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Measure temperature and power losses?

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mading2018

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I think it is better if you check my model, cause I am not sure what to change when it comes to coils and capacitors.
I skipped the capacitors and inductors since they can't be losses measured. I need to hand calculate those.

I want to find the temperature of all the components that are included in table that I have attached. You can also see the average power losses from LTspice.
 

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ronsimpson

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R3, R6 1M resistor:
Most small resistors will not survive 600 volts. You need to find a high voltage resistor. (or use resistors in series)
Next find the average voltage and current. watts. Choose a resistor that can withstand that power.
A 1W resistor with 1W of power will almost melt the solder.
I usually run resistors at 1/2 power to keep the temperature down.
(you must choose a real part before you can get the temperature)

D1,3,4,5:
Spend some time with the data sheet. It looks like the maximum temperature is hit at 1.1V @ 1A. So it is a 1.1 watt diode. Max temp 150C junction temperature.
Question to you; Is this the right part? Is your average current above 1A or below 1A?
 

mading2018

Member
But this those values for the resistors was standard value from the demo. Since this is a simulation, do I really need to find real parts?
I am not sure if I can find a high voltage resistor in LTspice or how large should the series resistors be.

Hmm, did you check the temperature? I may have selected the wrong parts, but I do not have how to select the correct ones i LTspice. The average current is higher than 1 A.
 

ronsimpson

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do I really need to find real parts?
No. SPICE does not make smoke or fire. You can put 600 volts on a 35 volt capacitor and nothing bad happens.

I think the exercise of picking a real resistor is much like picking the right diode.

In the case of your transistor, we need to know how much power, then pick a heat sink.
I used a R6020ANX which is 600V, 50watt transistor in a to-220 case. But 50 watts is with a infinite heat sink.
With no heat sink the temperature goes up by 70C/watt. (25C room temp, 1 watt=delta of 70C = 95C )
Probably you will need to pick a heat sink with a known thermal resistance.
 

mading2018

Member
Hmm, I am not able to find "R6020ANX " in my library. Is it not included maybe, is that transistor an external part? Yes, a heatsink is probably needed.

--edit--
the choice of the components in LTspice would effect the efficiency and losses right?
 
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ronsimpson

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I am not able to find "R6020ANX " in my library
And I can not find the R6020PNJ in real life.
The ANX/PNJ is the case style. The R6020 is the silicon.
Table of case styles that I can find:
ENZIC9 = TO-247
ENZIC8 = TO-3P
ANX = TO-220
KNJTLTR = TO-263
To know the temperature of a part you need to know how much power AND the thermal resistance. (how that power gets to the air)
Each case has a different resistance to air and a different resistance to a heat sink.
 
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