TINA/Spice: Question about buck DC-DC

Erogan

Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

I have put up a open loop buck circuit and use this circuit to do simulation. The input stimulus is 3V DC voltage and a 5V square wave with 40% duty to control the high side NMOS.

In theory, the output should be 3*40%=1.2V. But the simulation result show it is 3.28V. Could you tell me why? You can see my simulation report as attached. Thanks

tina simulation report_buck.docx

over 7 years ago

0 Erogan over 7 years ago

Prodigy 130 points

The simulation source file6102.buck.TSC

0 Karthik Kulkarni over 7 years ago in reply to Erogan

TI__Intellectual 1090 points

Hi Chen,

Couple of things to note in your schematic.

1. Output resistance is too high. There is no path for the capacitor to discharge as you are using a diode at lower side. Thus Vout keeps on increasing.

2. The source resistance of 50Ω is also high. You can use something in the range of few mΩ's.

3. The MOSFET chosen has a VT of 3.1V. The MOSFET does not turn on completely with a VIN of 5V. I would recommend use a MOSFET with 0.5V ~ 1V. If not, increase the Gate voltage so that it turns on completely(linear region).

Regards,

Karthik

0 Erogan over 7 years ago in reply to Karthik Kulkarni

Prodigy 130 points

Hi Karthik

Thanks a lot for your useful opinion. I have solved my problem now.

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TINA/Spice: Question about buck DC-DC