Hi I Get lots of email tech na'kal questions in this particular case I Got one from somebody who wanted to know how to design like really low standby power direct mains power supplies ie. you know, 240 volt, a 110 volt mains rectified and powering a product directly non isolated as we'll go into, but they wanted to have like really low standby power. So I like usually a technical questions like these take a long time to answer. so usually I direct people over to the Eevblog our forum to answer such things.

But I Thought: hey, this might make an interesting video. So I thought I'd actually get a mains-powered product like this. In this particular case, it's one of these photoelectric smoke alarms. It's a 240 volt one that actually powers into the mains.

It's actually Joule battery and mains power because if the mains fails, you need the battery back up for safety of course. Model QR 1300 It's a quill which is a big brand here in. Australia So I thought we'd do a teardown of this and have a look at the design and look at how much standby current something like this uses and and potentially how to actually design or a you know one of the ways to actually design a really low standby quiescent current direct mains power supply. So let's take a look at it now.

just a quick card note on the product designer: this thing I Really quite like this. It's got the backing plate here and of course you screw this into the ceiling and then it's got a hinged system like this and It's got some arm screwing terminals for the mains. Of course you've got to have that. so your 240 volts goes directly and they look like proper cage clamps to.

none of that, you know. Springleaf lever? Rubbish. I Really like those? Um, so that's really nice. They've got an extra rack cover which then goes over that to isolate, but when it goes down, here are the pins on the PCB inside.

So when it goes in like this, it goes down and then slides across like that and makes our contact in there as well, retaining it on the roof. So yeah, hats off to the designers there. That's very nice. and we got our 9-volt battery back up in there as well.

And no, it's not a rechargeable issues as a regular, around 9 volt. PPE A3 alkaline or Lithium or whatever you're working there and that just you know, it's probably got Diode. Orion will light, reverse engineer the circuit in here and have a squeeze. But anyway, rather like the designer, that and also the design of this.

this little latch here. When you put the battery in there, it pushes down and moves that lever out and that means that you can't actually close this up and then slide this in any store it without the battery physically being installed. That's a really nice design touch. I Love it! Yeah, this is a photoelectric one as I said photoelectric sensor.

So what that means is that it just like the smoke particles go into the sensor here and then it uses our optical measuring to see if there's any particles within the air inside the sensor so it doesn't have any of that nuclear rubbish. And right off the bat here. the speck. It's only got a maximum spec, but look at this.

80 milliamps, 240 volts Ac. Jeez, that's a fair bit of current draw. But yeah, it won't be that max watch to measure it and there you go. Wow, that is truly horrendous.

563 Millie What's wow? That's awful. And look at the power factor 0.06 to power factor so that gives it a VA of over 909. VA Gotta be kidding me. This is like obviously they're using an like just a bridge rectifier in their Zener diode type configuration or something like that.

Absolutely no thought given whatsoever to actually minimizing the quiescent current of this thing. And what's the big deal? Dave You know it's only half of what. What's the big deal? Well I've done videos which I'll link in on why that can be a big deal and sure your in like residential situations. Generally it might vary in some countries but you're only going to pay for the half of what here.

You're not gonna pay for the 9va here, but that is current that has to come from the grid. So even though you're not paying for it, the grid infrastructure has to be there to enable this. So we're looking at thirty six and a half million at two hundred and forty seven volts. Yes, I Am right on the high side of the mains voltage, which is normally 230 volts here in Australia So to give us our 9va, So that's just yeah, that's nuts.

Let's run some numbers, shall we? So that power consumption is absolutely atrocious, we'll go through the numbers in a minute. But I thought that, well, it may be. it's just this quelled design. So I went out and bought this.

sort of like no-name fire Pro I Guess well, let's check this out. It's not promising though. Look 100 milliamps max. The other one was only like 80 milliamps or something.

So I measure this one. but I reckon it's gonna be a shocker to built down our price and the design of this one is nowhere near as polished as that quell one. Anyway, it's Peridot. Wow.

this is an absolute shocker. 1.3 6 watts. Are you kidding me? That's enormous. Then once again, same power factor as we're getting before.

So our VA is getting nineteen and a half. VA Are you kidding me? People have like half a dozen of these things installed in their house. This is shocking. I'm gonna call it.

This seems to be a systemic design problem with this. with these like the 240 volt home smoke alarms. Let's run the numbers on this. Insane.

So let's run some numbers here. Let's say we had this fire Pro brand installed all over Australia All don't touch the dangerous part here. Yeah, Anyway, let's say we had these. Let's say you know a typical large home might have like five of these installed.

You've got to have them installed in front of every or inside every bedroom and stuff like that. There's new requirements these days. Things let's say we have a million homes in Australia I Think there's like two and a half million. But just you know, let's just round.

let's say we've got a million homes installed with five of these each. right? we're talking. let's just round this up to 20. VA Okay, and because even though the residential customer is only paying for the Watts Okay, 1.3 Watts The grid has to be designed to deliver this entire 78 milliamps, right? You don't get that for free.

That's losses in the grid even though you're not paying for it. So the generator has to produce that. The transmission capability has to be in there for that. So let's just call that our 20 VA right? So this is apparent power or complex power as opposed to real power or active our power as it's called.

But as I said, you've got to have it. You've got to generate this at the generation station. Just goes to show how bad product design like this or really essentially cheap a product design because we'll have a look at better product design in a minute that's more expensive that can solve this problem. This can have a real huge environmental and cost impact on the planet.

When you start talking millions and tens of millions and hundreds of millions of homes that all have these smoke alarms mandated, you don't think other smoke lamps taken a for power and it does when your param from your little 9-volt battery here. cuz normally these things will last a couple of years off a 9-volt battery. so the actual electronics in here detecting the smoke takes NAFA or power it really does. So all of that like 99.9 percent of it is being wasted in the mains rectifier in here and the power supply that needs to power that circuitry.

It's insane and well to the surprise of absolutely none of my audience whatsoever. Armor Yeah, this is the cheap fire pro one and this is the more expensive one. It's actually designed by our kitty I've heard of them before so a yak will don't design their own. but yep, these things are built down to a price as you'd expect.

and we're payin' the price in terms of environmental cost because these mains power sensors use like in the order of sixty five thousand times more power than the equivalent just being powered from the battery. The same thing. It's just insane. Absolutely insane.

And we've got our piezo a transducer as well and this is actually the sensor. You can see where the smokes actually going to get into this one if we have a look at this. Kitty /ak Well one over here you can see that this is where the smoke goes in around here. I Was actually wrong that the smoke goes in through here.

This is actually the buzzer. It goes around the outside and then goes inside the unit and then makes its way through the grill Here into our photo sensor here and here. It's interesting to note that this cheaper one actually uses a tactile switch here for the test button. but the more expensive one over here I Presume it's more expensive actually.

just uses a PCB contact and just some bent metal like that making contact to a link over there. So I Do wonder which ones actually cheaper because yeah, you can get these for cents at the Shenzhen market. I Wonder how much this solution here cost? It's interesting. Anyway, this one.

Is this a double size? This one looks like a double sided Fr4 board. This one over here. single sided job. You should save a few cents on that.

Anyway, both of them have a mod because you don't want any surges. of course on the power line because these things are hooked up are 24/7 so both from have a little more that one's got a little last slot cut out underneath for isolation. but basically it's a capacitive divider and a big resistor capacitor. Of course at 50 Hertz none of that 60 Hertz American rubbish 50 Hertz Australian Mains.

And of course a capacitance will have a given impedance and then that works in combination with a resistor here to give you a resistor divider and it looks like is that ours interrupt? There could be so this one users of one mic both of these x2 our class capacitors. Of course you know a proper mains rated self-healing tights with all the requisite approvals on them. So this is the kitty slash quill. This is the fire pro here.

you've got a smoke alarm our controller I See here, it's a custom. ASIC We've got bridge rectifier I'm down here I Can't see a bridge rectifier over on here. It might be a just a half-wave job II Not sure if you can see that, but the more expensive one there you go. got the shine on it.

It looks like it has a at least partial our conformal coating on it just to stop our moisture causing a problem. So I've reverse engineered the mains input power supply on both of these and as suspected, there are just a simple Zener diode based rectifier. That's it. So we've got our 240 volts in here, line and neutral.

We've got a series resistor here that's a bigger to what job' in both places. Then we've got that X to 240 volt rated. you know, mains capacitor. We've got a mob here.

doing some protection after the resistor, so that's good. We've got some bleeder resistors across here. just some high value. Once, one of them had three resistors in series just to get the voltage because they're SMD one.

so they're only rated like couple hundred volts each tops. so they put them in series to get the voltage rating. Then we've got a A Zener diode. In the case of this one, it actually used.

Sorry. This one over here used to Zener diodes here and here in series. This one over here only uses one Zener diode but works exactly the same. Then we just got a regular Joe Bloggs diode here and then an electrolytic cap and then that buggers off to the ground in here.

Now of course. these are what's called a direct mains connection, non isolated power supply, and these are inherently dangerous. Do you do not design these? except in products that are fully enclosed like this, where the user can never, ever touch the electronics in them? Or shouldn't That's the entire point because it's more cost and complexity to put in like a mains, isolation, transformer, and everything else. But in these types of products, um, it's It's no problem.

and it's completely legal to have your circuitry over here mains referenced over here even though it's the neutral. And technically we use the Men system, the multiple earth neutral is we do here in Australia Your mileage may vary and the neutral is connected back to the earth at your switch box, but you can't assume that the wiring in a house is correct and some idiot may have swapped. You know, active in neutral here and you could completely come a guts or if you had designed a product that was relying on the fact that any exposed user accessible ground or metal or connector or anything like that was reliant upon directly connected through the neutral, you're going to come a gutter and that's inherently unsafe, so you don't want that. So a non isolated power supply like this.

um, they're very common to find in these type of in sealed enclosures like this because you just don't need the isolation. But this is where the poor power factor comes from. It's just using the cap and the series resistor as a dropper effectively for the Zener diode. and that's just no, No, that's what's resulting in the piss-poor power factor the one that we're seeing.

So there's just no way of avoiding losses in your traditional Zener based a circuit like this. I In this particular case, I'm going to measure the voltage directly across the hundred ohm resistor here. got it there. And seven Point Nine volts.

So there you go. That's seventy Nine Milliamps. And of course, that's going to match the seventy-nine milliamps up here. And there's absolutely nothing you can do about that.

So you piss in a way. That's seventy Nine milliamps. Even though you've got essentially bugger all like micro amps load on here, It doesn't matter, it's just been wasted in the Zener Diode circuit. So that's just lazy and cheap design.

and well, they just didn't care. And of course, Eighty-nine Millionaires might not sound like a lot, but when you have millions and millions, tens and millions, hundreds of millions of these sort of things out there, it makes a huge difference, especially given the poor power factor that current has got to come from the generation system. There's just and he got I squared our losses in the in all of that and it's just it. It adds up and if you want to know how much current it takes with just the 9-volt battery are parents.

So your traditional iced mocha lime in and this particular one five Littles five My cramps. It sort of just goes up in births it's You know, its sense in there. Whatever. Max, you're almost fifty my cram.

So between 5 and 50 microns, they're periodically so you know, sniff of an oily rag stuff. So if the actual product itself only takes like less than 50 my cramps, why does the whole product have to take orders of magnitude more than that? Because they were just saving cost here and they just didn't care about how much quiescent power consumption this thing is going to use. and that's terrible just to save like maybe a dollar or something like that on each one. And yeah, I can understand that might be significant, but if you explain to people, hey, look, our one is gonna save you money because there's not a quiescent current in there.

But you could turn this into a marketing opportunity. you can say hey, look, our one only draws like a hundred microns for example, or a couple hundred my cramps like so but one milliamp for example. if you just spent you know a dollar or two more in the design of this thing and you put some thought in you, could you know you can own the market because yours has it like lower power consumption I Anyway, I don't Is there one out there that claims that? I don't know. So how can we improve this? Well, let's go have a look at well, at least one solution anyway, but it's going to be more expensive and that's the trick.

So how can we solve this? Well, there's many ways to skin this cat and if you've got a better way to skin this cat, then please list it down below and you can roll your own solutions and do all sorts of stuff. But I'm just going to go with incredibly simple and obvious solution. Let's take a look, let's go straight to Digi-key shall we or your favorite supplier with their parametric our search tools all as I've shown in previous videos. You can go directly to the manufacturers' websites like over here for example and look at audio regulators and stuff like that.

Now we're just gonna. we need a regulator. Of course there are these particular power sensor runs on 15 volts. so actually the chip runs from 6 to 15 volts.

but this particular one has light runs on 14 and a half volts a Zener diode voltage in this thing. anyway. So we need a linear regulator, but because it is powered directly from the mains, we don't have any isolation. We need a high DC input voltage regulator and these actually do exist.

So if you just simply go into the voltage regulator linear voltage regulator section here in De Jakke and then you sort by voltage input maximum right here Such from the highest down look you'll notice that is a whole bunch of them that have 450 volt rated and then it drops down to 150 150 is that's not good enough. But obviously these 450 volt ones are designed for direct mains connection. And look, there's a microchip solution. There's a non semi solution.

Yep, they seem to be the only two, but hey, there's two right off the bat. So we can go into the microchip or one here. Adjustable 1.2 two, three, or four hundred thirty-eight volt output regulation. This one's not the best example.

Let's go to a better one. Now let's go to what these on semiconductor ones here. You can find it on the parametric search on directly on the website here. Wide input voltage range ultra-low quiescent current.

that's what IQ means. Quiescent is current. Queue is quiescent up to ten milliamps load current so only designed for real low-power stuff. but hey, you just saw the circuit consumption is only like 50 micro amps.

So this has got oodles. Um I don't like that little pain-in-the-ass package? Look at that surface mount so this one's not really conducive. but look you can. Its design for half wave rectifier mains input circuits with the 4.7 mic cap there.

that's you will see in a minute how that's not we can get one that's a bit better than that. But if we go down here, look here's some input going configuration. There's a half wave. a bridge rectifier.

look Bingo! 15 volts out 10 milliamps. It's going to do the business. We've got a full wave our bridge rectifier one here. Let's have a look at this other one.

So they've got to once. The NCP 1786 we saw before. this is the 1785 Product Overview: It's one of their energy-efficient innovations. here.

They look: Oh Shock Horror designed for smoke sensors. The marketing people that these companies know exactly how to target these chips to these companies. but do they care? There's probably some out there that implement these lower power solutions, but well, the two I've got here don't They just saved a few cents or see the cost in a minute. But anyway, let's have a look at this puppy, shall we? It's got a fixed 15 volt output exactly what we want, and half wave rectifier 2 point 2 micro farad cap.

The smaller the capacitor, the cheaper it's going to be to actually implement that. So there you go there. there's your there's your circuit right there. Just a half-wave diode bridge rectifier 2.2 mic cap 450 volts has got to be proper mains, raid and all that sort of stuff.

You still. Yes, you're still going to get poor power factor from any bridge rectifier solution like this, but we'll take a look at a smarter solution to this in a minute. It's really quite nice, but still because you aren't implementing that Zener solution, that's just peace, You know, hi Like a demon. Hi! They could have just implemented the Zener diode circuit better, But anyway, these are going to be a better solution because the quiescent current is only like a 10 micro amps quiescent current there, and 50 micro amps for the load.

So it's draw enough. All right. the whole thing, even probably the worst smoke sensor circuit on the chip on the market is, you know it gonna be like some hundred micro amps with this thing. So yeah, we're still gonna get poor power factor, but it's gonna be like the order of magnitude better than the Zener solution that they're actually using here.

no doubt about it. So it literally is. as is. as simple as that.

and tell us the price, son, how much does it cost Here we go. Yeah, they cost okay. Fifty-five Yankee cents each in like volume. probably get in cheap.

and now if you're manufacturing millions of smoke alarms, right? So they probably saved like 30 cents or something. 40 cents or something because the Zener diodes a cheap. You get them from the Shenzhen market and it like it. It's real cheap right the way they did it.

So they probably saved like a sub $0.50 on the bond cost of this thing. and they're just, you know, destroying the environment and putting load on the grid. And they because they just don't care, they want to say 30 cents. It's ridiculous.

Should it just use one of these puppies? Well I know you're asking. Is there a smarter solution than just the simple diode, full or half wave bridge rectifier diode solution here to get a better power factor? Well yes there is. As I said, you could probably roll your own and let us know if you've got links down below to like rolling your own solutions. We won't go into that.

It's a it's fairly complex, but I Did find this part from Ti. It wasn't easy to find, but look at this. it's a hundred and twenty milliamp smart. AC DC Low dropout linear voltage regulator.

Don't know why you need low dropout, but anyway, you've got plenty of margin, but it's for non isolated power solutions greater than 18 volts same as before standby power consumptions only 15 milli watts. Their line voltage capped cap drop capacitor as small as 1/4 the size of linear solution. So there you go. You can save cost there because when you've got mains rate of capacitors, they have to be not only physically larger, but they're more expensive as well.

I Have a look at this part because it's really quite interesting. Yes, it's about I think it's about $1 in volume here. But anyway, work with me. Well, what do you know? Smoke and heat detectors.

They know who they're marketing to. Now here it is a schematic for half wave and full wave bridge rectification. This is direct mains input. So here's your 240 volt mains input.

You've got a T Vs surge protection here. You've got an input series capacitor and input series resistor just like we have on the Zener circuit here. but instead of having the lossy Zener circuit we're putting in this active rectification chip. Just got a few other us supporting a components there, but it gives you an audio regulated voltage out from direct mains input and the way it does it is really quite nice.

Let's go down here is that it's got a rectification in here so instead of having dumbass regulation, it's got this active reading regulation. with these are two MOSFETs here and here which are control this full wave bridge rectification and it's very smart. It can control it so it can give you a better power factor direct from the mains. Anyway, it's just a really nice chip.

I like this one. So if you're after a direct mains connected, low quiescent current solution and with direct linear voltage regulator output not isolated of course then I This is well worth a look. And yeah, it's a bit expensive it. you know, a bucket chip, but um, it's a really nice solution.

You want the lowest quiescent current possible, this could do the business. Unfortunately, this chip is only available in versions that we've fixed output voltages up to 5 volts. It doesn't go to 15, don't know why you know. but anyway, so it's not suitable in this particular circumstance with this particular smoke sensor chip.

Anyway, I Thought I'd show you that because that is a really nice solution chip if you know of another equivalent one on the market direct AC input like this. Um, please leave it in the comments down below because I think this might be the only one. but anyway, haven't done a hugely exhaustive search. but yeah, I really like that.

That chip of the week I Think it is. So there you go I hope you enjoyed this. Look at a typical Who consumer product that went from being very low-power design through essentially regulation. At least here in Australia you have to have these are direct or I think all new houses must have these direct mains connected smoke sensors and two of them on the market, including one of like a real premium Batt brand one of the most popular ones.

They're both still awfully designed, penny-pinching design and not giving one rat's ass about the quiescent power consumption. And as I showed when you've got millions of these things installed, some houses have you know half a dozen or more of these things then it just really adds up. So next time, if you're involved in designing stuff like this, just please try and persuade the company that you're working for that This could be a potentially good and marketable solution because you can take a hey Houses eco-friendly everyone goes crazy over that these days. marketing people can tell the consumer about this sort of problem and this is by far not the only product there's you know and countless other products on the market.

If if you know of any other really badly designed products that have standby Quiescent Power Light, there's basically anything with Internet of Things in the title. Possibly anyway, leave it in the comments down below. So yeah, it's a real eye-opener when you actually run the numbers and do the calculation on something like this of how much actual Grid infrastructure and generation power is wasted just through poor product design like this. Unbelievable.

So anyway, I hope you found that video useful. If you did, please give it a big thumbs up. And as always you can discuss down below or over on the Eevee blog forum and check out evey blogger TV which licks to my library' channel subscribe over there because that's going a gang busters and I did mention chip of the week Yes! I'm back into doing more regular amp hour episodes. so if you don't know World's biggest Electronics Engineering Podcast said I've only been co-hosting for the last decade almost.

um, the NPR comm. Go check it out available on all your I Chinese platforms and Spotify and all that sort of stuff. Catch you next time.