I'm designing a buck converter using the HV9918 IC to drive some high current LED's.
I'm seeing some huge spikes at high bandwidth in the current waveform. Does anyone know where they're coming from?
These waveforms are across a 1.7 ohm current sense resistor. So the current in amps is approximately 60% of whatever amplitude is shown in the pictures. The average current is about 250mA. I'm driving a 6.8V zener diode.
In all these pictures the bottom flat trace shows the 0V level for the top trace.
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The switching frequency is about 1MHz. There are huge spikes that are 700mA peak-to-peak!
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Zoomed in. Those sine waves are about 300MHz. My scope is a 2465B 400MHz and I'm using a 400MHz probe measuring across the sense resistor with the ground lead.
**broken link removed**
With bandwidth limit of 20MHz on the scope, the current ripple looks much more reasonable. Only 30mA ish.
Is it coming from the wiring inductance? I have the zener diode and external current sense resistor (not the internal sense resistor for the buck converter) connected using alligator clips to each other. But my main intent is to have the LED's connected with a cable.
Should I even worry about it? Will the LED's "see" this high frequency current spike if a 20MHz scope doesn't?
I'm seeing some huge spikes at high bandwidth in the current waveform. Does anyone know where they're coming from?
These waveforms are across a 1.7 ohm current sense resistor. So the current in amps is approximately 60% of whatever amplitude is shown in the pictures. The average current is about 250mA. I'm driving a 6.8V zener diode.
In all these pictures the bottom flat trace shows the 0V level for the top trace.
**broken link removed**
The switching frequency is about 1MHz. There are huge spikes that are 700mA peak-to-peak!
**broken link removed**
Zoomed in. Those sine waves are about 300MHz. My scope is a 2465B 400MHz and I'm using a 400MHz probe measuring across the sense resistor with the ground lead.
**broken link removed**
With bandwidth limit of 20MHz on the scope, the current ripple looks much more reasonable. Only 30mA ish.
Is it coming from the wiring inductance? I have the zener diode and external current sense resistor (not the internal sense resistor for the buck converter) connected using alligator clips to each other. But my main intent is to have the LED's connected with a cable.
Should I even worry about it? Will the LED's "see" this high frequency current spike if a 20MHz scope doesn't?