Here is the circuit we used (BT169 thyristor):
And this is the output:
In theory it should be a straight line when AC source goes negative.
The question is "Why does it go into the negative area? Why is it not a straight line?"
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.Sign up to join this community
From memory, the GK junction of an SCR, in reverse mode, acts as a Zener diode of 7V or so (much like the BE junction of a transistor). A current flows through RL, this GK zener diode, and R1, creating the voltage across RL observed. The zener thresold explains why there are two periods with almost no current during a cycle.
If that effect is undesirable, inserting a diode in series with R1 (cathode connected to G, anode to R1) should reduce it (but the SCR will turn on a little later).