This applet shows the effect of a free-wheeling diode connected to a thyristor (the configuration given here is more educational than practical). Without the free-wheeling diode, the thyristor must be triggered to go into the on-state. The current rises, and goes down to zero after the output voltage turns negative. With higher inductance the on-state duration is increased. If a free-wheeling diode is present, it will start conducting as soon as the output voltage turns negative. With the conducting diode, the output voltage is zero while output current is still flowing. The voltage drop on the resistance is offset by the voltage drop on the inductance. Input current, which is equal to the thyristor current, is cut off after the input voltage turns negative.

• Change the values of the resistor and inductor to influence the current waveform.
• Change the triggering angle to change the output voltage, especially its averaged value (not shown in the applet).
• Drag the time slider from left to right. After passing the triggering point, the trigger pulse is animated. After triggering, the thyristor is in the on-state and the load current keeps flowing.
• Activate and deactivate the free-wheeling diode by clicking its symbol in the circuit drawing.