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Comment 11 ... 20
| date | article | author | comment |
| 17 okt 2021 09:21:05 | Additive synthese waveform generator | antonio | very well!!! how to add other presettings for flute, viola, ...? thanks! |
| 03 sep 2021 14:19:49 | Average & effective values | Freddy | Sorry, I completely overlooked the additional text in the sub chapter. The mistake is corrected. Thanks! |
| 02 sep 2021 23:19:12 | Average & effective values | Paul van Os | Just wanted to point out a typo *2/π instead of *π/2 |
| 01 sep 2021 23:58:57 | Average & effective values | Freddy | 0 (zero) is the only correct value. You can check this for yourself: Measure the AC mains voltage with a multimeter placed in the DC-range . The DC-range will measure the average value. Set the multimeters voltage range manualy so it fits the peak value of the mains voltage. This to avoid damage and unsteady automatic range switching. Now you will see the multimeter measures 0 volt. The value you're referring to is the average of the absolute momentarily values of a sine wave. This is mentioned in the examples above under "Full-wave rectification sine". |
| 30 aug 2021 00:01:39 | Average & effective values | Paul van Os | Could there be a small mistake in this part: "Average value sine wave The average value of a sine-shaped voltage or current is 0. But, often in literature, the value vpk*π/2 (≈0,637*vpk) is used." should read: (...), the value vpk*2/π (≈0,637*vpk) is used." |
| 22 jul 2021 20:53:18 | Extreme low voltage oscillator | Guy | A small update on my side: I tested roughly the same circuit but replaced the transformer with two 0805 size inductors with values of 180uH, and only used one JFET with Vgs at cutoff about 3V. It works and oscillates at up to 1.5MHz with a 22pF gate capacitor and I can adjust the frequency by replacing the capacitor or inductor. However, the circuit draws about 5mA and I wanted to lower the current. For that I will need to source higher value inductors and try again. It's quite reasonable when you think of it, when the JFET is open there is a straight path to ground through the inductor equivalent to the 'N2' winding. Also, I found that increasing the 'N1' inductance reduces the minimum supply needed for oscillation but does not reduce the overall current draw of the circuit. This proves that you really don't have to have the coupling of the windings in the transformer, discrete inductors work well. I like this inspiring small circuit. Guy Shemesh - ePiccolo Engineering |
| 11 jul 2021 19:26:36 | Magnetic circuits | Freddy | Not only the amount of energy that can be stored changes by applying an air gap: Also the magnetic resistance of the magnetic circuit increases, and with that the inductance decreases. And the product of the number of turns and saturation current increases. There is a lot going on with an air gap! |
| 11 jul 2021 15:34:16 | Magnetic circuits | Guy | Alright Freddy I accept your explanation. So this basically shows the potential in the air gap! essentially you localize the flux with the core and then force it through the air gap, at least for that small volume you have a very high energy store. Very interesting |
| 11 jul 2021 14:41:38 | Magnetic circuits | Freddy | @Guy, you are right if the field strength H where constant in every section of the magnetic circuit, but it is not. On the other hand, the flux density B is constant with some minor variations. These variation are caused by irregularities in the cross sectional areas. Especially the cross section of the airgap is affected by this. But as long the air gap length is much smaller than the width it's safe to assume an equal flux densitie in the whole circuit. |
| 11 jul 2021 14:12:18 | Magnetic circuits | Guy | Freddy, you wrote that the energy stored per volume in a magnetic field is calculated as: w = 0.5 * B^2 / μ. However, B conceals another μ, you could equally have written w = 0.5 * μ * H^2. And now the opposite is true, the higher the μ, the higher the stored energy. I need to refresh my physics studies but as far as I remember, H is invariant when crossing material boundaries while B by its definition is affected. |