Usb 5v 500ma что это
5V 500mA USB charger US plug
- Input: AC 100-220V 50-60Hz 0.1A
- Output: DC 5V 500mA
- Output Interface: USB Output
This is a cheap charger and it arrived in a plastic bag inside a envelope.
- Power consumption when idle is 0.17 Watt
- USB output is coded as Apple 1A
- Weight: 20g
- Size: 66.0 x 37.6 x 14.5 mm
The 0.5A rating is a bit on the high side when the charger is run from 120VAC. It is more like 0.4A.
The voltage is on the high side.
At 230VAC it can deliver 0.7A, but the plug is for 120VAC.
I did the one hour test at 230VAC with 0.5A current and it could do that.
The temperature photos below are taken between 30 minutes and 60 minutes into the one hour test.
HS1: 57.9�C
The hottest part in the charger is the transformer.
M1: 44.9�C, HS1: 47.4�C
M1: 41.1�C, HS1: 44.2�C
M1: 43.1�C, HS1: 49.3�C
M1: 35.5�C, HS1: 57.9�C
M1 is probably the rectifier that shows up, but it is not really warm.
At 0.5A the noise is 40mV rms and 392mVpp.
After using my vice to crack the glue I could open it with a spudger.
In this side is a fusible resistor (R1) at the input, a transistor to handle the mains switching (Q1), a optocoupler with a zener diode at the low volt side. The rectification is a diode (D3).
This side has the bridge rectifier and the second transistor (Q2) in a two transistor mains switcher. The coding resistors (R7..R10) for USB output is placed below the USB connector.
The distance between mains and low volt side is about 4.5mm, this is considerable lower then the legal requirement.
Testing with 2830 volt and 4242 volt between mains and low volt side, did not show any safety problems.
I like the enclosure of the charger it looks nice, but that do not really help it. The output power is way to low and using a old type 1A coding for 0.5A charger is not very nice. The charger passes the high voltage test, but the creepage distance is too low, I also doubt the isolation in the transformer.
What is the power output of a USB port?
As the title says, what’s the power output of a USB port?
Is it a standard value, or it may change depending on manufacturer/model, and so on?
If that value is not standard, how can one determine it?
6 Answers 6
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.
A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
As power is equal to current times voltage, all you have to do is multiply 5V with the current the device is drawing from the port.
Note there also exists a convention for charging devices. These kinds of ports allow for currents up to 1.5 A (also using 5V). However, the USB port is rated to withstand current up to 5 A—so some manufacturers may go out of spec and offer a higher maximum current.
There are USB power adapters on the market explicitly stating «10W adapter». As USB is 5V the 10W result in 2A = 2000 mA. The net effect is that devices connected to this adapter charges its battery 4 times faster than with a «normal» 500 mA USB port.
Power that must be delivered by a USB port is defined in Section 7.2.1 of USB 2.0 Specifications.
To start, the power delivery is defined in «units of load». For USB 2.0 one unit is 100 mA, and for USB 3.x one unit is 150 mA.
USB standard defines two classes of USB ports, «high-power ports», and «low-power ports»
The specs says, page 171:
«Systems that obtain operating power externally, either AC or DC, must supply at least five unit loads to each port. Such ports are called high-power ports.»
So, if you have a desktop PC or laptop connected to AC outlet, each USB port MUST supply 500 or 900 mA of current. Note the language, «at least». So it could be more, unless an OPTIONAL overcurrent functionality is supported in hardware. For example, a common desktop PC in sleep mode derives the VBUS power from +5VSB rail of its PSU, which at least is capable to deliver 2 A of current. Or more, which is specified in particular PSU.
For example, if a Raspberry Pi3 gadget gets its power from AC-DC adapter from a wall AC power, it must supply at least 500 mA per each (of 4) ports. Unfortunately, it fails to do so, and therefore is not USB-compliant.
However, if a USB host is a skinny battery-powered device (such as MP3 player or smartphone), this can be declared by manufacturer as «low-power host», and the USB port can be limited by design to deliver 100/150 mA only. This limit is very inconvenient to customers, and is rarely enforced.
If a USB system (host or hub) is declared as normal host, the ports are tested to USB-IF test specifications using specialized USB port testers. The tester either applies a load equal to 5 units and checks if the voltage drop doesn’t exceed specifications (5% or 10% margin), or applies a step-wise increasing load and determines at which point the (optional) overcurrent circuit trips over.
Under household conditions the port capability can be checked by applying a big 10 Ohm (or 5.5 Ohm if USB 3.x) resistor to a stripped-off cable. Or using a dedicated variable load found on e-Bay.
The requirements for power delivery from a normal USB port should not be confused with requirements for USB DEVICES: USB devices should NOT take more than one unit of load until host completes the device enumeration. USB hosts must keep track of consumed power declared by attached devices. During enumeration a host reads mandatory power requirements of the device within its descriptor, and if the host believes that its power capabilities are maxed out, it can refuse the connection.
BU-411: Charging from a USB Port
The Universal Serial Bus (USB) was introduced in 1996 and has since become one of the most widespread and convenient interfaces for electronic devices. Compaq, DEC, IBM, Intel, NEC and Nortel contributed to the developments with the goal of simplifying the interconnection of peripheral devices to a PC, as well as to allow a greater data transfer rate than was feasible with earlier interfaces. The USB port can also be used to charge personal devices, but with a current limit of 500mA on the original design, this might have been an afterthought.
A typical USB network consists of a host that is often a PC and peripherals such as a printer, smartphone or camera. Data streams in both directions but the power is unidirectional and always flows from the host to the device. The host cannot take power from an outside source.
With 5V and 500mA available on version USB 1.0 and 2.0, and 900mA on USB 3.0, the USB can charge a small single-cell Li-ion pack. There is, however, a danger of overloading a USB hub when attaching too many gadgets. Charging a device that draws 500mA connected together with other loads will exceed the port’s current limit, leading to a voltage drop and a possible system failure. To prevent overload, some hosts include current-limiting circuits that shut down the supply when overdrawn.
The original USB port can only charge a small single-cell Li-ion battery. Charging a 3.6V pack begins by applying a constant current to a voltage peak of 4.20V/cell, at which point the voltage peaks and the current begins to taper off. (See BU-409: Charging Lithium-ion) Due to the voltage drop in the cable and connectors, which is about 350mV, as well as losses in the charging circuit, the 5V supply may not be high enough to fully charge the battery. This is a minor problem; the battery will only charge to about 70 percent state-of-charge and deliver a slightly shorter runtime than with a fully saturated charge. The advantage: Li-ion will last longer if not fully charged.
Standard A and B USB plugs, as illustrated in Figure 1, feature four pins and a shield. Pin 1 delivers +5VDC and pin 4 forms the ground that also connects to the shield. The two shorter pins, 2 and 3, are marked D- and D+ and carry data. When charging a battery, these pins have no other function than to negotiate current.
Figure 1: Pin configuration of standard A and standard B USB connectors, viewed from the mating end of the plugs
Pin 1 carries +5VDC (red wire) and 4 is ground (black wire). The housing connects to the ground and provides shielding. Pin 2 (D-, white wire) and pin 3 (D+, green wire) carry data
Besides the standard type-A and type-B configurations with 4 pins, there are also the USB Mini-A, Mini-B, Micro-A and Micro-B that include an ID pin to permit detection of which cable end is plugged in. The outer pin-1 is positive and pin-4 is negative. USB cables are generally standard type-A on one end and either type-B, Mini-B or Micro-B on the other. The new type-C connector described later features 24 pins and runs on the USB 3.1 standard.
Power Delivery
USB 2.0 with a current of 500mA has limitations when charging a larger smartphone or tablet battery. Keeping the smartphone running on a bright screen during charge could result in a net discharge of the battery as the USB cannot satisfy both. Connecting a high-speed disk drive requires more than 500mA and this can create a power issue with the original USB port.
In 2008, USB 3.0 relieved the power shortage by upping the current to 900mA. This current ceiling was chosen to prevent the thin ground wire from interfering with high-speed data transfer when drawing a full load.
With the need for more power, the USB Implementers Forum released the Battery Charging Specification in 2007 that enables a faster way to charge off a USB host. This led to the dedicated charger port (DCP) serving as a USB charger, delivering currents of 1,500mA and higher by connecting the DCP to an AC outlet or a vehicle. To activate the DCP, the D- and D+ pins are internally connected by a resistor of 200 ohms or less. This distinguishes the DCP from the original USB ports that carry data. Some Apple products limit the charge current by connecting different resistor values to the D+ and D- pins.
To support charging and data communication when using the DCP, a Y-shaped cable is offered that connects to the original USB port for data streaming and to the DCP port to satisfy charging needs. This appears like a logical solution but the USB compliance specification states that the “use of a Y-cable is prohibited on any USB peripheral,” meaning that “if a USB peripheral requires more power than allowed by the USB specification to which it is designed, then it must be self-powered.” The Y-cables and the so-called accessory charging adapters (ACA) are being used without apparent difficulties.
The question is asked: “Can I cause damage by plugging my device into a USB charger that delivers more current than 500mA and 900mA?” The answer is no. The device only draws what it requires and no more. An analogy is plugging in a lamp or a toaster into an AC wall plug. The lamp requires little current while the toaster goes to the maximum. More power from the USB charger will shorten the charge time.
Sleep-and-charge Mode
In most cases, turning the computer off also shuts down the USB. Some PCs feature the sleep-and-charge USB port that remains powered on and can be used to charge electronic devices when the computer is off. Sleep-and-charge USB ports might be colored in red or yellow, but no standard exists. Dell adds a lightning bolt icon and calls it the “PowerShare” while Toshiba uses the term “USB Sleep-and-Charge.” The sleep-and-charge USB ports may also be marked with the acronym USB over the drawing of a battery.
USB 3.1 – Type-C Connector
As with most other successful technologies, USB has spawned several versions of connectors and cables over the years. USB chargers do not always work as advertised and charge times are slow. Incompatibilities between competitive systems exist, willingly or by oversight.
Companies overseeing USB standards are aware of the shortcomings and brought out the type-C connector and cable based on the USB 3.1 standard. Rather than using four-pins as in the classic type-A and type-B, the type-C connector has 24 pins and is reversible, meaning it can be plugged in either way. It supports 900mA and, on command, delivers 1.5A and 3.0A over a 5V power bus while streaming data. This results in 7.5 and 15 watt power consumption respectively, as opposed to 2.5W using the original USB (current times voltage = wattage). The type-C can go up to 5A at 12V or 20V, providing 60W and 100W respectively. Figure 2 shows the pinout of the USB Type-C connector.
Figure 2: Pin configuration of USB Type-C connector
Side A and B are mirror images. Some pins are connected in parallel to gain higher power and more reliable connections.
New devices come with the USB-C connector and USB 3.1, but consumers beg for two or three regular USB 3.0 ports on their gadgets to support what worked so well in the past. USB 3.1 is backward compatible with USB 2.0 and USB 3.0 and the classic type-A and type-B connectors. While in transition to the type-C, adaptors are available to convert, but expect lower data transfer speeds with adapters than what USB 3.1 offers.
With the availability of higher currents and voltages on the Type-C system as compared to the Standard A and B connectors, damage to a device can be afflicted when giving a wrong digital command. The commands may come from a device or an adapter requesting modified power demands. It is advised to only use compatible or trustworthy brands when experimenting with higher voltages and currents in USB connectors.
Project: “Generic” USB 5V/500mA Charger Kit
When it comes to power supplies, the standardisation of USB has made it the ubiquitous choice for many mobile and portable devices. As a result, you probably have an abundance of spare USB power supplies to charge or power your devices with … except that maybe you don’t.
The amount of new products that don’t come with power supplies of their own, in order to cut costs, has been rather disappointing and can result in strange compatibility issues such as slow charging (due to incompatible signalling) or instability due to poor power quality.
So maybe you are after a USB power supply … then you come across a DIY kit to build one for just AU$2.35 including postage … is it a good idea to just build one?
The Kit
For this particular kit, there is no zip-lock bag – just a regular plastic bag closed with some adhesive tape.
Inside, there is a casing, although curiously, it seems to have been adapted from a Li-Ion charger design of sorts, claiming 4.2V/500mA in the molding, model JY-500. There is a pre-wound transformer, some capacitors, resistors, diodes, transistors, a bi-colour LED, opto-isolator and USB socket.
The PCB is somewhat rough around the edges, of a fibreglass variety with silkscreen printing on the top. The only identifiers seem to be H15061502, suggesting to me, possibly a design on the 15th June 2015? The drill-holes also seem to have torn the substrate slightly resulting in the white-halo around the holes.
The underside is a solder-masked copper pattern with lacquer, not the easiest type of board to solder to. Isolation between primary and secondary is visible, and seemingly sufficient assuming the kit is properly constructed. Knowing what I’m like, I probably wouldn’t trust myself to do it right …
The kit comes with a double-sided page of information including a schematic, layout and bill-of-materials. It seems that it’s based on a self-oscillating design with a primary and feedback winding, with this oscillation inhibited (?) by feedback from the secondary when a Zener diode indicates over-voltage. The circuit doesn’t have much in the way of output filtering – notably absent are any inductors for a tuned filter … I don’t think this is a great design. There aren’t any fuses on-board either … with the input appearing to be half-wave rectified as well, which wouldn’t make the power company too happy either.
Construction
A quick computation on the number of joints to complete the kit:
Overall, construction is straightforward – populate and solder with everything being through-hole. One little trick that caught me was the white dot next to the optoisolator on the silkscreen – this does not indicate Pin 1. Mounting the opto-isolator in reverse (as I did initially) results in unregulated output of about 15V (. ) which can damage devices. The other is the LED – which I mounted in reverse. I suspect F indicates flat … but since it’s a bi-colour LED, this just results in inverted colour indication.
The underside of the board – it’s good to make sure there’s no stray scraps of solder or anything bridging primary to secondary for your own safety.
Trim off excess wire and tin the ends. Then using a hefty iron, heat the pins just enough to get solder to take and then solder the wires to the pins. Overheating will result in the pins migrating through the case.
The case snaps together and is secured with a single screw. When constructed, it looks as follows – almost indistinguishable from the cheap and dangerous bricks often found with cheap Chinese equipment. Notice the strange pre-moulded ratings which refer to a Li-Ion charger of some sort.
The USB connector nestles nicely into the side cut-out.
Assuming you left a little excess length on the LED legs, it comes through the casing quite nicely like so.
Testing
Assuming you’ve been able to find an appropriate adapter so that you can plug the unit into mains (the one I used is a cheap one from China), you should test the output with a USB charger doctor that you don’t care too much about. The reason I say this is because if you reversed the optoisolator (as I did initially), you would have an unregulated output of about 15V that could fry attached devices.
Then, in theory, you could probably connect a load onto it and use it. Note how the charger doctor seems to claim my power bank which is charging is drawing 420mA and having a 4.78V output? Well that’s not quite all fine and dandy …
Getting out the heavy test equipment tells us the bigger picture:
When the charger is idle, it consumes about 113mW, which is below the 1W limit, but it’s still about five to ten times greater than most high-quality supplies included with mobile phones today. The high consumption is possibly down to the LED power consumption and the quality of the transformer itself.
The no-load ripple, however, is rather shocking being about 631mV (!!). Most factory chargers don’t put out more than about 120mV under load, so this is high enough potentially to cause malfunctions or stress on components.
Putting my B&K Precision Model 8600 DC-load to work in constant current mode, I found that the voltage collapsed very quickly at 500mA, so dialling it back to 420mA, we can see the voltage waveform rides from about 5.3V down to 3.9V, the measured ripple averaging about 1.445V. This is the sort of output we might expect from a heavy linear brick supply. Not good.
Worse still, it seems the supply could not withstand even that, folding back its output voltage as it warmed up, resulting in reduced power delivery even at 400mA (above).
It seemed to stabilise more at 350mA, sticking to a nearly healthy 5.20V output. But using 3.62W to generate 1.82W output tells us the supply is merely 50% efficient – a far cry from the 80%+ we’re commonly seeing on quality supplies.
Conclusion
While this kit is inexpensive and comes with a nice enclosure, it’s not a kit I would recommend to newcomers, or for those who actually want a decent USB power supply of any sort.
Being a mains-powered device comes with inherent risks in case of incorrect construction. There is a good likelihood of a pop and some magic smoke, but also, in case of incorrect construction, isolation from the mains might not be guaranteed especially if you don’t assemble the case correctly or at all. For newcomers, I’d hazard to say that it’s not worth your life or various hazards to save a few bucks and have the chance to build your own charger … the plug isn’t even the right sort for Australia!
The PCB quality isn’t ideal for easy construction either, and soldering to the power pins requires a decently hefty iron. The isolation of the supplied transformer is not guaranteed either …
While I might sound somewhat negative, what really puts the nail in the coffin is its performance – the standby consumption is “acceptable” but slightly high possibly due to the LED, but the on-load efficiency is poor (50%) and sourcing anywhere more than about 350mA results in excessive ripple and inconsistent performance. It won’t charge anything quickly or smoothly … I’m pretty sure I won’t want my precious USB-powered devices being subjected to such “noisy” power. Not that this level of power is enough for many devices anymore …
That being said, this was what I expected from something advertised as a “500mA” charger – the bare minimum that could even be potentially useful. But it can’t even deliver on that claim … but at least I can say I built it …