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durgarao
Level 1
Level 1
5 replies posted 5 sign-ins First like given

Hi,

  IPT60R145CFD7XTMA1 Mosfet used for half-bridge converter, it is working fine. But datasheet is not recommending CFD7 for hard-switching applications. Why CFD7 can't be used in Hard-switching & what specification of the mosfet preventing it using in hard-switching applications.

 

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1 Solution
Neo_Qin
Moderator
Moderator
Moderator
250 replies posted 250 sign-ins 100 solutions authored

Hi @durgarao ,

Switching time parameters listed in the table section of the datasheet are obtained under specific conditions, a direct comparison is not a reasonable act, and the real-life waveforms do not necessary look alike due to different application conditions. 

Neo_Qin_0-1680865128646.png

In fact, a better representation of the MOSFET switching speed is gate charge diagram, which illustrate as below (take IPB60R040CFD7 as example):

 

Neo_Qin_2-1680865679096.png

In a typical flyback hard-switching topology circuit, EMI interference levels are influenced by a combination of MOSFET characteristics and peripheral circuit parameters/PCB layout. 

In reality, MOSFET on/off transients are generally reduced by adjusting the gate drive network, and  an RCD clamp circuit added to suppress voltage spikes. Careful consideration should be performed to achieve the best trade-off between minimizing switching losses, avoiding induced turn-on (if applicable) and controlling EMI emissions.

Neo_Qin_3-1680867432569.png

In short, a good design always has a balance of performance. And Infineon offers power MOSFET products optimized for various topology applications, simple to follow guidelines that can save you a lot of time.

Neo_Qin_4-1680867945827.png

Kind Regards,

Neo

View solution in original post

9 Replies
喜马拉雅之雪
Employee

For CFD7 MOSFET, they are OK for hard-switching. The "problem" is only "not best".

CFD7 is focus on development bode diode(Trr / Qrr) and Qg performance for best meet ZVS (LLC...) application.

Standard MOSFET is focus on RDSON and Qg with best switching and "ON" power loss.

So they have different road mape with best for different application.

Thanks for the reply,

Then if Rdson & Qg are acceptable for the application means i can use the CFD7?

I verified C7,P7,G7 with CFD7, i found the only difference in Turn-on delay time,Rise time,Turn-off delay time,Fall time  are better compared to CFD7 & trr and Qrr is poor in C7,P7,G7.

Then Switching losses in C7,P7,G7 series will be less than CFD7 series mosfet. So obviously C7,P7,G7 are better for hard-switching where hard commutation is not required.

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👍Yes!

Standard MOSFET is focus on switching and "ON" power lose. So fast switching and low EMI noise are important for easy use and remove hardswitching loss.

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Fast switching means fast turn and turn off i.e fast switching will result in high dv/dt and high di/dt. High dv/dt and di/dt will increase the EMI noise. How device will help in achieving fast switching and low EMI?

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Yes,dv/dt & di/dt are important for EMI on rotine. But this is not only.

For example, Coss...

So EMI is from MOSFET best performance and not only switching speed.

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Neo_Qin
Moderator
Moderator
Moderator
250 replies posted 250 sign-ins 100 solutions authored

Hi @durgarao ,

As a general rule, it is important to choose the right type of power MOSFET for a particular design based on the type of switching that takes place.

In a typical QR circuit as shown below, assuming that the rated parameters of the device are not abused, COOLMOS CFD7 (with fast body diode) can certainly be applied in this field of hard-switching topology, and a smaller switching off overlap be expected. However, fast changing di/dt or dv/dt causes worse EMI issues. In other words, after balancing EMI issues and energy losses, CFD7 is not the best choice in this application scenario.

Neo_Qin_1-1680851315421.png

But in various soft-switching topologies, things have changed. Most resonant circuits are half- or full-bridge topologies (2 or 4 MOSFETs). As MOSFETs are switched on and off, energy can be left in the MOSFET and this can cause failure. Due to switching times if this only happens occasionally,  a rugged body diode is sufficient (CoolMOS P7). If due to fast transition times it happens continually then a fast body diode is required to make sure all the energy will leave the MOSFET (CoolMOS CFD7 Series).
 
Different MOSFET technologies have different degrees of body diode ruggedness and different reverse recovery speeds. It is important to select devices that are suited to applications.
 
For more details, please refer to the following URL:
Kind Regards,
Neo

Hi Neo_Qin,

   P7 series Turn-on delay time,Rise time,Turn-off delay time,Fall time are better compared to CFD7, so P7 will switch faster than CFD7 for hard-switching. If so P7 series should generate more EMI problems compared to CFD7?

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Neo_Qin
Moderator
Moderator
Moderator
250 replies posted 250 sign-ins 100 solutions authored

Hi @durgarao ,

Switching time parameters listed in the table section of the datasheet are obtained under specific conditions, a direct comparison is not a reasonable act, and the real-life waveforms do not necessary look alike due to different application conditions. 

Neo_Qin_0-1680865128646.png

In fact, a better representation of the MOSFET switching speed is gate charge diagram, which illustrate as below (take IPB60R040CFD7 as example):

 

Neo_Qin_2-1680865679096.png

In a typical flyback hard-switching topology circuit, EMI interference levels are influenced by a combination of MOSFET characteristics and peripheral circuit parameters/PCB layout. 

In reality, MOSFET on/off transients are generally reduced by adjusting the gate drive network, and  an RCD clamp circuit added to suppress voltage spikes. Careful consideration should be performed to achieve the best trade-off between minimizing switching losses, avoiding induced turn-on (if applicable) and controlling EMI emissions.

Neo_Qin_3-1680867432569.png

In short, a good design always has a balance of performance. And Infineon offers power MOSFET products optimized for various topology applications, simple to follow guidelines that can save you a lot of time.

Neo_Qin_4-1680867945827.png

Kind Regards,

Neo

Thank you Neo_Qin

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