Due to some problems in my project, I am curious about the inner resistance of TRIAC when it turns on. I have run some tests. The setup is just like the schematic picture.
Rs is the source resistance with about 160 ohm. Rg is about 50 ohm. The trigger voltage Vtr is about 2.5V. Then with different input voltage Vs, the inner resistance Rt (resistance between MT1 and MT2) of triac when turning on seems to be varied.
Vs = 20Vpp 1kHz Sine wave, then Rt = 13.8 ohm
Vs = 5Vpp 1kHz Sine wave, then Rt = 26.5 ohm
Vs = 0.5Vpp 1kHz Sine wave, then Rt = 56.2 ohm
Vs = 4V DC, then Rt = 31.1 ohm
My question is that are these values of Rt quite normal? I mean is it the normal case that the inner resistance of TRIAC is about tens ohm and it would decrease with the increasing of Vs. Thank you very much.
(The TRIAC I used is Z0107MN)
simulate this circuit – Schematic created using CircuitLab
Best Answer
When in any doubt, read the datasheet! Fig. 12 gives the (typical, not guaranteed) I/V characteristics.
From this you can see that the triac in the on-state for currents >= 200 mA behaves like a constant-voltage drop of 0.7 - 1.1 V (temperature dependent), plus a series resistor of ¬ 0.33 Ohm. This is the behaviour that you should expect.
(some of) You experiment uses very low currents, which is not what this component is designed for. The latching current can be as high as 20mA, hence the component should not be used below that current.