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Old 28th February 2010, 11:06 AM   #1
moro696 is offline moro696  Romania
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Default Chosing the right power for auxiliary supply

Hi all, since last summer i`m working on designing a power supply in full bridge topology using IGBT`s.
The problem i came up to is how mutch power i need from the auxiliary power supply to drive on the +15V rail necesary for the drivers of the igbt's
I intend to make the folowing circuit order Optoisolation - IR2113 -> TC4420
I want to use IRG4PC40W for the 4 pices of the bridge
Now from the datasheet of TC4420 i see it's maximum curent peak rating is 6Amps, my question is since in full bridge only two of the H bridge conduct, these would mean a total peak of let's say 12A peak?
Regarding my question, what rms current i must design the auxiliary power supply since it must carry out somewhere at 12Amps peak?
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Old 1st March 2010, 04:29 PM   #2
moro696 is offline moro696  Romania
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Nothing no one?
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Old 1st March 2010, 04:32 PM   #3
iko is offline iko  Canada
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The week-end can be slow at times, don't lose your patience. A schematic might help too.
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Old 2nd March 2010, 05:02 AM   #4
Eva is offline Eva  Spain
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If you are making that question, you are far from ready for starting such a project.

First learn how gate drive works in switching applications, you should know in detail what gate voltage and current waveforms look like.

Yes, required peak gate current may reach 6A or more in order to get fast switching from heavy MOSFET with big dies. With IGBTs there is no advantage past a certain point. But:
How long are those bursts of up to 6A going to last?
How many bursts are going to be required in one second?

Learn to interpret gate charge figures (Qg) on IGBT and MOSFET datasheets and you will be able to do rough calculations of the power used in gate drive.
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Last edited by Eva; 2nd March 2010 at 05:08 AM.
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Old 5th March 2010, 09:41 PM   #5
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Qg-tot times gate supply voltage is the energy needed to charge the gate.
You must supply this energy twice per period.
Half of the energy is lost as in every switched capacitor circuit.
So the total power consumption can be approximated by:
P=2*1/2*Qgtot*V*f
For a 100nC gate charge transistor driven to +15V at 10kHz it is rougthly 15mW.
Possibly the idle power consumption of drivers is of similar order.
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