Need help getting a control signal to a TRIAC

Thread Starter

Anex

Joined Dec 4, 2017
16
I'm trying to make a schematic, where one IR motion control light switch turns on only one light and another IR motion control switch turn on both lights. I have tried many things, especially diodes which I have currently set up, and work almost perfectly, but the problem is that one light is aggressively flickering, since it only gets one sine wave, the other gets cut by the diode.

Here is my current set-up:
chrome_GcTOAg5f3t.png

This is a crude approximation for the spotlight and LED driver + strip schematic, but for all intents and purposes, it is roughly right.

I need help getting a control signal for the TRIAC. I want the TRIAC to turn on the LED light when IR switch #2 is switched. Im not sure how to get a control signal yet, I tried using bidirectional optocouplers or maybe it just needs a resistor from somewhere, but always the other sine wave half makes the schematic a bit too complicated. Also tried some sort of latching schematics, but it also gets way too complicated.

I want to lessen the number of parts to avoid the risk of electrical hazards or fires.

I'm familiar with power electronics and mains, but a newbie to control signals, TRIACs and etc, but I'm hoping with your help to learn a bit more. Maybe this doesn't even need a TRIAC.

TLDR: Need help getting the TRIAC to turn on with IR switch #2 and off otherwise.
 

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Dodgydave

Joined Jun 22, 2012
11,302
Easiest option is to modify the ir sensor output to make two outputs, then they can be put in parallel, what are the sensors you are using?
 

Thread Starter

Anex

Joined Dec 4, 2017
16
Easiest option is to modify the ir sensor output to make two outputs, then they can be put in parallel, what are the sensors you are using?
The IR motion sensor has three pins, one for line in (L), other for switched output (L1) and other for neutral (N). I'm fairly certain, that it senses motion, which in turn switches an internal switch to give voltage at the output L1. So it is a one output switch. Can I make two outputs externally?
 

Dodgydave

Joined Jun 22, 2012
11,302
The IR motion sensor has three pins, one for line in (L), other for switched output (L1) and other for neutral (N). I'm fairly certain, that it senses motion, which in turn switches an internal switch to give voltage at the output L1. So it is a one output switch. Can I make two outputs externally?
It's probably a Triac output or it could be a relay, need to see inside it ..
 

Thread Starter

Anex

Joined Dec 4, 2017
16
It's probably a Triac output or it could be a relay, need to see inside it ..
There is definitely a click once it activates. It must be a relay. I'll take a look inside a bit later, maybe there is a NO and an NC pin inside.

In the meantime, how would one go about using the two pins of a motion sensor to create a one-light and two-light activating circuit?
 

DickCappels

Joined Aug 21, 2008
10,169
Or, if you don't want to modify the sensor, use the output of that relay to control a double pole relay. Be aware of the contact ratings (mainly voltage) on your sensor.
 

Thread Starter

Anex

Joined Dec 4, 2017
16
Or, if you don't want to modify the sensor, use the output of that relay to control a double pole relay. Be aware of the contact ratings (mainly voltage) on your sensor.
That is actually very clever. I think I will use a 10k resistor from the first relay inside the motion sensor to give current to the DPST relay. Thank you very much.
 

Thread Starter

Anex

Joined Dec 4, 2017
16
That is actually very clever. I think I will use a 10k resistor from the first relay inside the motion sensor to give current to the DPST relay. Thank you very much.
Actually never mind, the output will be AC and i need DC, otherwise it will be continuously switching. I think ill try to resolder it inside the sensor.
 

RPLaJeunesse

Joined Jul 29, 2018
254
Reverse the direction of pins A1 and A2 for the triac in your diagram. Add 2 resistors in series across the LED spotlight, connect the center point to the triac gate pin.. Size the resistors to 1) limit the gate current with IR switch 2 closed, 2) keep triac off when IR switch 2 is open, and 3) limit resistor power dissipation to a safe value.
 

Thread Starter

Anex

Joined Dec 4, 2017
16
Reverse the direction of pins A1 and A2 for the triac in your diagram. Add 2 resistors in series across the LED spotlight, connect the center point to the triac gate pin.. Size the resistors to 1) limit the gate current with IR switch 2 closed, 2) keep triac off when IR switch 2 is open, and 3) limit resistor power dissipation to a safe value.
Oh wow, it was actually very simple. In case the relay mechanism doesn't work, ill try this setup. Since the spotlight led limits the current to about 150 mA with its internal resistance, I should be able to easily use two resistors of 20 ohms.
 

RPLaJeunesse

Joined Jul 29, 2018
254
Oh wow, it was actually very simple. In case the relay mechanism doesn't work, ill try this setup. Since the spotlight led limits the current to about 150 mA with its internal resistance, I should be able to easily use two resistors of 20 ohms.
Please reread my post, the resistor string parallels the spotlight, spotlight current is immaterial. Calculate your resistor values carefully, 20 Ohms is way off. The A-G resistor is somewhat arbitrary, but likely is in the low kilohms. The resistors will NOT be of equal value, and other should be in the many kilohm range.
 

Thread Starter

Anex

Joined Dec 4, 2017
16
Please reread my post, the resistor string parallels the spotlight, spotlight current is immaterial. Calculate your resistor values carefully, 20 Ohms is way off. The A-G resistor is somewhat arbitrary, but likely is in the low kilohms. The resistors will NOT be of equal value, and other should be in the many kilohm range.
Ah, my bad. I understand my mistake and it changes everything (Sorry, English is not my first language, and when I read across I thought it meant in series with LED). In the parallel case, 20 ohms won't do indeed. I have a few 1k and 10k ohm resistors, I will try those. Wonder what the ratio of the two resistors should be? Would 10:1 be a good start?

Since I don't feel confident enough with this setup long-term, I will only use it to see if it works and then take it apart. It's for the best.
 

RPLaJeunesse

Joined Jul 29, 2018
254
... I have a few 1k and 10k ohm resistors, I will try those. Wonder what the ratio of the two resistors should be? Would 10:1 be a good start? ...
Its not so much a ratio, but approximate values that need to be determined. The smaller resistor is set by minimum gate trigger voltage and maximum gate leakage current in the "off" condition. Figure that resistance number and use a value maybe half of that. The larger resistor is determined by the ratio of maximum line voltage (at peak) to the maximum allowed gate current. The resistor power rating should be more than the product of those two values. Not knowing your triac or line voltage I can't suggest actual numbers for these two resistors.
 

Thread Starter

Anex

Joined Dec 4, 2017
16
Its not so much a ratio, but approximate values that need to be determined. The smaller resistor is set by minimum gate trigger voltage and maximum gate leakage current in the "off" condition. Figure that resistance number and use a value maybe half of that. The larger resistor is determined by the ratio of maximum line voltage (at peak) to the maximum allowed gate current. The resistor power rating should be more than the product of those two values. Not knowing your triac or line voltage I can't suggest actual numbers for these two resistors.
Oh, I see now. I was a bit confused about where to start with figuring it out. Looking at the triac's datasheet (It's the T405-600H)
and the minimum gate voltage is Vgt = 1.3V, the minimum gate current is Igt = 5mA and maximum gate current is Igm = 4A. (Mains is 230V, so peak would be 325.3V)

Im thinking of using a 30k 1W power resistor. I'm not sure how to determine the gate leakage current, however, therefore cant figure out the smaller one.
 

RPLaJeunesse

Joined Jul 29, 2018
254
With Igm at 4A I'm thinking just use the LED spotlight in place of the high value resistor, saves wasted power. Connect LED spotlight to the gate, the lower value resistor gate to (A1 and input power). The datasheet absolute maximum Idrm is 1mA, if this leakage was to the gate a 470R from gate to A1 terminal would keep the gate well below turn-on. A higher value might work fine as well if the LED strip doesn't get enough voltage.
 

Thread Starter

Anex

Joined Dec 4, 2017
16
With Igm at 4A I'm thinking just use the LED spotlight in place of the high value resistor, saves wasted power. Connect LED spotlight to the gate, the lower value resistor gate to (A1 and input power). The datasheet absolute maximum Idrm is 1mA, if this leakage was to the gate a 470R from gate to A1 terminal would keep the gate well below turn-on. A higher value might work fine as well if the LED strip doesn't get enough voltage.
Oh, so is the Irrm the leakage current? That is useful to know.

So if I got it right, the circuit should be something like this:
chrome_FugZMlwUS8.png

Just double checking to make sure.

In simulation seems to be working in order.
 

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