Is there anything wrong with the R+L measurement?
Monitor the voltages across the R & the L until you find the Frequency where the voltages match. At the matching voltage, the phase shift is 45° and the Frequency is the F-3dB.
Then use XL= 2PiLFwhich rearranged gives L= XL/2PiF (L in Henries for ohms and Hz)
Monitor the voltages across the R & the L until you find the Frequency where the voltages match. At the matching voltage, the phase shift is 45° and the Frequency is the F-3dB.
Then use XL= 2PiLFwhich rearranged gives L= XL/2PiF (L in Henries for ohms and Hz)
No Andrew there is nothing wrong, but like i said that's only one parameter i would like to set saturation currents cause most of the time times i don't have the core data and this is a nice setup to do a test fixture for those phantom core with strange colors and sizes...
This post shows current state of the tool/prototype.
Four improvements were made:
- Turn off speed up diode (1A schottky or 200V ultrafast) was added in parallel with 22r gate resistor.
- Two small ferrite beads were added in series with FET gate (total .5~1uH) to achieve semi-resonant turn off, skipping partially or completely "miller" period. This gets faster edges when using the circuit as "square wave dummy load" for finding resonances in supply rails.
- A 470r potentiometer was added in series with the 100r resistor that is used to add a pole (LPF) to cancel the zero introduced by .022r current sense resistor inductance (~30nH, ~1nH/mm of pad spacing). This forms a variable divider. The oscilloscope probe is connected to the divider (100r to pot junction) and the pot should be adjusted for coherence of edges of current sense waveform.
- In the capacitor of this LPF (4.7n) ground connection was moved from PCB to sense resistor directly for more accurate waveform and to make grounding 2 oscilloscope probes to the same location easier (alligator clip directly to capacitor).
In the pictures showing oscilloscope CH1 is 1:1 probe and CH2 is 100:1 probe.
Four improvements were made:
- Turn off speed up diode (1A schottky or 200V ultrafast) was added in parallel with 22r gate resistor.
- Two small ferrite beads were added in series with FET gate (total .5~1uH) to achieve semi-resonant turn off, skipping partially or completely "miller" period. This gets faster edges when using the circuit as "square wave dummy load" for finding resonances in supply rails.
- A 470r potentiometer was added in series with the 100r resistor that is used to add a pole (LPF) to cancel the zero introduced by .022r current sense resistor inductance (~30nH, ~1nH/mm of pad spacing). This forms a variable divider. The oscilloscope probe is connected to the divider (100r to pot junction) and the pot should be adjusted for coherence of edges of current sense waveform.
- In the capacitor of this LPF (4.7n) ground connection was moved from PCB to sense resistor directly for more accurate waveform and to make grounding 2 oscilloscope probes to the same location easier (alligator clip directly to capacitor).
In the pictures showing oscilloscope CH1 is 1:1 probe and CH2 is 100:1 probe.
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.