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L6491EVAL has excessive switching loss

Question asked by Richard Tarbell on Dec 27, 2016
Latest reply on Jan 20, 2017 by Fabbri.Fabio

Project: Make one full bridge (non-isolated) rectifier, using two L6491EVAL boards as the gate drivers (the switching transistors mounted to them are FCH190N65F).  

 

full_bridge_schematic

 

Initial testing approach: test the full bridge rectifier circuit as a DC-DC converter (just to verify functionality) by applying 10VDC to the input, vary the PWM duty cycle to each gate driver board, and then measure the output voltage (it should increase as the duty cycle increases).  Just for safety/sanity, my 10VDC input source is current limited to 1 amp, and there is no load on the output of the full bridge.  

 

Problem: With Vin=10VDC, and starting at a PWM of 0%, I get an output of 10VDC (expected), and almost no losses.  However, as I increase the PWM, my current draw on the source supply increases pretty steeply:

 

PWM %      Input supply current:        Vout

5                    0.06 A                                 11.0

10                  0.20                                   12.3

15                  0.41                                   13.85

20                  0.58                                    14.8

25                 Supply current limit at 1.0A

 

--> It seems that my current draw is WAY too high for "normal" operation.  I suspect that Any ideas as to what I should be looking for?  The L6491EVAL boards do have a dead-time potentiometer, but adjusting these seem to do nothing.  Are there any other adjustments I can make, to reduce the power losses?

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