Switch a power supply on and off with a TV?

[MikeMl]

Beware any SSR that comes from EBay; they are usually fakes...
Most of the DigiKey SSRs do not require R1, D1, TR1 or extra DC power supply shown in Ron's circuit. If they say 3V to 12V input or higher, no current-limiting resistor is required. Just drive them directly from the switched 5V (observe polarity).

 

[AznGothic]

OK, here is what is going on. First, a LED is a current device so hold that thought. Now inside the SSR is a LED and in this case according to the data sheet that LED has a forward working voltage of 1.2 volts which is pretty typical and a forward working current of 20 mA or .020 Amp. If we were to directly apply 5 volts across the LED it would draw much greater current and burn up. So we need to limit the LED current. In this case limit that current to 20 mA. We know the LED forward voltage drop is 1.2 volts so if we apply 5 volts we can say 5.0 - 1.2 = 3.8 Volts. Therefore I can say 3.8 Volts / .020 Amp = 190 Ohms. This all goes back to Ohms Law.

So now if we look at the circuit I posted above if resistor R1 is dropping 3.8 Volts and the SSR internal LED is dropping 1.2 Volts there is our 5.0 volts and the circuit current will be 20 mA. The small problem is that 190 Ohms is not a common off the shelf resistor. Common off the shelf values would be 180 Ohms or 200 Ohms. We could get by using either value. Generally the next higher value is selected so we would use 200 Ohms. Doing so will slightly lower the current but not enough to likely matter.

Yes, the current draw off the 5 volt pin or 5 volt supply will be limited to 20 mA.

Ron

I totally missed the link that said "Datasheet" on that page. That's where I got confused where you came up with .020 from. Thank you for the explanation. I clicked the datasheet link and see where it says Vf 20ma, 1.2V and 1.4V Max. By my calculations, a 200 Ohm would drop it to 19mA and a 180 Ohm would raise it to 21.1mA? Lowering it to 19mA would also essentially make the SSR last longer as well? Will a 1/4W resistor do just fine?

A lot of modern TVs have a relay to connect power to the main power supply. That is what make the click when they turn on. The receiver for the remote is left on all the time, run from a separate, much smaller, power supply. This keeps the power low.

If that is the case in your TV, you could just run the power supply for the LEDs from that same relay.

I just took a picture of the TV's power supply. I see a bridge rectifier on the top left. A coil is under that. Then a metallized polypropylene film capacitor under that with another coil. And then there's the fuse and AC input. I don't see a relay anywhere?

 

[alec_t]

I don't see a relay anywhere?

What is the black rectangular thing in the top right corner, just below the four connectors?

 

[AznGothic]

Beware any SSR that comes from EBay; they are usually fakes...
Most of the DigiKey SSRs do not require R1, D1, TR1 or extra DC power supply shown in Ron's circuit. If they say 3V to 12V input or higher, no current-limiting resistor is required. Just drive them directly from the switched 5V (observe polarity).

I pretty much order everything I use from DigiKey. Love that site. I just don't understand it half the time. The SSR I linked is from DigiKey and says its a 1.2VDC input. Reloadron said it would work just fine, I would just need to add the 200 Ohm resistor to drop the 5VDC output from the board to a 1.2VDC. The datasheet says the max this SSR can take is 1.4VDC. I won't be using TR1 but I will need R1 and I think just to be on the safe side I'll add in D1. I don't think I need the snubber so I'll just omit that as Reloadron said.

What is the black rectangular thing in the top right corner, just below the four connectors?

I believe you are referring to the PCB the 4 connectors are soldered to. Here's a close up pic of the 4 connectors.

 

[AznGothic]

Beware any SSR that comes from EBay; they are usually fakes...
Most of the DigiKey SSRs do not require R1, D1, TR1 or extra DC power supply shown in Ron's circuit. If they say 3V to 12V input or higher, no current-limiting resistor is required. Just drive them directly from the switched 5V (observe polarity).

I pretty much order everything I use from DigiKey. Love that site. I just don't understand it half the time. The SSR I linked is from DigiKey and says its a 1.2VDC input. Reloadron said it would work just fine, I would just need to add the 200 Ohm resistor to drop the 5VDC output from the board to a 1.2VDC. The datasheet says the max this SSR can take is 1.4VDC. I won't be using TR1 but I will need R1 and I think just to be on the safe side I'll add in D1. I don't think I need the snubber so I'll just omit that as Reloadron said.

What is the black rectangular thing in the top right corner, just below the four connectors?

I believe you are referring to the PCB the 4 connectors are soldered to. Here's a close up pic of the 4 connectors.

 

[Diver300]

I don't see a relay anywhere?

Unfortunately, I don't think that there is one on your TV. There is a yellow transformer with black ends, and I was expecting to see a small one of them to run the receiver for the remote control. It seems that my idea isn't going to work on your TV.

You could just plug the TV into one of these:- **broken link removed**

 

[AznGothic]

Unfortunately, I don't think that there is one on your TV. There is a yellow transformer with black ends, and I was expecting to see a small one of them to run the receiver for the remote control. It seems that my idea isn't going to work on your TV.

You could just plug the TV into one of these:- **broken link removed**

The IR receiver for the remote control is on a PCB with the On/STBY light which has a ribbon cable running to the logic board. So I'm assuming it is micro controlled instead of using a relay. Someone else showed me those Master/Slave power strips that turn things on and off by sensing when you turn your TV on or off. I think they are really awesome power strips and will probably get one for future projects but for now I want a learning experience. I'm having loads of fun with this project and that smart power strip would just take the fun away lol. Thank you though for the recommendation.

 

[Reloadron]

Yeah, to answer your question back there a 1/4 watt 200 or 180 Ohm resistor for R1 would be fine.

Ron

 

[AznGothic]

Yeah, to answer your question back there a 1/4 watt 200 or 180 Ohm resistor for R1 would be fine.

Ron

I used a circuit calculator thing and it said the power would be around 68mW. I ordered a 1/4W, 1/2W and 1W resistor just in case since I didn't know which to use. 68mW would be less then 1/8 of a watt right?

 

[Diver300]

I used a circuit calculator thing and it said the power would be around 68mW. I ordered a 1/4W, 1/2W and 1W resistor just in case since I didn't know which to use. 68mW would be less then 1/8 of a watt right?

Yes. 1 mW is 0.001 W, and 68 mW can be written as 0.068 W.
1/8th W is 0.125 W.

 

[AznGothic]

Ok, sweet. Thank you everyone. I have the resistor, power supply and solid state relay on the way along with some plexiglass to use as a light diffuser. Can't wait to finish this up.

 

[Reloadron]

Ok, sweet. Thank you everyone. I have the resistor, power supply and solid state relay on the way along with some plexiglass to use as a light diffuser. Can't wait to finish this up.

Post back and let us know how it works out.

Ron

 

[AznGothic]

Post back and let us know how it works out.

Ron

I got the power supply in the mail today. The rest of it should be here tomorrow. I'll definitely tell you guys how it all works out. Do you know if I'll need to mount this SSR to a heat sink?

 

[Reloadron]

I got the power supply in the mail today. The rest of it should be here tomorrow. I'll definitely tell you guys how it all works out. Do you know if I'll need to mount this SSR to a heat sink?

Looking at the data sheet it looks like the tab allows for a 6-32 screw so I would find something to use as a heat sink and attach the SCR with a #6 screw and nut. Use a little thermal compound if you have it. I doubt it needs to be fancy and make sure you look at the data sheet for the correct pinout. Remember too, the tab is common to pin #1. That is important! Real important!

Ron

 

[AznGothic]

Looking at the data sheet it looks like the tab allows for a 6-32 screw so I would find something to use as a heat sink and attach the SCR with a #6 screw and nut. Use a little thermal compound if you have it. I doubt it needs to be fancy and make sure you look at the data sheet for the correct pinout. Remember too, the tab is common to pin #1. That is important! Real important!

Ron

Ok, so looking at the data sheet, if the tab is common to pin #1 that means the tab will be energized with 120VAC when the relay turns on. That doesn't sound very safe. So if I put it on a heat sink (data sheet says heat sink is optional, don't know how optional) then the heat sink will also be energized to 120VAC. How does that work? Even if I put the SSR inside the TV and used the TV as a heatsink (entire back side of TV is metal) then the entire TV would be energized. If I mounted it to the heat sinks on the TV power supply, that would energize the heatsink and pass to what ever is mounted to that heatsink and ruin it wouldn't it? I'm confused....

 

[Reloadron]

What it means is the tab being common to pin one (the hot out) is when the device is mounted to a small heat sink that heat sink is hot with 120 VAC. Therefore the tab and heat sink must be isolated. This is not unusual for devices like this where the tab is common to one of the pins. So yes, in a nutshell you can't just mount this to an existing heat sink or real bad things will happen. I would just cut a small piece of aluminum or copper sheet and make a small heat sink and keep it isolated. You can likely buy a small tab type heat sink at a local Radio Shack.

Ron

 

[AznGothic]

Got the rest of the stuff today. I'm looking at the SSR and the entire back is epoxy. There are 2 small metal pieces on the front of the tab where the arrows point to in the data sheet. I was expecting the entire tab to be metal like on a MOSFET. So that means it should be fine to just mount this to any heat sink including the heatsinks on the TV power supply right? Since the entire back piece is epoxy it shouldn't be able to make anything it is mounted to energized with 120VAC. It would only make something hot if it touches those small metal areas that are exposed on the front.

 

[Reloadron]

Using an ohmmeter measure between the metal and the pins. Pin one should be common to the metal and mounting hole. Next, I haven't a clue what is mounted to this existing heat sink or what potential the heat sink may or may not be at during normal operation with respect to ground. My recommendation is to give this SSR its own heat sink, they are easy to fabricate.

So that means it should be fine to just mount this to any heat sink including the heatsinks on the TV power supply right?

Since I can't see what you have I can only advise against using the existing heat sink. Maybe you can and maybe you can't but I will not tell you to go ahead and no problem.

Ron

 

[AznGothic]

I tested it. The small metal exposed pieces are common to pin 1. The mounting hole has no exposed metal, it is completely covered in epoxy except for the pins and the 2 small exposed pieces on each side of the tab. But I have a new problem. I have a wire coming off of the 5VDC (turns out its only 4.89VDC) ON/OFF pin of the TV power supply going to the 200 Ohm resistor which then goes to the positive input side of the SSR. The negative input of the SSR is going straight to chassis ground. Then I have pin 1 of the output going to AC neutral and pin 2 of the output going to the laptop charger neutral side. The hot side of the laptop charger is going straight to hot 120VAC. I powered it all on and I get no lights. Not even the LED of the charger turns on. So I tested the SSR. Tab to pin 1, Tab to neutral, pin 1 to neutral, 120VAC to the tab (I got 124.3VAC), 120VAC to pin 1 and finally 120VAC to pin 2. Going to pin 1 I got power (naturally) and going to pin 2 I got around 200mV. Now when I power the TV on, I tested pin 2 to 120VAC which I should be getting 120VAC but instead I got 3.6VAC. Is this SSR bad?? Or did I do something wrong? (I hope I was clear in my explanation and not confusing.)


EDIT: Oh, and when I tested the DC input side I was getting roughly 1.101VDC.

 

[Reloadron]

The 4.89 VDC shouldn't be a problem. Worst case R1 could be lowered.

Also, all SSRs have leakage. That means with no control voltage applied it isn't unusual to measure a voltage at the SCR output with respect to ground. Once a load is placed out there the voltage will go away till the SCR is turned on with a control voltage.

Let's look at the drawing:

The AC Line Hot should be going to Pin 2 and the AC line Neutral to the Neutral side of the Load. Pin 1 goes to the load Hot. That what you have?

Just saw your edit. Yes, if you measure across the DC input side that sounds about right.

Ron