Hi,
I've made an audio amplifier that pops 1 or 2 seconds after power off, probably due to DC off-set or something like that. Now I want to make a MOSFET solid state relay based on this article by Rod Elliott, specifically the version with a transformer in it.
He suggests using a 500 μH inductance. I don't understand the importance of that other than that it should be too high or it will have a high impedance at high frequencies. Anyway, I tried to do the numbers and came up with the following, hoping to get away with 14 * 7 * 5 mm ferrite toroids because they're cheap and small:
outer diameter: 14 mm
inner diameter: 7 mm
height: 5 mm
relative inductance: 200 (assumption)
square wave frequency: 100 kHz at 15 Volts peak to peak
primary turns: 20, maybe 21 of AWG25
turn ratio: 1:1
ΔB = E / (4 * n1 * A_c * frq) = 0.1 T (I read somewhere[1] that 0.1 T is typical for ferrite)
L = μ * window_area * n1**2 / magnetic_path_length = 60 μH
Do you think this would work to drive a MOSFET? How do you calculate how much current it can handle?
About the relay, it has "clamping diodes" D4 and D5 that seem to do nothing. Is it that fast switching of the relay might cause high voltage spikes and that the diodes clamp it to either rail voltage?
[1] http://ecee.colorado.edu/copec/book/slides/Ch15slides.pdf
I've made an audio amplifier that pops 1 or 2 seconds after power off, probably due to DC off-set or something like that. Now I want to make a MOSFET solid state relay based on this article by Rod Elliott, specifically the version with a transformer in it.
He suggests using a 500 μH inductance. I don't understand the importance of that other than that it should be too high or it will have a high impedance at high frequencies. Anyway, I tried to do the numbers and came up with the following, hoping to get away with 14 * 7 * 5 mm ferrite toroids because they're cheap and small:
outer diameter: 14 mm
inner diameter: 7 mm
height: 5 mm
relative inductance: 200 (assumption)
square wave frequency: 100 kHz at 15 Volts peak to peak
primary turns: 20, maybe 21 of AWG25
turn ratio: 1:1
ΔB = E / (4 * n1 * A_c * frq) = 0.1 T (I read somewhere[1] that 0.1 T is typical for ferrite)
L = μ * window_area * n1**2 / magnetic_path_length = 60 μH
Do you think this would work to drive a MOSFET? How do you calculate how much current it can handle?
About the relay, it has "clamping diodes" D4 and D5 that seem to do nothing. Is it that fast switching of the relay might cause high voltage spikes and that the diodes clamp it to either rail voltage?
[1] http://ecee.colorado.edu/copec/book/slides/Ch15slides.pdf
Attachments
-
68.8 KB Views: 15
-
19.7 KB Views: 21