysDev Mar 23 '18 at 19:17
  • \$\begingroup\$ What material is the toroid core? \$\endgroup\$ – Janka Mar 23 '18 at 19:21
  • \$\begingroup\$ Its ferrite , about 16 mm OD,and height about 6mm.Putting 2 turns(2 passes of wire through the center) gives about 15uH. \$\endgroup\$ – EmbSysDev Mar 23 '18 at 19:32

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