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So right now I have a boost converter with a capacitor at the output as energy storage. My idea was to use a comparator (DC) comparing capacitor Voltage vs. reference, and the output was connected to the transistor (switch), so the load would be charged with the energy, but it doesn't seem to work as intended. Any suggestions?

Forgot to add: imgur.com/a/FbHe7 I want R2 to enable a switch so there is a connection to R1, when a certain voltage on the capacitor is reached

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  • \$\begingroup\$ I suggest you add a schematic so we have a clue.... \$\endgroup\$
    – Trevor_G
    Jun 8 '17 at 15:01
  • \$\begingroup\$ So this: imgur.com/a/FbHe7 I want R2 to enable a switch so there is a connection to R1, when a certain voltage on the capacitor is reached. \$\endgroup\$
    – dnopas
    Jun 8 '17 at 15:16
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Put a P-channel MOSFET with its source connected to boost capacitor and drain to load. Gate drive should be inverted - low=active, high=inactive. This can be done by OpAmp's inputs.

schematic

simulate this circuit – Schematic created using CircuitLab

Values were not calculated!

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  • \$\begingroup\$ Thanks for the answer. I'll try it. What about using a 555 timer, would that be working? \$\endgroup\$
    – dnopas
    Jun 8 '17 at 17:02
  • \$\begingroup\$ @dnopas - I don't understand - what will 555 do? \$\endgroup\$ Jun 8 '17 at 17:08
  • \$\begingroup\$ Setting it up as a monostable multivibrator, then it would discharge when the external capacitor reached 2/3 of the supply voltage. \$\endgroup\$
    – dnopas
    Jun 8 '17 at 17:18
  • \$\begingroup\$ @dnopas Well... it's kind of funky.. but why not :) You could tie pins 2&6 to boost cap and ouput pin 3 to drive PMOS gate (or even use pin 7 - discharge). Remember that 555 needs a 10nF cap on pin5. \$\endgroup\$ Jun 8 '17 at 17:25
  • \$\begingroup\$ The reasonable question is why do you need boost if you already have a higher voltage to supply 555, but it goes really out of scope of the initial question. \$\endgroup\$ Jun 8 '17 at 17:26

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