Welcome, Guest. Please login or register. Did you miss your activation email? This topic This board Entire forum Google Bing. Print Search. I have a floating power supply; this means that it has two output lugs positive and common.
It does not have negative voltage output becaz I tend not to work with negative voltages as much. That would give me true 0V reference. That is generally fine. Your idea of a "true 0V reference" isn't really possible.
Voltage is simply a measure of different potentials between two points.
Ground or 0V is whatever you define it as. Earth ground doesn't have to be though of as 0V. If you define your positive output as 0V, then you indeed have a negative output power supply. If the power supply is properly floating, you could tie this output to ground and make the negative be a voltage below ground.
All of it is based on what you set as the reference point. Please see the attached schematic. Would doing so help the accuracy of the power supply?
US2895059A - Floating power supply circuit - Google Patents
You can connect the common to mains earth, but do you actually want to? We don't know what you are going to use the supply for, so it is hard to give advice. There is a good reason why power supplies usually have a floating supply and a separate earth terminal that you can connect if you choose.
Not earthing the supply may be important if you need to connect it to a circuit that cannot have the 0V earth. For example, if you need to use it as a negative supply with the positive rail earthed, or if you want to put it in series with another supply to increase the voltage.
If you want to keep the option open, leave the mains earth as a separate terminal. A second reason is earth loops can cause measurement problems, so there are times when you need to be able to control the earth on the circuit at the load rather then having multiple earth connections through the power supply, oscilloscope, etc.
A third reason is at times, you might need to connect an oscilloscope between two points of the load that are not connected to the negative rail. You can do this with an isolated supply, but you cannot with an earthed supply.
If none of the above matter, then there is probably no reason not to connect the negative supply rail to mains earth. What's the exact way of paralleling floating supplies? And in series. Did a google search and no relevant images came up.
Except This Statement. Quote from: amspire on April 12,am. Quote from: ejeffrey on April 12,am. There was an error while thanking. SMF 2. EEVblog on Youtube.Compared to TN systems or TT systems "grounded systems"the IT system "ungrounded system" is a system type that is rarely used, even though in many cases it would be the better alternative.
Why do we then settle for worse alternatives in practice? The answer appears to be the following: habit, convenience, ignorance. The floating system is not very well known in the field. In fact, this topic is barely touched upon in universities and during apprenticeships. As a result, the grounded system has been established as standard and continues to spread. The IT system is rarely used and when it is, it is mostly in applications where its advantages cannot be waived.
This is the case in, for instance, operating theaters and intensive care units or in railway signalling technology. Because here, human lives are at stake. But isn't it always about human lives in power supply systems? The main difference between the IT system and the TN or TT system is a conductive connection between the star point of the transformer which supplies the system and ground. This connection exists in the grounded system, but not in the ungrounded system.
What is the big difference regarding the impact if there is only such a small difference in the implementation? Because a current does flow but it is very small since it depends on leakage capacitances and the enclosure is grounded. What is this like in a grounded system? Here, we set up a closed circuit in advance and then, to a certain degree, just wait for the fault.
If in this case a person touches a live conductive enclosure, without an overcurrent protective device a fault current would immediately flow through the person due to the low-resistance connection to the supply transformer. To ensure that the required protective measures function at this moment, it must be tested at regular intervals.
But how often are these tests actually carried out? For this purpose, devices for stationary installation and mobile devices are available. In principle, fault location is also possible in grounded systems using ground-fault monitoring RCM technology. However, with the restriction that this technology only works in energized systems and, unlike IT systems, remains restricted to asymmetrical ground faults.
If a ground fault or even a dead ground fault occurs in an ungrounded system, shutdown is not necessary. This is also the reason why floating systems are mandatory, e. In the event of a ground fault, the supply to life-supporting equipment is maintained. The IT system is in general perfectly suitable for all applications in which shutdowns are unwanted, would have serious consequences or would cause high costs — in the process industry, in data centers, in automation, basically everywhere.
Control circuits of all types are of particular importance. Controller errors and failures in control circuits — e. Based on the information provided by the ground-fault monitoring device it is possible to plan long-term servicing and maintenance work in the floating system and avoid unplanned service calls to rectify malfunctions. Another crucial advantage is that deteriorations of the insulation level can be detected immediately.
In a grounded system, fault currents can be resolved in the single-digit milliamp range by means of sophisticated ground-fault monitoring RCM technology — but no further. This is a significant improvement compared to a grounded system not being monitored that unexpectedly shuts down. It is even possible to measure in the megaohm range and above — which implies a factor of at least 1, compared to the grounded system.
Therefore, insulation deteriorations in an ungrounded system can be measured and rectified much earlier. In an IT system, symmetrical faults can be detected via an active measuring ground-fault monitoring device. Symmetrical faults are insulation deteriorations of a similar magnitude on all line conductors.
Such faults are quite common. For example, the insulation values in photovoltaic systems often deteriorate to a similar degree on the positive and the negative side. Instead either residual current monitors RCM with a DC supply voltage can be used or an IT system with ground-fault monitoring can be implemented.
DC fault currents may occur if there are battery systems, converters, switched-mode power supplies etc.Bell, Monrovia, Calif. Cl This invention relates to Where the output of a fullwave rectifier has to operate into a load which is not grounded, or which is tied to ground by a very high impedance, objectionable ripple currents may be present which cannot be filtered out by ordinary techniques.
For example, if a large capacitor is provided to bypass the ripple of currents to ground, it could produce an undesirably long time response to transients produced by switching of loads, or the like. The present invention provides a rectifier power supply having an output which is floating with respect to ground, and yet provides a very low ripple voltage without the use of large bypassing condensers to ground.
To this end, the present invention provides a circuit including a conventional fullwave rectifier with filter operating into a useful load. In addition, a second fullwave rectifier of opposite output polarity with a dummyload is connected to the same transformer. This second rectifier and load has no useful purpose other than to make the transformer circuit symmetrical. As a result the ripple currents to ground are balanced out, as will hereinafter become more apparent.
For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:. Referring to Fig. A transformer having balanced type construction is desirable to minimize ripple currents due to secondary capacity unbalance to ground of the secondary winding of the power transformer. A pair of diodes 12 and 14 connect opposite ends of the secondary of the transformer 10 to a common output lead The resistors 1S and 20 may be provided in series with the diodes 12 and 14 for current limiting purposes.
A conventional RC circuit, as indicated generally at 22, may be provided for filtering the output of the fullwave rectifier provided by the diodes 12 and The input to the filter 22 is connected between the center tap of the secondary of the transformer 10 and the common output lead Voltage regulation may be provided by a Zener diode 24 connected across the output of the filter 22 for maintaining the output voltage fixed over a large range of load changes on the output.
The circuit as thus far described comprises a conventional fullwave rectifier with the output floating with respect to ground. A resistor R shown dotted in the figure, indicates a high impedance current path to ground at the output of the power supply. Patented July 14, the equivalent circuit of the power transformer is shown, which includes distributed capacity to ground, as indicated by the capacitors 24 and 26, the secondary of the transformer 10 also includes in addition to the mutual inductance of the windings 28 and 30, leakage inductance indicated at 32 and 34, and D.
Thus the voltage E on the initial positive halfcycle as shown, does not reach the open circuit voltage indicatedby the dotted line, but is reduced in amplitude by the amount of the voltage drop across the leakage resistance On the non-conductive halfcycle, the voltage E reaches its open circuit value.
Similarly, the voltage E across the other half of the secondary on its non-conductive halfcycle reaches its full open circuit voltage, but on its conductive halfcycle it is reduced by the IR drop in the leakage resistance. The resulting ripple voltage V appearing across the high resistance to ground is shown in Fig. This voltage swing V in the center point of the secondary can best be appreciated by the equivalent circuit of Fig.Buoys Marker BuoysMooring Buoys.
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Dock Flotation. Floating Dock Hardware. Aluminum Gangways. Fish Cleaning Tables. Dock Bumpers.First let me tell you that a floating power supply output is NOT what is shown below in Figure 1 haha. As long as that is true, the person can freely touch things without the risk of getting shocked due to two of the things he touches at the same time being at different voltage potentials, or one of the things being at a high voltage potential with respect to the earth.
If the voltage difference is high enough, the person could be shocked. Earth grounding the chassis also protects the user if there is an internal problem with an electrical device causing its chassis to inadvertently come in contact with an internal high voltage wire. Since the chassis is earth grounded, an internal short to the chassis is really a short to ground and will blow a fuse or trip a circuit breaker to protect the user instead of putting the chassis at the high voltage.
If you touched a chassis that had a high voltage with respect to ground on it, your body completes the path to ground and you get shocked! So to protect the user and for some other reasonsthe chassis of Agilent power supplies are grounded internally through the ground wire the third wire in the AC input line cord. Additionally, most if not all of our Agilent power supplies have isolated floating outputs.
That means that neither the positive output terminal nor the negative output terminal is connected to earth chassis ground. See Figure 2. For floating DC power supplies, the voltage potential appears from the positive output terminal to the negative output terminal. There is no voltage potential at least, none with any power behind it from either the positive terminal to earth ground or from the negative output terminal to earth ground. A power supply with a floating output is more flexible since, if desired, either the positive or negative terminal or neither can be connected to earth ground.
Some devices under test DUT have a DC input with either the positive or negative input terminal connected to earth ground. If one of the power supply outputs was also internally connected to earth ground, when connected to the DUT, it could short out the power supply output. So power supplies with floating output terminals no connections to earth ground are more versatile. If the outputs are floating from earth ground, we need to specify how far above or below earth ground you can float the output terminals.
Our power supply documentation provides this information. You will frequently see the following in our documentation:. Also, some power supplies have different float ratings for the positive and negative output terminals. Figure 4 shows an example of floating a power supply to V above ground. The power supply output is set to 40 V.
How do you decide when one must have an earth connection or not. Zoom in on the schematic, and you will see that the ground on the left side of the transformer is labeled "Vpri", and on the right side "GND". Vpri isn't tied to any particular ground at all. It's shown with a ground symbol only because it is used as the reference for all other voltages on the primary side of the transformer.
Since Vpri is tied to the negative side of the full wave bridge rectifying the incoming AC, it will be at the negative peak voltage of the AC part of the time. This is relative to something outside this circuit. That would be a dangerous voltage for a user to touch. However, it doesn't matter since nothing on the primary side of the transformer is accessible other than the wall plug. Everything else stays internal to the case of the supply, so it can be at dangerous voltages without harm.
The ground of the secondary side is meant to be connected to externally. However, this is isolated from the line voltages on the primary side by the insulation in the tranformer.
That's a valid and safe way of isolating the user from the dangerous voltages on the primary side. Such devices would need to pass something known as a "Hi-pot" test during manufacturing.
The tie the two AC inputs together, and deliberately apply several times the expect max voltage between there and the output GND. There may only be some very minimum leakage to pass, usually in the micro-Amp range. Hi-pot test voltages are usually in the 1. There is no need to "convert" this circuit from non-floating to floating, because it already is floating.
This circuit is not a nice example as it uses the same symbol for input primary ground and output ground. Only when you zoom in do you see that it has 2 grounds. You talk about floating which would suggest that the primary ground is "floating" but it is not really floating, it is mains connected and unsafe to touch. Look at the designs with a mains earth input, it will basically be the same circuit where the output ground is often connected to the mains earth.
What to choose depends on the user case. If a mains earth is expected to be present then it would be a good idea to use it. The "floating" ground supplies will often have their output floating at around half the mains voltage because there is no ground reference.Most electrical circuits have a ground which is electrically connected to the Earthhence the name "ground".
The ground is said to be floating when this connection does not exist. Conductors are also described as having a floating voltage if they are not connected electrically to another non-floating grounded conductor. Without such a connection, voltages and current flows are induced by electromagnetic fields or charge accumulation within the conductor rather than being due to the usual external potential difference of a power source.
Electrical equipment may be designed with a floating ground for one of several reasons. One is safety. For example, a low voltage DC power supply, such as a mobile phone charger is connected to the mains through a transformer of one type or another, and there is no direct electrical connection between the current return path on the low-voltage side and physical ground earth.
Ensuring that there is no electrical connection between mains voltage and the low-voltage plug makes it much easier to guarantee safety of the supply. It also allows the charger to safely only connect to live and neutral, which allows a two-prong plug in countries where this is relevant. Indeed, any home appliance with a two-prong plug must have a floating ground.
Another application is in electronic test equipment. Suppose you wish to measure a 0. If the whole device floats, then its electronics will only see the 0. Such devices are often battery powered. Thirdly, a floating ground can help eliminate ground loopswhich reduces the noise coupled to the system. An example of such a configuration is shown in the image on the right.
Systems isolated in this manner can and do drift in potential and if the transformer is capable of supplying much power, they can be dangerous.
This is particularly likely if the floated system is near high voltage power lines. Floating grounds can be dangerous if they are caused by failure to properly ground equipment that was designed to require grounding, because the chassis can be at a very different potential from that of any nearby organisms, who then get an electric shock upon touching it. Live chassis TVs, where the set's ground is derived by rectifying live mains, were common until the s. Exposed live grounds are dangerous.What is FLOATING GROUND? What does FLOATING GROUND mean? FLOATING GROUND meaning & explanation
They are live, and can electrocute end users if touched.