So today I am going to expand on my previous pi-filter topology to make it compatible with the solenoid driver. The same driver that is going to be dealing with ~7 Hz 10 A transients ;^)
Chosen Pi-Filter Configuration
As before, here is the step and frequency response of the chosen pi-filter configuration. Since I am dealing with a higher transient current, I am trying to minimize things like:
- Settling time
- Over/under-shoot
- Frequency of ringing (think radiated EMI)
If you are confused about some of the above terms then have a look at the next section
Summary of Ferrite Beads
With the previous lot of simulations I was quite happy with the electrolytic & ceramic capacitor arrangement (which turned out to be ideal for this case as well), so this time I dived deeper into the impacts of ferrite bead impedance
The step response was configured to peak at 10 A, which is the peak current of the solenoid I wound. As I began simulating stuff I noticed that such a large current spike lead to noticeable over/under-shoot & ringing, hence I evaluated each ferrite with this in mind
Rather than flood yous with pictures of different ferrite bead simulations, this time I decided to summarize the data in a nice table:
Note how the NO FILTER response:
- Has a rather "late" -3 dB roll-off frequency, ~3,500 kHz vs ~160 kHz for others
- Manages to amplify any transients in the ~30 kHz to ~3.2 MHz range
- Has a step response that oscillates at ~2.2 MHz (think radiated EMI)
At the same time, now how using a higher impedance ferrite bead (48-115 Ω @ 100 MHz) leads to:
- Amplification of any transients in the ~15 kHz to ~150 kHz range
- An increase in settling time
- An increase in over/under-shoot
In my opinion the 10 Ω @ 100 MHz ferrite bead (Wurth 74279221100) gives the best performance of the lot. With the most noticeable/worthy feature being no amplifiaction of transients from 1 Hz all the way to 100 GHz :D
Closer Look at 115 R Ferrite Bead
For the sake of completeness, here is how the largest impedance ferrite bead (Liard 28F0181-1SR-10, 115 Ω @ 100 MHz) looks
No comments:
Post a Comment