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Refering to this post, I changed mic5156 to mic5158 (datasheet) and this mos.

I wired it several times as the datasheet shows but I can't get any regulated voltage. In order to understand what happens, I removed the mos and put a potentiometer instead of the divider. The result is (IMHO) what it should: The gate voltage is maximum when the divider is below the 1.235V reference voltage the goes to "nearly zero" (in fact around 1 v) when the divider is above 1.235V.

Yellow: divider

Green: Vcp

Orange: Vgate

enter image description here

Then, I rebuild the circuit with the mos and did the following measurement:

Yellow: divider

Green: Vcp

Orange: Vgate

Light blue: Vgs

Starting with a 1A load, I raised it until 10A.

Some observations:

  • The output voltage goes from "too high" to "too low". The voltage is correct only when on marker 2 in the below capture.

  • The pump voltage falls to 0v on marker 1.

enter image description here

I definitely don't understand what happen. Did I do a wrong choice with the mos? Should I work around capacitors of the charge pump? Is there a reason why the gate voltage in first test goes to "nearly 0v" and not 0v? Is it a regular behaviour that the charge pump voltage goes to 0? I supposed that It should stay always high, only the Vgs changes but may be I"m wrong.

A lot of interrogations...

[update]

Schematic:

enter image description here

Breadboard:

enter image description here

[Update]

I changed MOS for IRF610 (datasheet) and... It works! The specs does not fit my needs but the voltage is regulated with. Still wonder which characteristic makes the original mos unsuitable.

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  • \$\begingroup\$ Since you are not sure you wire it correctly... why don't you post a schematic for us? \$\endgroup\$ – Vladimir Cravero Feb 28 '16 at 18:32
  • \$\begingroup\$ Well, I'm 99% sure it is wired as in the datasheet. But as it is on a breadboard for evaluation purpose, I don't have any computer automated checking of the wiring. (It is the 1% left). I'll change the text to avoid confusion. I can send you a picture if you want but I'm not sure it is really readable \$\endgroup\$ – Julien Feb 28 '16 at 22:30
  • \$\begingroup\$ Your question is in the top 90 percent for this board. Add a schematic, snap a pic and you get to the top 99%... \$\endgroup\$ – Vladimir Cravero Feb 28 '16 at 22:38
  • \$\begingroup\$ Done. Did my best to make the breadboard understandable! ;) \$\endgroup\$ – Julien Feb 28 '16 at 23:13
  • \$\begingroup\$ I do not really have time right now, but your question looks great. I will hopefully have a look tomorrow. \$\endgroup\$ – Vladimir Cravero Feb 28 '16 at 23:22
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The answer is a bit stupid: le MOS was... dead. Lot of time lost.

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  • \$\begingroup\$ Such things happen. You have now learned to look for them sooner. \$\endgroup\$ – Asmyldof Apr 9 '16 at 11:50

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