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I'm trying to simulate this circuit

enter image description here

This is the implementation

enter image description here

I'm getting this output signal, that is close to what you would expect from a rectifier. In this image α = 0, α1 = π/6, α2 = 5π/6 and α3 = 3π/2. The α is the turn on angle for the thyristors.

enter image description here

But there's a negative part that shouldn't exist, The same happens for bigger alpha, for example α = π/2 would result in this:

enter image description here

What would be the reason for this drop down in voltage ? The output signal should only have positive voltages.

What changes can be done to get a better output signal?

Is there something else I'm missing in the circuit?

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  • \$\begingroup\$ SE supports the use of HTML entities including all the Greek letters such as α and π (but they don't work in the comments). It also supports MathJAX so you can do \$ \alpha \frac {\pi} 6 \$. \$\endgroup\$
    – Transistor
    Jul 7, 2021 at 14:03
  • \$\begingroup\$ This question appears very similar to your previous two on the same topic. Can you explain the differences? \$\endgroup\$
    – Transistor
    Jul 7, 2021 at 14:05
  • \$\begingroup\$ In my first question I asked about the design of the isolation circuit. In my second question the subject was the behavior of the circuit resulting in a wrong signal according to the alfa turn on angle. In this one the output signal is close to what is expected for the given alfa, but now it has some sort of negative part that shouldn't be there. \$\endgroup\$
    – Samu R
    Jul 7, 2021 at 14:12
  • \$\begingroup\$ Seems that the duration pulse for triggering not enough ? Add the picture for pulses. 100 us min to 1 ms. \$\endgroup\$
    – Antonio51
    Jul 11, 2021 at 18:32

1 Answer 1

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The duration pulse for triggering is not enough. The thyristors do not go really in conduction, only an attempt to do. Note that in resistance load, angle is limited to 180°. Add the picture for pulses. 100 us min to 1 ms.

The picture would be ... in case of resistive load, case angle= 18° (1 ms @ 50 Hz).

enter image description here

In case of inductive load, a "guard" time must be set, so angle < (180°-guard angle), generally guard angle = 30°, angle limited to 150°.

Here, picture for time = 7ms -> angle = 7* 18° = 126°.

enter image description here

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