Rubens,
maybe you just need more current to drive the FET gates? A small
driver circuit, like an NPN or something, could probably help with
that. I don't know if it might even be enough to have caps there to
offset the current draw of the gate capacitance on turn-on, but it
might be worth considering for the simplicity.
Cheers,
- Marcel

On 3/10/07, rlistas <rlistas@gmail.com> wrote:
> Hi;
>
> I need some advices about noise in DC-DC Buck converters
> controler by a PWM generated with a PIC 16F88. Any help
> or ideas will be great.
>
> The buck circuit is capable of 2KW power output, using
> 4 power mosfets in parallel. It accepts a voltage in
> from 50 to 300V and output 50V.
>
> The problem is that with about 500W output
> the generate electrical noise resets the PIC
> or corrupt the data in the LCD displays that
> show the voltage in and power output.
>
> Observing the signal at the gate of the mosfets,
> the is a small spike in the turn on fase of the PWM
> that increases with power until the circuit resets.
>
> The gate of each mosfet is protected by a 15V zener,
> a series 33ohms resistor and a pull down 10kohms resistor.
>
> The driver circuit is a TC4420 and an 6N135 opto.
>
> The PIC circuit has decoupling capacitors of 100Uf and 100nf
> very near de power pins.
>
> All the cables from pic to power circuit are coaxial with only one side of
> the coaxial connectec to gnd.
>
> The buck inductor is a closed "E" type with gap, 100uh.
>
> I try LC filters in the PIC power lines, but didn=B4t work.
>
> The PIC circuit is about 10cm far for the power circuit.
>
>
> Thanks very much for the attention,
>
>
> Rubens
>
>
>
>
>
>
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