Will an AC to DC converter work if the input was DC instead of AC?
Will an AC to DC converter work if the input was DC instead of AC?
If I were to take a standard AC to DC converter, say a laptop charger, and hook up the input side (which expects 120VAC at 60Hz) to a DC power supply of some sorts, will the electricity still be "converted," or will it just not work at all? I am clearly very uneducated when it comes to electronics (albeit working on it) so I would very much an ELI5 answer Thanks!
The way you get dc from ac is by using a full bridge rectifier that changes the negative peaks of ac into positive ones. If you where to put dc through it it should just pass like normal
Unless there is a transformer. Also, it may just catch fire depending on the input voltage
can someone explain this imagine?
Think about the circuit over time. The sine wave on the left is the input.
When the sine wave is positive, the top wire is positive and the bottom wire is negative. That means d1 and d3 are both positive and d2 and d4 are both negative.
Diodes "forward bias", meaning they allow electricity to flow, when you have a positive on the triangle side. This also implies a negative on the straight bar side. If the positive is on the straight bar side, then it won't conduct. You have to have a negative on the straight bar side.
Note: Keep in mind positive and negative means in relation to each value. So if one side is 5 volts, and the other is 0, then the other side is negative compared to the positive side.
So with that in mind, when the sine wave is positive, greater than 1,then d1 and d4 are conducting (there an implied loop on the left side).
When the sine wave is negative, then d2 and d3 are conducting. Because these two diodes are flipped, the high value goes to the top wire on the output which is now seen as a positive. The input is different, but because you've flipped the wires, the output is still the same. Now all current flows in one direction no matter the input. AC is now DC.
Shorter verison: positive side of the sine wave makes d1 and d4 conduct. Negative side makes d2 and d3 conduct. Since d2 and d3 cross over, they effectively turn the negative into a positive value.
Please excuse this attempt from a mere technician.
The waveform on the far left is the electrical signal fed into the rectifier. It illustrates a current that starts at zero, then reaches its full positive amplitude, then comes back to zero, then reaches the full negative, then back to zero. This represents an AC or alternating current. This is the way electricity comes out of your wall, usually.
DC or direct current is instead just a constant horizontal line. Ideally no change in the current. This is what we get from batteries and is used in most of our smaller devices like computers and smartphones. So naturally its handy to have a device that "adapts" the AC to DC. A common part of AC to DC Adapters is a rectifier.
The diagram in the center of the image is the schematic of a full bridge rectifier. It shows the two wires that feed into the rectifier on the left, these are then split into an arrangement of diodes represented by triangles with lines at their tips. Diodes essentially only allow current in one direction. The line is representative of a "direction" of the flow. The particular way these diodes are arranged means that no matter what kind of signal is fed in it will never produce a negative voltage at the output.
By using this arrangement we can feed in the AC signal and sort of flip the negative of part of that signal so the waveform looks like the one on the right. You can see that the waveform now is only above the line representing zero.
This is however only one step in the process of a power regulation and so as others have pointed out its not as simple as it may seem. Usually a transformer is used to step up or down voltages, and those are not designed to be used with DC and I believe could be damaged?
In most cases it will work fine as the first thing a good power supply does to the incoming electricity is converting the AC to DC using a full bridge rectifier. If you already supply DC, the current will just flow through it without a problem and the power supply simply continues to do its stuff.
However note that the DC input voltage needs to be relatively high. About sqrt(2)~=1.4 times as high as the rated AC voltage should be fine. So if you have a power adapter that's rated for 120 to 240 VAC, you should give it something between 170 and 340 VDC. This is obviously very high (and dangerous). Plugging in a normal car battery or the output of a usb charger or something like that will likely do nothing.
It depends! Most AC to DC converters actually convert from AC to DC back to AC (at a higher frequency) then to DC again. The higher frequency means you can use a much smaller and lighter transformer for the same power. Depending on how it does the first AC to DC step, you could be ok giving it DC, but I wouldn't do it unless the power supply says it's rated for it.
You could get an output, but if you want to take 100Vdc and turn it into 10Vdc.. it will not do this... for this you will need a buck, sepic, buck-boost, cùk, resonant, or some other converter..
In the case of the rectifier:
if you look at a simple AC to DC converter (half-wave rectifier) either output = 0 volts or output = input - conduction losses, depending on how you polarized the DC source.
In another circuit (full wave rectifier), the diodes will be polarized such at two will allow current flow. output = input - conduction losses
If the rectifier is something more complex (12 pulse rectifier).. this circuit relies on transformers. If you put DC on the primary of the transformer then the output will be 0 volts and thus the rectifier output will also be 0 volts. In this example I've ignored the fact that the transformers have 3 terminals and the DC source would only have 2.
I'm less knowledgeable of more elegant rectification methods (such as active rectification)...
Interestingly.. the fundamental DC to AC converter (inverter) is the same circuit as the full wave rectifier, with the diodes replaced with controllable switches (SCRs, IGBTs, IGCTs, MOSFETs, ect.)
It's actually very hard to predict without looking at the PSU. And depending on the design, the failure will be by shorting your DC current supply, so I really don't recommend testing it.
But many designs handle a DC supply perfectly fine.
Depends on how it works. I would expect that some would work but soon fail due to some components being overstressed, and others not to work at all.
I'm not an expert but as it is commonly explained, the first component of many (all?) switched mode power supplies (almost all laptop power bricks are SMPS) is a rectifier. If you feed a full bridge rectifier with DC, half of it will be unused while the other will carry all the current. The rest of the power supply after that should not care.
So in theory it should work, at least up to roughly half the rated load. But there may be other components like power factor correction circuits, safeties, or some details that those descriptions glossed over that make it not work.
Counterintuitively, if the device supports a wide voltage range (as many do) higher voltages may be better (as in less likely to fry it) as they require less current.
I think if a plug, or component, that's expecting alternating current input, gets direct current input -- it won't work.
But I'm super dumb, so I'm really interested now in the answer to this question.
It depends on the design of the power brick, but not something to try due to hazard, at the least could fry the adapter or at worst cause an electrical fire. There would be no reason other than, "here, hold my beer."
Some laptop adapters may use a bridge rectifier followed by a buck converter, but there's still plenty that use a transformer to step down AC voltage before presenting it to the rectifier-regulator. A transformer will become a toaster if DC voltage of any appreciable level is applied.
If the adapter happens to be one that does not use a transformer, a high enough DC voltage has to be applied with correct polarity. The voltage required would be output voltage plus "dropout" voltage of the buck converter. Dropout voltage could be pretty high so it can get into dangerous levels. If you managed it without electrocuting yourself or burning down your house, it could possibly output properly regulated voltage.
In reality, a practical application for DC-DC conversion is adapters for cigarette lighter sockets. I actually have one of those for my laptop. It steps up 12V DC from a cig lighter socket to the 19V DC plug for my laptop using something called a boost converter. USB cig lighter adapters are common and typically use a buck converter to step down 12V to the 5V of a USB plug.
No, in that case you will need a DC to DC converter. They work differently.
What makes it not work? Shouldn't the rectifier be happy with almost anything, and anything after the rectifier would be getting the same rectified voltage in either case?
That's kinda what I was thinking. Will anything be ruined in this case? What prevents it from working?
I would think it's because a "receiver" of AC current has to be specifically designed/set up to receive an alternating current. If it receives a direct current, it either doesn't know what to do with it, or it explodes.
Again though: I'm dumb, so please take my
opinionthoughts with a grain of salt.