Hello all,
I'm designing an unregulated power supply filter and trying to make sense of my calculations.
Obviously, the goal is to minimize 120Hz ripple after rectification. Some use a single capacitor, some an RC, some a CRC... etc.
I've put together a 3-pole filter (CLC) and have worked out the transfer function. Source and load resistances are considered. The eqn and a magnitude response graph is attached, but the real takeaway is that I should be seeing about 5dB of attenuation at 120 Hz.
The CLC schematic is attached. This is simulated in SPICE. When the input is a non-rectified 70Vpp sinusoid, I indeed see 5dB of attenuation.
What I'd like help making sense of is the filter output when the input is a rectified sine wave. As would be expected, there is a significant DC component with a ripple riding on top. The peak to peak ripple voltage is almost 4 volts. An image is attached.
I have no way of explaining this mathematically. The ripple seems to have gone from 35Vpp to 4Vpp, which is nearly 19dB of attenuation. Clearly, my 5dB figure no longer applies. I suspect that the disparity has something to do with me ignoring the resulting DC component when the input is rectified.
Is there any shorthand way to calculate the ripple output of this filter like I would with a non-rectified sine wave? The only recourse I can think of would be to find the output in the s-domain and take an inverse laplace transform... this gets disgusting.
Thanks for any help!
I'm designing an unregulated power supply filter and trying to make sense of my calculations.
Obviously, the goal is to minimize 120Hz ripple after rectification. Some use a single capacitor, some an RC, some a CRC... etc.
I've put together a 3-pole filter (CLC) and have worked out the transfer function. Source and load resistances are considered. The eqn and a magnitude response graph is attached, but the real takeaway is that I should be seeing about 5dB of attenuation at 120 Hz.
The CLC schematic is attached. This is simulated in SPICE. When the input is a non-rectified 70Vpp sinusoid, I indeed see 5dB of attenuation.
What I'd like help making sense of is the filter output when the input is a rectified sine wave. As would be expected, there is a significant DC component with a ripple riding on top. The peak to peak ripple voltage is almost 4 volts. An image is attached.
I have no way of explaining this mathematically. The ripple seems to have gone from 35Vpp to 4Vpp, which is nearly 19dB of attenuation. Clearly, my 5dB figure no longer applies. I suspect that the disparity has something to do with me ignoring the resulting DC component when the input is rectified.
Is there any shorthand way to calculate the ripple output of this filter like I would with a non-rectified sine wave? The only recourse I can think of would be to find the output in the s-domain and take an inverse laplace transform... this gets disgusting.
Thanks for any help!