Observations: Laboratory Exercise #21 We can see from this exercise that the primary function of a DIAC is to phase shift a TRIAC. I do not have the reading of the voltage drop across the DIAC but knowing how a DIAC works I can tell what would happen. I’m assuming that the DIAC we used was an IN5761. If so, the operating voltage would be 7 Volts and as long as the holding current (IH) does not go below what it is rated, the DIAC will continue to have 7 Volts dropped across it. When the applied AC voltage has been lowered with the autotransformer the voltage drop across the DIAC remains constant because of the characteristics of the diode. With the DIAC being an AC intrinsic thyristor it essentially acts like a zener diode for AC. However, it can conduct on either half of an AC waveform because it is bi-directional unlike a zener diode which is only used in the reverse biased configuration. Laboratory Exercise #23 Due to the triac essentially being two SCR’s connected in parallel with the gate leads tied together, the triac must be phase shifted to gain complete control of the AC wave. In order to phase shift the triac a diac is used to trigger the gate of the triac during positive and negative alternations of the AC waveform. The part of the circuit that controls the phase shifting is the resistors R1, R2, and capacitor C1. The size of R1 essentially determines the upper limit on the amount of charging current that can be delivered to the capacitor. With R2 being adjustable we can determine how long the charge time is for the capacitor and basically control when the triac is fired based on the characteristics of the diac. By adjusting R2 what we would basically see is similar to the phase shifting of an SCR. The light bulb would dim and go bright depending on when the triac was fired thus determining how
Observations: Laboratory Exercise #21 We can see from this exercise that the primary function of a DIAC is to phase shift a TRIAC. I do not have the reading of the voltage drop across the DIAC but knowing how a DIAC works I can tell what would happen. I’m assuming that the DIAC we used was an IN5761. If so, the operating voltage would be 7 Volts and as long as the holding current (IH) does not go below what it is rated, the DIAC will continue to have 7 Volts dropped across it. When the applied AC voltage has been lowered with the autotransformer the voltage drop across the DIAC remains constant because of the characteristics of the diode. With the DIAC being an AC intrinsic thyristor it essentially acts like a zener diode for AC. However, it can conduct on either half of an AC waveform because it is bi-directional unlike a zener diode which is only used in the reverse biased configuration. Laboratory Exercise #23 Due to the triac essentially being two SCR’s connected in parallel with the gate leads tied together, the triac must be phase shifted to gain complete control of the AC wave. In order to phase shift the triac a diac is used to trigger the gate of the triac during positive and negative alternations of the AC waveform. The part of the circuit that controls the phase shifting is the resistors R1, R2, and capacitor C1. The size of R1 essentially determines the upper limit on the amount of charging current that can be delivered to the capacitor. With R2 being adjustable we can determine how long the charge time is for the capacitor and basically control when the triac is fired based on the characteristics of the diac. By adjusting R2 what we would basically see is similar to the phase shifting of an SCR. The light bulb would dim and go bright depending on when the triac was fired thus determining how