conduction power loss of SiC diode

Thread Starter

orcuns91

Joined Nov 5, 2020
2
Hi everybody,
I'm trying to find the correct conduction loss value of a SiC Schottky diode. While the diode is in conduction, 33.5 A square wave current flows through it. I should use this current when determining the forward voltage in the forward characteristic graph in the datasheet, or is it 8.375 A, which is the average current value? You can also see the current waveform of the diode. (f=20 kHz, D=025) Thanks in advance.
 

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Delta prime

Joined Nov 15, 2019
838
To calculate maximum conduction losses, read maximum values of VF at IMin and IMax.
The first step is the calculation of the average and rms currents.
The forward average current is the output current: IF(AV) = Iload
The forward current has a trapezoidal shape." Please forgive me I don't know the
formula to calculate the rms current of trapezoidal waveform".:(
 

Papabravo

Joined Feb 24, 2006
15,521
To calculate maximum conduction losses, read maximum values of VF at IMin and IMax.
The first step is the calculation of the average and rms currents.
The forward average current is the output current: IF(AV) = Iload
The forward current has a trapezoidal shape." Please forgive me I don't know the
formula to calculate the rms current of trapezoidal waveform".:(
  1. Square the waveform
  2. Take the average of the squared waveforn (≡ area under the curve)
  3. Take square root of the average of the squared waveform
You can do it graphically as well
 

crutschow

Joined Mar 14, 2008
26,792
Since the diode forward drop is relatively constant, (not ohmic) you use the average value of the current, not RMS to calculate the diode power loss.
 

Papabravo

Joined Feb 24, 2006
15,521
Since the diode forward drop is relatively constant, (not ohmic) you use the average value of the current, not RMS to calculate the diode power loss.
I could not read the markings on the waveform scale. Does your average include the part where the diode is apparently(?) non-conducting?
 

Thread Starter

orcuns91

Joined Nov 5, 2020
2
Thank you for your answers. However, I still haven't been able to decide which Vf value to get. I increased the visibility of the current waveform and shared it in the attachment. Could you tell me what value should it get?

dd.pngddddd.png
 

Papabravo

Joined Feb 24, 2006
15,521
Is that a significant value of current in this configuration?
The graph of the current waveform is interesting in a pictorial sense, but I can't read any values, so I can't answer your question The original question revolved around a value for forward voltage when the diode was conducting. Which of the two values specified by the TS should be used, or is there another average value that you would prefer?
 

ronsimpson

Joined Oct 7, 2019
1,161
Power loss: I am using the 75C line because the silicon in side the diode will be hot.
Should be using calculus to find the area under the curve of V*A.
Power loss for the on time =((40A @ 2.6V)+(27A @ 2.0V))/2 Approx.
Another option is to average the 40A and 27A and also average the 2.6 and 2.0V. Two watts less than above.

Next is to use duty cycle or on_off time.
 
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