...and please explain what the circuit is supposed to do.
It will always give strange results when you connect a small germanium diode across an inductor like that. All it can possibly do is trap back EMF but even then it may be exceeding it's ratings.
Is it only me the one that has noticed that the output is connected to the input?
What exactly are you attempting to do?
Also as Brian has noted, utilizing a Germanium small signal diode in a switchmode supply is wrong.
Hi,
Did you think about / calculate / measure the diode current?
Klaus
Hi,
Did you think about / calculate / measure the diode current?
Klaus
I'd remove the input to output connection, there is nothing normal or useful about it
This is not a switching supply. Redrawing the circuit like below, might help.Switching supplies, whatever name you may want to gild them with, have "spiky" outputs.
I think the problem is not the diode, but the decoupling. Add a 100 uF bulk cap and 100 nF decoupling very close to the inductor and also the whole layout very tight.
I think the problem is not the diode, but the decoupling. Add a 100 uF bulk cap and 100 nF decoupling very close to the inductor and also the whole layout very tight.
Inductance looks like the problem, often flyback and
boost converters need a snubber to shave off the
leading edge energy.
I'd remove the input to output connection, there is nothing normal or useful about it - choose one path (or the other), and then check what's happening.
Switching supplies, whatever name you may want to gild them with, have "spiky" outputs.
As a 30-minute experiment aside it might be interesting to make a discrete voltage doubler (or voltage inverter by reversing the diodes) - two diodes, two capacitors and a squarewave input, then zoom in on the output signal.
1) What is the ringing frequency after you added the decoupling parts ?
2) Does the ring still goes to 20 V as it did before, if you scope it for a long time ?
3) Show the image with the same zooming as in post #1 for better comparison.
Hi,
It helps to see the correct schematic drawing, thanks CataM. Yes, in comparison to linear. This is a close-up of simulated results of a discrete voltage inverter waveform, this one is quite neat compared to other ones I've messed around with.
View attachment 143738
I'm still puzzled by what you are trying to achieve. It seems your circuit has no output and all you are doing is pulsing current through the coil then wondering why it shows a damped oscillation. The diode is connected directly across the coil and with the exception of it's turn-on time just clamps one polarity. Also note that the absolute maximum VDS of that MOSFET is 12V which you are exceeding. The layout is probably responsible for the 23MHz ringing, mounting the MOSFET on a small PCB and running wires to it is asking for trouble.Which brings me back to the question; there is current galore (3A spikes) going through the diode, but the voltage remains on the other side, why?
Dick, by "snubber" do you mean Resistor-Capacitor-Diode (RCD) Snubber? If yes, it still has to go through a diode, so the problem would remain.
View attachment 143735
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