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Science Forum Index » Physics - Electromagnetic Forum » RL with Diode Circuit
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Message |
| Efthimios |
 Posted: Mon Feb 25, 2008 1:54 am |
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Guest
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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 |
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| Wimpie |
| Posted: Mon Feb 25, 2008 9:09 am |
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On 25 feb, 12:54, Efthimios <eangelopou...@gmail.com> wrote:
Quote: 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 |
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