Hi,
The series diode won't help.
The zener will do. But it adds capacitance ... and you need to care about impedance and speed.
But first you need to decide what is the peak operating voltage at this node?
I mean: you could use a free wheeling diode across the coil .... but this also limits the positive output voltage....and increases decay time.
I don't know what output voltage (waveform, polarity, timing ...) you want to use...thus I can't give a recommendation for now.
Klaus
An "avalanche rated" FET is one option. A FET whose BVdss
exceeds the flyback overshoot is another (and this is what will
maximize the output voltage; zener clamping or FET breakdown,
survivable or not, will clamp the primary hence the secondary).
NE555 is not that strong a driver and you may be seeing other
issues relating to weak drive.
Only true for DC currents..The 555 can output more current than the gate needs.
Hi,
Only true for DC currents..
Nowadays gate drivers can deliver >1A peak for fast switching.
Fast switching means low switching_loss and enables high switching frequency...
Klaus
No, switching speed at turnoff goes directly to how much
magnetizing energy is left in the inductor to produce the
flyback pulse, vs being scrubbed off by a leisurely drain
current transition. The slower the turnoff, the more switching
loss (the drain component, of; gate component is roughly
fixed Q per cycle, given constant Vgs(on)-Vgs(off)).
OP could interpose a vcvs between 555 block and FET gate
(av=1) and observe what (if any) impact there is to the
care-abouts. If it makes a difference then a gate driver
stage might be a win. Or, using a nearly-as-cheap PWM
IC which would also give you (if current mode controlled)
some authority beyond open loop volt-seconds over the
primary current.
Theoretically, yes. In practice, the ignition coil SRF (plus an connected external capacitor) sets a limit to current and respective voltage speed of change.No, switching speed at turnoff goes directly to how much magnetizing energy is left in the inductor to produce the flyback pulse
Is your ignition coil the same as found in an automobile? Car repair manuals tell how to test a coil's DC resistance with an ohmmeter, and what range of readings indicates a normal or faulty winding.
Remember that an inductor/transformer can generate high voltage spikes when you apply current and then suddenly remove it. So look for special instructions about taking ohm readings.
I recently ordered an LCR meter and an ignition coil
**broken link removed**
I dontt know what what values to input for parallel resistance for each winding.
These 2 specific values are apparently extremely important to obtaining a valid simulation output - and I am trying to achieve a voltage under the RMS AC capacitor voltage rating.
The item description at eBay gives 0.310 ohms resistance on primary and 9.2k ohms on secondary winding.
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