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I designed a buck converter on breadboard as shown in the picture. I am applying PWM from my microcontroller. I am not sure why this circuit is not working, I have spent so much time on it. Is there any problem with the connections? Or have I picked the right MOSFET and MOSFET driver? The MOSFET is N-type and the MOSFET driver is low- and high-side compatible. How do I know if the MOSFET driver is working as high-side or low-side? I guess PWM input from microcontroller is not a problem as I have tested it with a signal generator also.

buck converter


MAX627 data sheet**

enter image description here

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  • \$\begingroup\$ What are the input/output voltages and currents? switching frequency? Where is the feedback voltage signal? What is not actually working? \$\endgroup\$
    – KyranF
    Mar 31, 2015 at 23:08
  • \$\begingroup\$ Looks to me like your inductor is too big, capacitor is too small, and you arent even using a Schottky type diode? \$\endgroup\$
    – KyranF
    Mar 31, 2015 at 23:10
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    \$\begingroup\$ also looks like you were meant to do a P channel MOSFET not an N channel \$\endgroup\$
    – KyranF
    Mar 31, 2015 at 23:10
  • \$\begingroup\$ @KyranF input voltage is 15V and i am getting nothing as output. The switching frequency is 100Khz. I am not using any feed back voltage signal yet. I calculated the inductor and capacitor through calculations.The diode is Schotty type. \$\endgroup\$ Mar 31, 2015 at 23:27
  • \$\begingroup\$ Well i'm just telling you now, the values are wrong or you made a typo. Also, to switch the FET the gate needs 15V + at least Vgs(th) in the NFET datasheet, to turn on. Right now it's never turning on. How can you expect to control the conversion process without feedback? Buck converters require closed loop control. \$\endgroup\$
    – KyranF
    Mar 31, 2015 at 23:32

1 Answer 1

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I think, that's not the right kind of MOSFET and driver. In the present design, you've got an N-channel MOSFET and a driver MAX627. You are saying that it's "high side compatible". But there is nothing in a datasheet that indicates that that driver is for for a high-side N-channel MOSFET.

Combinations that should work:

  • Keep the driver that you currently have, but use a P-channel MOSFET.
  • Keep the N-channel MOSFET, but use some high-side gate driving technique (bootstrap gate driver, perhaps).
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  • \$\begingroup\$ Agreed, looks like a high-side circuit topology but using an N-FET. Need some charge-pump goodness to get above the 15V and turn that sucker on! \$\endgroup\$
    – KyranF
    Mar 31, 2015 at 23:21
  • \$\begingroup\$ Yes, the MAX627 is just a low side driver. A P channel could be used with it but only because the input is 15V, much higher an driver and FET gate would be damaged. \$\endgroup\$
    – gsills
    Mar 31, 2015 at 23:23
  • \$\begingroup\$ MAX627 is high and low side driver. Its mentioned in RS components specifications when buying it. \$\endgroup\$ Mar 31, 2015 at 23:28
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    \$\begingroup\$ @SamadMuhammad There is a big difference in High-side P-channel drive and High-side N-channel drive. They are both high side, but driving them is completely different. It sounds like it's a high-p / low-n driver, not a high-n / low-n driver. \$\endgroup\$
    – Majenko
    Mar 31, 2015 at 23:38
  • \$\begingroup\$ @Majenko so do you think that using ptype mosfet with same driver will work out? \$\endgroup\$ Mar 31, 2015 at 23:43

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