Triac Troubleshoot

[ibwev]

I found a youtube video with a possible starting point for the capacitor and choke size.
**broken link removed**

My apologies. Apparently I am not suppose to attach a youtube address. Here is the picture without the youtube address.

 

[ibwev]

A more common way to do this is to put a resistor in series with the input to the regulator. Divide the voltage you want to drop by the current drawn by the regutor to find the resistor value. The resistor power rating will be v * v / r.

1) Would this diagram be correct?



(Resistor size) = (Voltage I want to drop)/(current from regulator)
=17.4V/.174A
=100Ω

(Resistor Power Rating) = [(Voltage I want to drop)(Voltage I want to drop)]/Resistor
=[(17.4v)(17.4v)]/100Ω
=3.0 W
Derate by at least 2 for a greater than 6w power rating, Digikey has 100Ω/10W resistors

I am attaching my circuit into an existing circuit that uses a 24 VAC transformer. Sometimes, perhaps for extended periods of time, my circuit will only pull 5 mA. This would put the voltage into the voltage regulator at 38.5 V (39 volt supply - 0.5V load (100Ω X 0.005A)). This is 3.5 volts above the maximum amount allowed on the regulator.

2) In what way should I alter the above design if the load from the regulator is less than 4 amps?

 

[Mike odom]

As mentioned before, instead of full wave bridge you could half wave it, that would lessen the size of your resistor somewhat, but if you want to keep the bridge then you could put a 33V TVS device like this one across the input of your regulator: SA28A

https://www.electro-tech-online.com/custompdfs/2013/01/88378.pdf

 

[ronv]

If you change the 7805 to an LM317 you can have a differential of 40 volts from input to output. It is 2 more resistors.
In either case you will need a pretty good heat sink ( 6 or 8 C/watt).

 

[ibwev]

If you change the 7805 to an LM317 ....

Thank you for the suggestion and information. I have a some questions.

1) Should C1 be a 4,700 μF capacitor instead of 470 μF?

2) Since my max current is about 174 mA, I will need to use the LM317M (https://www.electro-tech-online.com/custompdfs/2013/01/lm317m.pdf). Since my output voltage is toward the bottom of the spec, is the Cadj capacitor not needed (pg 7 of datasheet)?

3) Is R3 = 330Ω on the schematic?

4) R2 is listed as 120Ω from your schematic but is listed as 240Ω on the datasheet. Should I go with the datasheet and adjust R3 accordingly?

5) Should C4 be 10μF as listed in the schematic or 1.0μF as listed in the datasheet?

Again, thank you for the help and introducing me to the LM317.