sci.physics.electromag

On 25 feb, 12:54, Efthimios wrote:
> As you all know when AC pass threw a diode only halph the signal pass
> threw.
>
> But when I connect the diode to a coil the signal gets crazy. It looks
> like that the diode does not work. Between each AC peak an attenuating
> sinusoidal wave can be observed in the oscilloscope of grater
> frequency than my signal.
>
> Does any of you know to get rid of this attenuated sinusoidal wave
> form?
> I want to have a clear half AC wave form, as it should appear from the
> diode.
>
> Brgds

Hello,

The reason for that is that a diode has capacitance and it is not an
ideal switch. When the voltage across the diode goes from forward
voltage to reverse voltage, the diode doesn't "open" directly, so a
certain reverse current flows through the diode and your coil (search
for "reverse recovery time", or look into a diode datasheet). When the
diode opens, it shows a capacitance (same capacitance as in a varactor
diode) that makes the resonant circuit together with the inductor.

The current that flows through the coil just before the diode "opens"
provides the energy (I^2*L) for the starving resonance (Omega = 1/
sqrt(L*Cdiode). The circuit for damping this oscillation is called a
"snubber". Many times it is a combination of a resistor and a
capacitor across the diode or load.

You may post this question also in sci.electronics.design.

Best regards,

Wim
PA3DJS
www.tetech.nl