Simulation of a blinking circuit (falstad)

[maelh]

Hello,

I have built a circuit from an electronics kit, which works as expected (blinking an LED).

But the falstad simulation of it, does not go into blinking mode. It lights up once, switches off, then gets "stuck".


The manual has the circuit (which uses one center-tapped coil of the transformer, but not the other one -- so essentially it just uses two independent coils):
https://www.robotshop.com/media/files/pdf/elenco-pk-101-manual.pdf (experiment #28, page 43).

I am not sure what I could change to make it work. Any ideas?

[Ian.M]

Two coils do not equal a Transformer, as the simulator doesn't know about the magnetic coupling between them.  Try [this] version.  It errors out after a few cycles but at least it oscillates.

Falstad *sucks* for this compared to a real SPICE simulator running on your PC/Mac.  The only thing going for it is its pretty animations!   I strongly recommend learning how to use the free LTspice SPICE simulator.   Its .asc simulation files are commonly used to share circuit ideas here and by other electronics communities.

[maelh]

If you look at the schematic in the PDF, the secondary side of the transformer remains unconnected.

The first simulation does oscillate, too, but it doesn't light the LED anymore.

[Ian.M]

What's the DC resistance of the transformer primary?  Falstad *may* be better behaved if you add resistors in series with the transformer windings to match. 

However, the operation of a Blocking oscillator is largely dependant on the transformer's core saturation characteristics, so Falstad is unlikely to give you realistic results.  LTspice doesn't directly support saturating coupled inductors, but you can put a saturating inductor (Chan model inductor core) in parallel with one of the coupled inductors to achieve the same effect.

[maelh]

Thanks, knowing it's a blocking oscillator helps already a lot. I'll read and report back.