Using ECCP for Half Bridge PWM

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Rajan77
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2012/02/09 04:44:36 (permalink)
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Using ECCP for Half Bridge PWM

Hi everybody
       My attempt is to use ECCP in Half Bride PWM mode and construct a dc dc convertor. It works but when I changed Programmable dead band delay (changing PWM1CON value) in order to vary pulse width for output voltage correction, more heat produced in MOSFETs. Is this is a software or hardware issue? While checking outputs from PIC after disconnecting from switching devices, the wave forms seems ok. Any ideas ?? Thank you!!  
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    Ian.M
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    Re:Using ECCP for Half Bridge PWM 2012/02/09 08:46:05 (permalink)
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    Possibly insufficient gate drive?
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    Rajan77
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    Re:Using ECCP for Half Bridge PWM 2012/02/09 22:10:42 (permalink)
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    Ian.M,
             Thank you for taking interest in this case. No chance for insufficient gate drive because the circuit works well in normal heat when I worked it without voltage error correction and applying maximum pulse width (50 % in Half Bridge) with only 4us fixed dead band delay.
    The over heat generates only when I change dead band delay at run time.
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    Ian.M
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    Re:Using ECCP for Half Bridge PWM 2012/02/10 03:05:55 (permalink)
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    Well if you want a serious second opinion on your project, you will need to post a schematic, datasheet links for all non-Microchip active devices, specifications for the transformer, and attach your code.

    I suggest you also post pictures of the waveforms on both PWM outputs (2 channels on the scope):
    1. normal operation with fixed dead band
    2. PIC on its own with variable dead band
    3. variable deadband when driving the MOSFETS - you may need a LARGE resistor in the drain circuit to reduce the dissipation to a survivable level for the MOSFETS

    If you post photos here, you *WILL* need to use either IrfanView with its integrated RIOT plugin to save JPEGs with the file size set to 199K or your preferred professional graphics package to do the same.  It helps if you crop the edges of the image as much as you can.  There isn't a lot of point in trying to post an image over 1000 px wide here so you may want to resize the image to that width BEFORE using the RIOT plugin.
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