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Do you know what type of LLC converter this is?

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We have had a 3kw offline (85-265VAC) battery charger made for us by a consultancy. They did not give us the schematic. The chargers are failing and we are wondering why. First of all we are trying to assess what topology it is.
The schematic that we have determined so far, by using the DMM on the PCB is as in the pdf. However, when we simulate this in LTspice , it doesn’t give as much output voltage as we see in the actual circuit on the bench. We are wondering if we have got the position of L7 correct?
We are running it into a 28 Ohm load and have set it to 250V output voltage. It is delivering obviously 8.9A into the load.
Do you know if there is some version of an LLC resonant converter that can give high gain so as to give the output voltage that we are seeing? By designing our own LLC resonant converter we find it is not possible to achieve 250V across a 28 Ohm load from a 415VDC input voltage. –But that is the output voltage that we are seeing on the bench with the circuit that they designed for us.
As such, do you know if there is a “type” of LLC resonant converter that can achieve what we are seeing here on the bench? I am not too sure if I have the power stage schematic exactly right.The switching frequency is definitely 100KHz, and the resonant frequency of L1 and C4//C1 is 110KHz, so it seems as if that is the resonant inductor and capacitance respectively.



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Would not the consultancy that designed the charger know their product best? If it is failing why not ask them to stand behind their design and make good on it or advise their thoughts on issues. Just a thought.


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I have made these.
Mine ran very cool. No heatsinks. No failures.
I put small caps across the MOSFETs that slowed the rise time a little.


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if we ask them for advice we have to pay.
It looks like I used a fet model with too high rdson in the above.


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Thanks, I think it is an unusual LLC design they have done for us...such a small external "resonant inductor" value that they have used. -And the addition of an extra inductor across the primary....this is to increase the magnetising current , and is presumably because of the output voltage range which is from 150V to 300V.
Also, the boss just told me that the transformer is not as in the above, he has now told me that the transformer is LP = 650uH, and NP/NS = 0.9.

Sorry about that, he actually gave me the transformer to measure, and then told me it was the wrong one.

I have reservations about an LLC resonant converter with vin = 415VDC and vout = 150v to 300v, as LLC's don't really like wide vout ranges...its hard to get soft switching over an entire wide range.


Well-Known Member
Thanks, do you think LLC converter is good for wide output range....eg
Vin = 390VDC
Pout = 3kW
Vout = 150 - 300VDC

Can the primary FETs be made to zero voltage switch on both transitions (turn on and turn off) throughout that whole load voltage range?
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