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Does an AC to DC power brick need pure sine wave or will it be fine on a modified sine wave cheap inverter?

greengooseman

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Do AC to DC power bricks need a pure sine wave 120VAC to operate properly? Or can you use a much cheaper modified sine wave to power it? Power bricks for same gaming laptops can be as high as 300W or more I suppose. I was also considering the AC to DC brick for my solar generator. (AC200).

I know fans and motor type devices need a pure sine wave inverter. Does an AC to DC brick really care?
 
I think a DC-DC converter will be a better solution to power a laptop instead of using an inverter - especially since the „power brick“ is probably a switching type which can be hard on inverters due to its dynamic load characteristics.

I’ve used a number of smaller laptops successfully using small DC-DC converters. Have a look at this link for more opinions and experiences:

could-a-modified-sine-wave-inverter-destroy-damage-the-ac-adapter-for-a-laptop

(The term „modfied sine wave“ is a marketing euphemism. The output waveform is essentially a square wave with one added harmonic. You’d need much more than that to even remotely approach a sinewave. It’s a bit like knocking off the corners of a square - would you call that a „modified square“ or a „modified circle“?)
 
It is possible the front-end of a switching supply (brick for laptop) would not be bothered by "modified sine wave" (which I call "modified square wave") because it is just diodes and capacitor. A PF corrected supply might be offended.

Simply using a DC-DC converter likely would not work because a high-end laptop won't draw full power from an unrecognized supply. Laptops draw more watts than can be delivered through typical connectors at proper voltage, so if they recognize compatible model supply they request boosted voltage.

A supported 12V car adapter for the laptop might work. Although, cigarette lighter outlets wouldn't be expected to deliver all that much current either.

My Dell laptop sometimes doesn't recognize its own supply so that provides fewer watts.


 
Do AC to DC power bricks need a pure sine wave 120VAC to operate properly? Or can you use a much cheaper modified sine wave to power it? Power bricks for same gaming laptops can be as high as 300W or more I suppose. I was also considering the AC to DC brick for my solar generator. (AC200).

I know fans and motor type devices need a pure sine wave inverter. Does an AC to DC brick really care?
I can say that a pretty large selection of them survived two weeks on my modified sine wave generator in Florida. They included laptops, modems, routers, television, TiVo, a 10k BTU air conditioner and a fridge. That said, I will be replacing it with two smaller parallel capable sine wave generators, but mainly for the lower noise factor.
 
I have both for my Lenovo Y50 gaming laptop, it uses up to 90W. It's getting a bit old but still plays my favorites well.
110v AC input power brick works well with cheap inverter. No surprise to this old techie. AC is likely rectified and charges a cap before switching down to lower voltage. I generally do not do this.
12V DC - DC 20V converter is far more efficient. It too is rated 90W. The laptop complains its not good enough, but only one time I found it to be true. BTW: Before I bought the 90W, I had a Lenovo 60w DC-DC converter which was useless with the laptop on, but would charge the batteries when it was off.
Gotcha: 12v cigarette lighter sockets are typically rated and fussed for 10A. Look hard and you might find true 15A. That's a range of 120W to 180W if battery voltage and wire resistance is ideal. As the voltage drops the current increases to keep the DC-DC output voltage steady.
 
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Do AC to DC power bricks need a pure sine wave 120VAC to operate properly? Or can you use a much cheaper modified sine wave to power it? Power bricks for same gaming laptops can be as high as 300W or more I suppose. I was also considering the AC to DC brick for my solar generator. (AC200).

I know fans and motor type devices need a pure sine wave inverter. Does an AC to DC brick really care?
I am curious why you say motors need pure sine. In the 1970s all motor drives were 6-step, or modified sine. I did a comparison (many years ago) between motor temperatures running on both types. I recall that the increase in the motor temperature was almost too small to measure. I really cannot understand why inverters are made with modified sine anyway. The cost to produce either design is almost the same.
 
I have a square wave inverter in my truck. It gets used a lot. My Dell and Samsung laptops have never minded the square wave.
 
Newer Dell desktops have PF correction so want sine-wave only.
Maybe laptops will at some point. Maybe documentation on the laptop or power supply would indicate that, but they probably don't consider running it off a UPS; the laptop is its own UPS. So look for mention of power-factor correction.



"much cheaper modified sine wave"

300W power supply? I'm seeing 600W PSW inverters in the $100 ballpark


 
The front end of an AC/DC brick like a small "wall wart" that would power a small piece of electronics usually looks like this:

1615268462335.png

This kind of circuit really doesn't care if it's a sine wave or modified sine wave as the first thing it's doing is removing the AC content with the rectifier and filter; then following it up with a regulator. You could power it with a square wave and you would still get some power through the transformer + rectifier, (and I encourage some enthusiastic signal-generator-owner to demonstrate this for us).

As electronics get bigger and more expensive, they start to have more elaborate front-end circuits like isolated flyback converters. Laptop chargers for example have more elaborate AC/DC converters since they are trying to be more efficient. But a brick like might power your WiFi router or similar won't care about modified sine vs pure sine.
 
You're showing an old-fashioned wall wart with 50Hz (or 60Hz) step-down transformer. Heavy and low power. Plus a linear regulator output.

The universal ones now made skip that transformer and rectify into a 400V cap. Then they chop at high frequency into a small transformer, with feedback to regulate. Saves money, and works at both 120V and 240V.

The one you're drawn might get warm with the higher frequencies of MSW into its core.
With sine wave in as intended, of course the current out isn't such a pretty waveform either. Maybe that causes heating from harmonics just the same, I'm not sure.
 
I haven't spent much time searching for such an item, but with most laptops moving to USB-C for power delivery (maybe not gaming laptops though), I wonder if there is an off-the-shelf DC-powered USB-C charger available.

A roundabout way would be a POE adapter like this; maybe suitable if you want to locate the POE injection device near the battery and the laptop at the other end of a long ethernet cable. POE is approx 44-48V so can probably be done with just a buck regulator if you have a 48V battery.
 
The universal ones now made skip that transformer and rectify into a 400V cap. Then they chop at high frequency into a small transformer, with feedback to regulate
This is the flyback converter I mentioned. The point is still valid though: once you've done the rectification, it doesn't really matter what sine / non-sine you used to generate the rectified DC voltage.
 
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This kind of circuit really doesn't care if it's a sine wave or modified sine wave as the first thing it's doing is removing the AC content with the rectifier and filter; then following it up with a regulator. You could power it with a square wave and you would still get some power through the transformer + rectifier, (and I encourage some enthusiastic signal-generator-owner to demonstrate this for us).

That is not really true. The steps in a modified sine wave are rather difficult on the the front-end components and create a ton of noise that can go beyond the Power Supply Rejection Ratio. The high current and voltage steps along with the noise that bothers the extremely fragile control loops ultimately end up as noise inside your device. Some devices are more sensitive than others. In general, the lifespan of the AC to DC supply is diminished.

I design and build power commercial power electronics and do not allow any modified sine wave inverters to be used at all to feed my products.

They will not instantly blow stuff up, but the out of sight problems are not worth it for me.
 
go beyond the Power Supply Rejection Ratio
This phrase makes no sense. The PSRR is the attenuation factor from power supply to some node, such as the regulated output. There is no such thing as "going beyond it". Source: I have an advanced degree in analog circuit design and work in this area.

But yeah in general I agree with the spirit of your comment: you're right that there is more interference from a modified sine inverter. My point is that for a simple transformer / rectifier front end like you might find in a small AC/DC block, the simplest example schematic I could find, it's not a problem. If it was, then why do we see so many people using modified sine inverters without issue? Why are they even available for sale? It's a non-issue for most electronics, and yes it definitely has the potential to be an issue for others, depending on their power supply design.
 
The cost difference between a modified and a true sine wave is slight. I only ran electronics off a modified sine wave generator because that was what Amazon had in stock for 2 day delivery approximately 3 days before the hurricane. If you have the luxury of time and the choice, get sine wave. If not, generally not a big problem.
 
This phrase makes no sense. The PSRR is the attenuation factor from power supply to some node, such as the regulated output. There is no such thing as "going beyond it". Source: I have an advanced degree in analog circuit design and work in this area.

But yeah in general I agree with the spirit of your comment: you're right that there is more interference from a modified sine inverter. My point is that for a simple transformer / rectifier front end like you might find in a small AC/DC block, the simplest example schematic I could find, it's not a problem. If it was, then why do we see so many people using modified sine inverters without issue? Why are they even available for sale? It's a non-issue for most electronics, and yes it definitely has the potential to be an issue for others, depending on their power supply design.

The PSRR describes how a signal on the DC input voltage of the regulator system is transmitted to the regulated output.
I am not making this up. How much noise on the input vs noise on the output. How much noise the power supply can reject.

A power supply will attenuate noise by some db's/frequency and whatever is left over it the noise that 'goes beyond' the ability of the supply to reject it. What am I missing?

1615326368550.png
I totally agree that modified sine inverters are just fine for a lot of things. My problem is that they are not fine for all things. After an inverter is installed and it appears as a regular outlet - the end user is not going to do any analysis of whether or not it is a good idea.

With a sine wave inverter, anything you can plug in is fine - whether it is some delicate analog device or a light bulb.
 
The cost difference between a modified and a true sine wave is slight. I only ran electronics off a modified sine wave generator because that was what Amazon had in stock for 2 day delivery approximately 3 days before the hurricane. If you have the luxury of time and the choice, get sine wave. If not, generally not a big problem.

The price difference is indeed rather small - IMHO the modest additional cost of sine wave is worth not needing to worry.
 
A power supply will attenuate noise by some db's/frequency and whatever is left over it the noise that 'goes beyond' the ability of the supply to reject it. What am I missing?
I think your misunderstanding, or at least given how you have worded it both times, is that the PSRR is some threshold below which the interference is fine and above which it is not fine. This is not the case. It is a multiplicative factor; and based on small signal / linear approximations: ripple on the power supply gets attenuated by the PSRR and appears on the node you're talking about. How much ripple that node (or any node) can tolerate is a completely separate issue and has nothing to do with the PSRR. For example: is that node the sensing electrode for an EKG? Then it can't handle much interference. Or, is it just an input to some secondary voltage regulator? Then it can handle more. I hope that makes sense; maybe you already get it and are just describing it weirdly.
 
I hope that makes sense; maybe you already get it and are just describing it weirdly.
Fair enough....my wife says the same thing.

And no - it is not a threshold. That is why I noted it is expressed in db at a certain frequency - not any fixed threshold. The load will have a certain amount of noise at various frequencies that are considered tolerable. That is different with from device to device and no way to boil it down to any specific threshold.....that is not what I was trying to do. I thought I was being rather clear, but perhaps making assumptions.

The point is that modified sine is noisy. In some cases very noisy. There are some devices that cannot tolerate that for various reasons. Therefore - I recommend sine wave for everything since it has no corner cases of devices that will not work or otherwise be compromised.
 
To the extent magnetics are involved, PSRR probably isn't linear.
A choke can only choke so much before it can't choke any more.
Most dramatic with common-mode chokes, which are probably limited mostly by resistance heating. A (tiny) 5A common-mode choke carries differential current with little or no magnetic field generated. Small amounts of common-mode can be blocked. But it only takes about 50 mA of common-mode current to saturate the choke and it doesn't do anything any more.

A choke could be tested with DC bias, if your analyzer has bias Tees. For a common-mode choke, I measured impedance of one coil while pushing a DC current through the other, and found where it began to saturate. Confirming figures like above, which weren't given for the particular part on hand but I anticipated because a different brand listed common as well as differential saturation current.

Modified Square Wave will have huge harmonics (differential) and any single-ended chokes trying to block them might be over driven.

But as soon as any power supply rectifies a sine wave into a capacitor, it makes its own harmonics.
 
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