## Description

SPICE simulation parametric analysis of a light bulb dimmer implemented with a triac-diac and a resistor which can assume a list of values from 1K to 325k. The source is 120V 60Hz.

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SPICE simulation parametric analysis of a light bulb dimmer implemented with a triac-diac and a resistor which can assume a list of values from 1K to 325k. The source is 120V 60Hz.

Felicia–Can I have the analysis of the circuit because I wish to know how is the value being calculated and where is the formula came from? Appreciate and thank you.

ELEKPAUL–Hello Felicia. It’s a basic implementation of a light dimmer. The capacitor C1 is charged across the R1 variable resistor. Lower is the value of the resistor R1 and faster the capacitor C1 charges. When the C1 reaches the breakover voltage of DIAC (30V), Q1 starts conducting, the voltage is applied to the TRIAC gate and it triggers U1.

Felicia–Hello ELEKPAUL, thank you for the explanation. Appreciate it much. So for the capacitor value, we can assume it our own? I wish to build a light dimmer with 230VAC, 50Hz frequency and 2kW power. Can this circuit support the wattage and voltage as well?

Felicia–Hello. I have some question still. I change the input just now to 230V. The Rload i put it as 30ohm as i use the formula P=V^2/R. We know P=2k and V=230V, so R i got is 26 ohm. I choose the 30ohm resistor. After simulating, i found that the waveform for Rdim=300K doesn’t change even though i changed the input and the Rload. Why is it so? How can i alter the input to match my design requirements? Could you please guide me on the formula V=V(A,B)*I(Rload) and the circuit on the right side on the diagram? Why it is needed? Thank you for your help. Appreciate it much.

Felicia–Does the breakover voltage is fixed? What will be affected if i change to lower BV?

ELEKPAUL–Hello, yes you can assume this value for the capacitor. You can change the diac VK value, but 30V is a typical value. The example uses a 120V rms, then 166V peak voltage. if you want to use 230 V (rms I suppose) you have to set the value supply to 325V. With Rload =26 Ohm, the power V=V(A,B)*I(Rload) reaches correctly 2K (watt). A similar triac must withstand current of tens amperes, for I=8.8A it dissipates 7-8 watt, you can calculate this power with the threshold voltage Vto and the dynamic resistance rd from datasheet: P = Vto *I + rd*I*I.

Felicia–Hello. For the formula of V=V(A,B)*I(Rload), is it suppose to be P=V(A,B)*I(Rload)? But shouldn’t it be P=VI? Please guide me on the formula again? You told me ‘you can calculate this power with the threshold voltage Vto and the dynamic resistance rd from datasheet: P = Vto *I + rd*I*I.’ May I know what datasheet I can refer too? I am not clear on the both formula given. Hopefully u can clear my doubt. Thank you very much. =)

Felicia–Sorry, I understood the equation of P=V(A,B)*I(Rload). In my case, my V(a,b) is 325V(Vpp) and my current is almost 8.8A. So 325×8.8 is not equal to 2kW(the power that I want). Please guide me on this problem. And also You told me ‘you can calculate this power with the threshold voltage Vto and the dynamic resistance rd from datasheet: P = Vto *I + rd*I*I.’ May I know what datasheet I can refer too? I am not clear on the both formula given. Hopefully u can clear my doubt. Thank you very much. =) Appreciate your explanation.

ELEKPAUL–yes, I meant P = V(A,B)*I(Rload). Real triacs shows Vto and rd in the datasheet as well as the current that can withstand. Try to download the BTA40 datasheet for example. Pd = Vto *I + rd*I*I refers to the power dissipated by the triac, nothing to do with P = V(A,B)*I(Rload). The power, voltage and current are rms, root mean square, so 2000W/230V = 8.7A rms.

Felicia–From the graph, if my current is 8.7Arms, the power dissipation is around 8W. So does it mean this model of TRIAC is compatible with my project requirement ? (230rms, 2kW max,50Hz)

ELEKPAUL–yes, it can withstand up to 40 amps, of course it needs an appropriate heatsink.

5out of 5luis0802–Hello, which one is the program to open this file extension? , thanks.