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Strange problem when simulate the boost converter?

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collin

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When i was simulating the boost converter,i found the power dissipation on the switch mosfet sometimes was bigger than the power source,and sometimes approximated to the power of power source,then the total power dissipation in the converter components was bigger than the power supply ,so where does this power come from? Is my simulation method wrong? this confused me very much ,so can anyone help me ? thank you!!

I think this large dissipation power is concernd to the reverse recovery current of the Schtokky diode,for i found just at the swithch transition time,Vds of the power mos is more than 30v(for the vout of the boost converter is 30v),and the reverse recovery current that flows through the powermos approximates to 1A. So this power dissipation is very large.

Notes: all the power was in rms,and the simulation tool was hspice.
 

collin said:
When i was simulating the boost converter,i found the power dissipation on the switch mosfet sometimes was bigger than the power source,and sometimes approximated to the power of power source,then the total power dissipation in the converter components was bigger than the power supply ,so where does this power come from? Is my simulation method wrong? this confused me very much ,so can anyone help me ? thank you!!

I think this large dissipation power is concernd to the reverse recovery current of the Schtokky diode,for i found just at the swithch transition time,Vds of the power mos is more than 30v(for the vout of the boost converter is 30v),and the reverse recovery current that flows through the powermos approximates to 1A. So this power dissipation is very large.

Notes: all the power was in rms,and the simulation tool was hspice.
Click to expand...

Remember, power is energy per second. The 1A current flow through a MOSFET with 30V vds only appear in a short time, so the energy is small, and the averaged power is small too.

Scottie
 

first,thank you for your replay.yes,the duration time of this spike is very short,but it have a significant impact on the dissipation power,to prove this you can see page811 of: fundmental of power electronics(second edition),i think it can increase the power dissipation many time.
 

collin said:
first,thank you for your replay.yes,the duration time of this spike is very short,but it have a significant impact on the dissipation power,to prove this you can see page811 of: fundmental of power electronics(second edition),i think it can increase the power dissipation many time.
Click to expand...

I agree with you that the shoot-through current (from output through the diode and the NMOSFET to ground) at the time that the NMOS is switched from OFF to ON causes a great problem in power efficiency of the entire boost converter. However, the efficiency of the converter cannot be larger than ONE, that is the message I would like to give in my previous response.

AS a reminder again, to access the efficiency of a switching power converter, averaged power is normally used.

Scottie
 

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