Category: Reverse polarity dc circuit

Reverse polarity dc circuit

Batteries are most convenient power source to supply voltage to an electronic circuit. There are many other ways, to power up electronic devices, like adapter, solar cell etc but the most common DC power supply is Battery.

AC/DC: Understanding Polarity

So, in this situation Reverse Polarity Protection Circuit would be a useful addition to the circuit. Using a Diode is the easiest and cheapest method for Reverse Polarity Protection but it has a problem of power leakage.

When the input supply voltage is high a small voltage drop may no matter, especially when the current is low. But in case of low voltage operating system, even a small amount of voltage drop is unacceptable. As we know the voltage drop across a general purpose diode is 0. Be aware while choosing a Schottky diode, because lots of Schottky diodes comes with high reverse current leakage so make sure that you will choose one with low reverse current less than uA. You can even use a Full-bridge rectifier for reverse polarity protection, as it is regardless of polarity.

But bridge rectifier consists of four diodes, hence the amount of power waste will be twice of the power waste in the above circuit with single diode. Now, if the supply voltage is more than the Vgs then you have to drop the voltage between the gate terminal and source. Components required for making the circuit hardware is mentioned below. Now, when you connect the battery as per the circuit diagram, with correct polarity, it causes the transistor to turn ON and allows the current to flow through it.

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If the battery is connected backwards or in reverse polarity then the transistor turns OFF and your circuit gets protected. This protection circuit is more efficient than others.

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Formula for finding the voltage between gate and source is:. When the battery is connected incorrectlythe voltage at gate terminal will be positive and we know that P-Channel MOSFET only turns on when the voltage at gate terminal is negative minimum So, we can calculate the power loss in circuit like below:. So the power loss will be.

Hence, the power loss is about 27 times lesser than the circuit using single diode. It is little bit costlier than diode but it makes the protection circuit much safer and efficient. We have also used a Zener Diode and a resistor in the circuit for the protection against exceeding gate to source voltage. By adding the resistor and the Zener diode of 9. I think the.The terms "straight" and "reverse" polarity are used around the shop.

They may also be expressed as "electrode-negative" and "electrode-positive" polarity. The latter terms are more descriptive and will be used throughout this article. Polarity results from the fact that an electrical circuit has a negative and a positive pole. Direct current DC flows in one direction, resulting in a constant polarity.

Alternating current AC flows half the time in one direction and half the time in the other, changing its polarity times per second with hertz current.

A welder should know the meaning of polarity, and recognize what effect it has on the welding process. With few exceptions, electrode-positive reversed polarity results in deeper penetration. Electrode-negative straight polarity results in faster melt-off of the electrode and, therefore, faster deposition rate.

The effect of different chemicals in the covering may change this condition. Some types of shielded electrodes function on either polarity, though some operate on only one polarity. The use of the AC transformer-type welder necessitated the development of an electrode that would work on either polarity, due to the constant-changing of the polarity in the AC circuit.

Though AC itself has no polarity, when AC electrodes are used on DC they usually operate best on one specific polarity. The covering on the electrode designates which polarity is best and all manufacturers specify on the electrode container what polarity is recommended.

Reverse Polarity Protection Circuits

For proper penetration, uniform bead appearance, and good welding results, the correct polarity must be used when welding with any given metallic electrode. Incorrect polarity will cause poor penetration, irregular bead shape, excessive spatter, difficulty in controlling the arc, overheating, and rapid burning of the electrode.

Most machines are clearly marked as to what the terminals are, or how they can be set for either polarity. Some machines have a switch to change polarity, whereas on others it is necessary to change the cable terminals.

If there is any question as to whether or not the correct polarity is being used, or what polarity is set on the DC machine, there are two easily performed experiments that will tell you. The first is to use a DC carbon electrode, which will work correctly only on negative polarity.It is often useful to provide protection against accidental reverse polarity for your circuits.

This brief review will explore three simple methods for adding this protection to your projects. For a more in-depth tutorial, see this article. Diode Simply using a diode as shown in the first circuit is often a good approach.

The advantages are simplicity and cost. The disadvantages are larger power loss for larger circuit loads and a substantial voltage drop. Normal rectifier diodes typically drop around 0. If your circuit draws little power and can handle such a drop, then the blocking diode will work for you.

You can improve this circuit somewhat by using a Schottky diode.

reverse polarity dc circuit

It has a lower voltage drop - usually about 0. There is one potential problem with using Schottky's though. They have more reverse current leakage, so they may not offer sufficient protection. I suggest avoiding using Schottky diodes for reverse protection.

PNP Transistor A greatly improved protection circuit can be provided by using a pnp transistor as a high-side switch as shown in the second circuit.

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The saturated voltage is much lower than it is with diodes, so the voltage drop and power loss are much lower. The limitations of this approach is the fact that there is some power loss from the base current, and that loss is constant regardless of the circuit's current power draw. In circuits where a very low quiescent current is typical, this approach could greatly increase it. For circuits which are usually active and draw modest amounts of power, this simple type of protection is hard to beat.

Please note that the FET is actually installed in the reverse orientation as it would normally be used. This direction is so that the slight leakage current through the FET's intrinsic body diode will bias the FET on when the polarity is correct and block current when reversed, thus shutting off the FET.

If the supply voltage is less than the FETs maximum gate to source voltage, you only need the FET, without the diode or resistor. Just connect the gate directly to ground. If after checking your FET's spec sheet, you find that Vcc could exceed the maximum Vgs, then you must drop the voltage between the gate and the source.Ever blow up a circuit because you reversed the polarity of a battery? Or got one of those pesky center-negative AC power bricks?

Or even carefully connected your circuit to a bench supply, and still got the leads reversed? Well, I have. It can ruin your day. The easiest way to protect your system from a reversed battery is seen in the first image.

If you don't care about your system's efficiency, and you have at least 0. RLOAD represents whatever the heck you're running -- a microcontroller, a coffee warmer, whatever. However, if you have less than 0. This brings your drop down to 0. Better, but still not great. So, what's a guy or gal to do? The third image shows a simple trick for reverse polarity protection that has a minimal voltage drop across the protection device. In this case, the FET behaves like a low-value resistor.

Simple as that. And it can handle up to 60 Amps, so it's effective for low and high current applications. As your operating voltage goes up, a whole plethora of transistors open up, that may be better suited for your application, and cheaper. Just be sure to look at the RDSon vs. Vgs chart on your proposed transistor. Once you learn to peruse the DigiKey search engine and scan the data sheets, you can find transistors pretty quickly.In the simplest electrical circuits, there are three factors: current, or the flow of electricity; pressure, or the force required to cause the current to flow; and resistance, or the force required to regulate the flow of current.

Resistance is the restriction to current flow in an electrical circuit. Every component in the circuit, including the conductor, has some resistance to current flow. Current flows easier through some conductors than others; that is, the resistance of some conductors is less than others. Resistance depends on the material, the cross-sectional area, and the temperature of the conductor. The unit of electrical resistance is the ohm. It is designated by the letter R.

A simple electrical circuit is shown by figure This circuit includes two meters for electrical measurement: a voltmeter, and an ammeter. It also shows a symbol for a battery. The longer line of the symbol represents the positive terminal. The arrow shows the direction of current flow.

The ammeter is a low resistance meter shown by the round circle and arrow adjacent to the letter I. The pressure or voltage across the battery can be measured by a voltmeter. The voltmeter is a high resistance meter shown by the round circle and arrow adjacent to the letter E. The resistance in the circuit is shown by a zigzag symbol. The resistance of a resistor can be measured by an ohmmeter. An ohmmeter must never be used to measure resistance in a circuit when current is flowing.

Arc Welding Circuit.

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A few changes to the circuit shown by figureabove, can be made to represent an arc welding circuit. Replace the battery with a welding generator, since they are both a source of EMF or voltageand replace the resistor with a welding arc which is also a resistance to current flow. The arc welding circuit is shown by figure The current will flow from the negative terminal through the resistance of the arc to the positive terminal.

In the early days of arc weldingwhen welding was done with bare metal electrodes on steel, it was normal to connect the positive side of the generator to the work and the negative side to the electrode. This provided 65 to 75 percent of the heat to the work side of the circuit to increase penetration. When welding with the electrode negative, the polarity of the welding current was termed straight. When conditions such as welding cast iron or nonferrous metals made it advisable to minimize the heat in the base metal, the work was made negative and the electrode positive, and the welding current polarity was said to be reverse.

In order to change the polarity of the welding current, it was necessary to remove the cables from the machine terminals and replace them in the reverse position.Latest Projects Education.

General Electronics Chat DC polarity reverse. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. DC polarity reverse. Thread starter xxxyyyba Start date Jan 18, Search Forums New Posts.

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Thread Starter xxxyyyba Joined Aug 7, Here is simple circuit for DC polarity reverse. When one press switch 1 switch 2 is offS1 will close, S2 will open and S3 will close.

Scroll to continue with content. Just use a double pole double throw switch. Reloadron Joined Jan 15, 5, My question is, how would one realize switch 1 in practice? Thanks for replies. I want to control DC motor for moving satellite dish. It is absolutely necessary you will see why that these switches have some kind of spring inside them so when one press them they will close but as soon as one move hand away of them they come in "original" state.

If you know what I mean Here is schematic: Under normal circumstances satellite dish didn't reach maximal left or right position S1 and S4 will be closed and direction of moving satellite dish will be controlled using S2 and S3.

reverse polarity dc circuit

S1 and S4 will be mounted next to satellite dish so when satellite dish reaches for example maximal left position there will be physical contact between it and S1 and S1 will open. When satellite dish reaches maximal right position there will be physical contact between it and S4 and S4 will open. Now if satellite dish reach maximal left position, S1 will open and let's say that for moving satellite dish to left one has to press S2 : Now satellite dish can't go left anymore but we can move it in opposite direction if we press S3: Because of it's internal construction, S1 will close as soon as physical contact between it and satellite dish disappear: Similarly, if satellite dish reach maximal right position, S4 will open and let's say that for moving satellite dish to left one has to press S3 : Now satellite dish can't go right anymore but we can move it in opposite direction if we press S2: Because of it's internal construction, S4 will close as soon as physical contact between it and satellite dish disappear: What do you think?

Where can I find these switches? Last edited: Jan 19, OK, this would have gone better if you explained the project in the first post. You are talking about employing "Limit Switches" so when the motor reaches full travel in either direction the motor will stop.

The below circuits are similar to what you have. There are two examples of using limit switches. SW 2 and SW 3 are limit switches.

I would use what I call Micro Switches. The link explains them and shows the different styles, you will see how they can serve as limit switches. Something you need to consider is these drawings are rough drawings.

reverse polarity dc circuit

The switches are not specified as to their ratings. I have no idea what the current draw is of your motor. You need to make sure any components used can handle your DC currents for the motor! If the motor is high current then these switches would be used to turn on and off large relays or contactors to handle your motor current.

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What do you think?Connecting power with incorrect polarity is an easy mistake to make. Fortunately, protecting your device from reverse polarity is also quite easy. Reverse polarity can also occur after the testing and development phase.

reverse polarity dc circuit

A device will generally be designed so as to prevent the end user from incorrectly plugging in a power cable, but even the best of us might occasionally insert a battery without looking at the polarity diagram I prefer to use whatever means are available to make reverse polarity physically impossible, but the bottom line is that the device is never truly safe unless the circuit itself is able to survive a reversed supply voltage.

You can, in fact, get reverse polarity protection with a diode.

What is the best Reverse Voltage Protection Circuit? -- Repairing a Lab Bench Power Supply

Yes, all you need is one diode. This really does work, but of course a more sophisticated solution could provide superior performance. Thus, in a reverse-polarity situation, damaging reverse currents cannot flow and the voltage across the load is not the same as the reversed power-supply voltage because the diode functions like an open circuit.

The LTspice schematic shown above allows us to investigate the transient and steady-state behavior of the diode-based protection circuit. The power-supply voltage is initially at 0 V, then it abruptly changes to โ€”3 V.

My idea here is to simulate the effect of incorrectly inserting two 1. The simulation includes load resistance corresponding to a circuit that consumes about 3 mA and load capacitance corresponding to decoupling caps for a few ICs. You can see that some reverse i.

Reverse Polarity Protection: How to Protect Your Circuits Using Only a Diode

The transient current is very small and the longer-term current is miniscule. However, current is flowing and consequently the cathode side is not completely floating; instead, there is a very small reverse voltage across the load circuitry.

This is not the steady-state condition, though. If we extend the simulation out to ms, we see the following:. So as the load capacitance charges up and becomes an open circuit, the current falls to zero or more precisely, 0. There are definitely disadvantages that need to be considered, though:. An easy way to mitigate both of the above disadvantages is to use a Schottky diode instead of a normal diode.

This approach reduces voltage loss and power dissipation. Here is a plot of the transient and steady-state response of the Schottky-based reverse-polarity-protection circuit. You can see that the reverse current and the reverse voltage across the load are much larger than what we observed with the non-Schottky diode.

This higher reverse leakage current is a known disadvantage of Schottky diodes, though in this particular application the reverse current is still far lower than anything that would cause serious concern. So when it comes to reverse-polarity protection, Schottky diodes are definitely preferred. Schottky diodes have lower forward voltage and consequently are generally a better choice than normal diodes. Someone can also use a PMOS in reverse its drain, not its source pin, toward the source of alimentationload on the low side and then, just a low 0.

It also explain WHY it works not necessary evident at first glance that just a small 0.


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