» Electronics "Do-it-yourself polarity reversal protection board

DIY polarity reversal protection board


Greetings the inhabitants of our site!
As you know, many home-made, as well as factory devices often do not have protection against improper inclusion of the power polarity, in other words they do not have protection against power supply reversal. In particular, this applies to various homemade products, as well as to finished devices, sound amplifiers, mortise sound modules, etc.

Any user, by negligence, may accidentally invert the polarity of the power supply, after which, in the vast majority of cases, the device may require urgent help in the form of repair. And it may even happen that the device after such bullying will simply become worthless, and any repair will not help to bring it back to life.

In order to avoid such an unpleasant situation, protection from reverse polarity should be used. They are different. One of the most popular options is the use of powering diodes or diode bridges, which are capable of transmitting current in only one direction and thereby preventing the possibility of polarity reversal. This is a fairly budgetary and most simple solution. But there is a minus to this method of protection, namely, the presence of a voltage drop across the diode. Do not forget also that at high currents and the presence of a voltage drop, the diodes heat up rather weakly and if cooling is not used, they can fail.

For example, a diode bridge is installed on this sound amplifier with a TDA7377 chip.

In this case, it is primarily used here as a voltage rectifier when powered by an alternating voltage current source. But if you connect the device to a power source with a constant voltage, then this diode bridge works precisely as protection against reverse polarity. And no matter how we connect the battery, the diode bridge will prevent reverse polarity by passing current in the right direction.

And if instead of the diode bridge there was just a diode in the plus, then if the power is connected incorrectly (polarity reversal), the diode will not pass current and the amplifier simply will not turn on.

But, as mentioned above, both the diode bridge and the diode have a voltage drop. To demonstrate this, the author of the Radio-Lab YouTube channel measured the voltage before and immediately after the diode bridge.


As you can see, the voltage on the battery is 12.06V, and already after the diode bridge the voltage is about 1.5V lower. It seems that the losses are not so big, but this in turn will affect the power of the amplifier, as a result, it will be slightly lower and part of the battery energy will be used to heat the diode bridge.

Let's calculate the loss and heat generation on a diode bridge. For example, when the load current is 2A and the voltage drop across the diode bridge is 1.5V, the heat generation on the diode bridge will be about 3W. And additional losses are not a plus, especially when powering the sound amplifier or other device from the battery, where it is advisable to spend energy sparingly and its amount in the battery is limited.

Here is a comparison of the voltage drop across a conventional diode:


As you can see, it is about 0.4V. On the Schottky diode, the voltage drop is already lower and amounts to 0.2V.

The voltage drop across the diode bridge is the largest and is 0.6V.

During loading, voltage drops may be slightly higher. In fact, it is not often possible to confuse the polarity of the supply, but the loss in the presence of a drop on the diodes or diode bridge will be constant and as a result there will be heating, which in turn leads to the need for cooling. As you can see, diodes can be used as protection against reverse polarity, they work, but you still want better protection so that there is no heating, losses are minimal, and good operating currents.
The author offers one simple, but rather good protection scheme against reverse polarity power supply on a powerful field-effect transistor.

This circuit is suitable for protecting devices with unipolar power. Power Field Effect Transistor - IRF1405 is a powerful N-channel.


Such a transistor is capable of switching a sufficiently large current and, in turn, has a fairly small resistance, due to which there will be practically no voltage drop, and, therefore, there will be almost no heating, or it will be minimal, there will be no such losses as on diodes.

The author drew such a miniature scarf for this protection scheme.

The operation of the circuit is extremely simple: if everything is correctly connected, the transistor is open, and the current passes through the transistor.

If the polarity of the power supply is not connected correctly, the transistor closes, thereby creating a gap in the power circuit and the entangled plus fails to pass further.

On the radio market, all the necessary parts for the assembly of the protection board were purchased.

First of all, the author installs a 100kΩ resistor in place and solders it.

Next, we will install the zener diodes on 15V 0.5W, be sure to observe the polarity on the cathode marks.

Next, install a non-polar capacitor with a capacity of 0.1 μF.

Now terminal blocks for input and output power.

The board is almost ready, there is only one element left - a power transistor. To install it, the author bent the legs of the transistor - like this:


And set it in its place. The result is such a small and convenient power protection reverse polarity protection board for amplifiers and devices with unipolar power supply. Unipolar power is where there are two power wires: plus and minus.

After soldering, the circuit board must be washed with flux residues, so that everything is clean and beautiful.

Now let's check the functionality of the protection board we have assembled. To test the board, connect a battery with a power supply voltage of 12.1V to its input. The author connected the multimeter probes to the output of the board. First, we connect the battery correctly, observing the polarity.

As you can see, there is voltage at the output of the board, and the voltage drop is so low that the multimeter does not notice it.
Now we change the polarity of the power and connect the battery, confusing the plus with the minus.

As you can see, the transistor is closed, the protection board has worked and does not pass anything, thereby protecting the device (in this example, a multimeter) from reverse polarity. If you reconnect the power correctly, the transistor will open and the battery voltage will appear at the output of the board. Great, the board is working.
After we tested the homemade board and made sure that it works, you can connect the protection board to the sound amplifier. We will use the simplest amplifier on the TDA7377 chip without any protection against reverse polarity, and if the power polarity is confused, then at least the polar capacitor in power will explode and the chip will burn.

The protection board is connected to the gap of the plus and minus power supply of the amplifier, on which there is a possibility of polarity reversal. We must connect the power wires coming from the protection board to the amplifier board observing the polarity.

That's it, now our amplifier has protection, and the polarity reversal is not afraid of him. We connect the power correctly.

As you can see, the LED on the amplifier lights up, everything is fine, the amplifier has power. And now, we connect the power by reversing the polarity.

As you can see, nothing is smoking and the LED on the amplifier board does not light, therefore, the amplifier does not receive power, which means that our home-made protection board is working and fully fulfills its task.

This board can be used to protect against reversal of sound amplifiers with unipolar power, including class D amplifiers too, portable speakers and many other devices. Remember, if there is at least the slightest chance of reversing the polarity of the power supply, then at the right time, at least, protection from reverse polarity will save you money and protect your product from accidental reverse polarity and as a result of breakage.

It is also important to understand that in some cases it is more convenient to use diodes or a diode bridge as protection against reverse polarity, and in others it is necessary to look at the assembled protection board for tasks. Try, collect and repeat. Archive with the board can be downloaded HERE.
Thank you for attention. See you soon!

Video:
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82 commentary
What does the relay response time have to do with it? Look carefully at the diagram.
Explain your deep thought.
Adartasov Alexander Viktorovich
Respect for those who are for a simple diode bridge, cost-effective, reliable and not confused.
Adartasov Alexander Viktorovich
the contact flight time is slower than the burn-in time of the microcircuit.
Adartasov Alexander Viktorovich
as an old telegraph operator, I can say that all important military radiograms are especially ALWAYS !!! in those years they were taken for recording only with simple pencils (there were dozens of prepared quivers on the table), and children's doubts about not writing pencils in the sandbox rub young animals. Sorry for the homespun truth that you don’t know about, felt-tip youth ...
I read the most commented note and comments. I soldered the circuit on the NDP603 ... (30 V, 25 (100) A, 50 W, 0.022 Ohms). Until a resistor of several kOhm was sealed in parallel to the zener diodes, the circuit let current in both directions,did not work. After sealing the resistor, it worked fine, and with a current of up to about 4 A without a radiator on the field.
And think about it? The protective diode is the cathode to the drain. In the forward direction, it will be turned on with the correct polarity.
Guest Alexander Volkov
The scheme is not working !!! The parasitic diode in the transistor will pass the current in the opposite direction. Author, do you even think about circuitry?
In the old fashioned way, just calling and waiting
- Hello, I've been waiting for your orange taxi for an hour! - You have been waiting for an hour Opel blue! xaxa
Perhaps truckers ... Or somewhere ... regionally, let’s say so ... In our city, as I already wrote, taxi drivers definitely don’t have walkie-talkies. And not only Yandex ... (At us (Brest) they also appeared). A bunch of companies now and yet puffing in front of each other, competing))). And it’s good for the people - and taxis have become available even to students, and the cars are newer and more pleasant ... And the Wi-Fi is free for everyone in the car while you are driving ... And everyone is now calling from a smartphone, so that later they can watch through jeepies where the car is , will soon arrive ... (They are all with the "beacons"). It’s more convenient ... If you send one child, you can also follow, for example ...
P.S. Himself I go by taxi very, very rarely ... Not every year ... Once - constantly driving))))
I do not track from a smartphone ... In the old fashioned way, I just call and wait.))))
P.P.S. Only recently we have become a lot of female drivers ?. Or everywhere?
ozi
Up to 2 And I would limit myself to one sequential Schottky diode with a plus power. And the diode is not so heated, and the voltage loss is not large. The bridge will eat twice as much, often this is critical. There is another problem - working with a device that is associated with other devices. Zero-ground must be hard. The diode bridge does not provide this. And in this scheme, the minus (often the case) would be better if it were direct, but the plus would turn off.
Guest Alexander
Oh, how absurd

To read comments is a zapadlo. Right? But flashing your mind - this is the topic !!!
Guest Alexander
Oh, how absurd, how difficult ....
A dull diode bridge - and you can turn it on even in reverse polarity: the circuit will correct. True, it will take Volta's shares as a voltage drop across the diodes. This, of course, must be taken into account. Accordingly, the diodes are selected according to the forward current and reverse voltage, taking into account the jump during the transient process when turned on.
Guest Sergey
Valery, now there is a CBS car antenna shortened mini, so 20 centimeters long. They are almost not noticeable. You probably saw 2.5-meter quarter-wave long whips, but you can be surprised at them, and now almost, but not all, go with shortened C-B antennas 60 -70 centimeters long. You can look at the sizes of antennas on the Internet.
Guest Sergey
Addition . Previously, permission was required to work in the CBC range. Now permission is not required. Buy CBS r \ s and use.
Guest Sergey
Addition . Previously, permission to work in the CBC range was required; a small amount had to be paid. Some time ago (probably 5 years or more), the rules of work on this range were changed. Now no permissions are required. You buy r \ with C-Bi, an antenna and use it for your health. Many northerners and not only buy these radio stations for travel by car on vacation, in order to know the traffic situation.
Guest Sergey
. Also in small cities taxi use the same radio stations. There are also VHF car radio stations, they are also used by taxi drivers.

Now? That is, taxi drivers widely used walkie-talkies. But now it’s already about five years, as everyone is sitting on the Internet. At the very least, a car with an antenna is now catching on ... We only have a Walkie Talkie Club. So walkie-talkies - only they left. They talk there, gather for meetings, pay dues, as usual, transferring part in favor of orphans ... (The management of all clubs, collecting money, strive to present this in a noble way)))) ... Well, in short , an ordinary interest club ..
Yes, I didn’t think about automobiles. ((
Guest Sergey
Ivan, there are CBS car radio stations, they do not have chargers. Truckers and other drivers on channel 15 of AM use these r / s. Also in small towns taxi use the same radio stations. There are also VHF car radio stations, taxi drivers also use them.
Quote: Guest Sergey
Radios are regularly brought to me for repairs ... with polarization and safety guards-bugs.
Explain how this could be. All radio stations, even the last household ones, not to mention Motorola, Kenwood and the like, are equipped with full-time memory devices, which, on the contrary, simply cannot be pushed into which the radio.
What did the wretched want to say?
Bad parenting does not make know-it-all and the ultimate truth!
And such 95 % . I regularly carry radios for repairs ...with polarization
Is the figure from the ceiling taken?
Korolev understood very well who they called Nerod ...
But wretched it is necessary to chew ....))))
P.S. It seems that he has already voiced the trend: the dumber a person - the more aggressive he blames others for this ... smiles
Guest Sergey
What did the wretched want to say? NOROD - are illiterate individuals who have no idea about electricity, and not just about electronics. And such 95%. Radios are regularly brought to me for repairs ... with polarization and safety guards-bugs.
Guest Alex
How many inclusions can the diode withstand? Self induction?
Guest Alex
the diode is also a replacement - it will be damaged
Our Nrod will not bother
Your NOROD will not bother you with electronic homemade goods! ok
Guest Sergey
The little "specialists" are advised to put a diode and a fuse. "Specialists" probably do not know that a bug will be put in place of a burnt out fuse and the electronic device will certainly burn. Our Nrod will not bother and find out what the fuse, the paper clip, the coin and the nail from is blown for, rather it will put in place of the fuse.
Guest Vladimir
And if the output voltage is adjustable? Then what about the relay?
If a replacement is made, then the price of this design is rubles. Polevik can be applied from the motherboard, the motherboard to 100r on the flea markets.
MOS transistors are fairly symmetrical semiconductor products; according to old Western standards, there was no difference between their drain and source in their UGO.
In this scheme, when the source is connected correctly, the source produces a small plus relative to the drain (at the first moment it is about 0.5 ... 0.7 V, and after the transistor is opened with a plus at the gate, the difference will be about tens of millivolts). With such a low voltage, there is no significant difference between the drain and the source. By and large, the main difference between the drain and the source is where the spurious (aka protective) diode is connected.
Why is the (- minus) fed to the drain of the n-channel field effect transistor in this circuit?
Especially for the smartest and most stubborn, I’ll explain: DC IN - not just some Latin letters, but Direct Current Input - entrance by direct current. And it is to these contacts that an external power source is connected. Point marked as ground is inside scheme to her source not connected. Moreover, it is completely incomprehensible why the author of the scheme so designated it. ((
For starters, you yourself would have looked at the circuit before fantasizing: with a polarity reversal, plus will be at the cathode protective diode.
And this is the "Chukchi of the second type": about the protective diode.
Guest Fedor
Quote: Ivan_Pokhmelev
The protective diode is the cathode to the drain. In the forward direction, it will be turned on with the correct polarity.

Look at the diagram - the anode of the protective diode of the transistor is stuck in the ground. It is necessary to do a reverse polarity and get a plus on the ground, which calmly through the diode will be in the circuit. The second wire goes straight ahead.
Yes, the Chukchi continue to jamb. )))
Putandon, however! smile
And if you put a diode bridge on their way?
I can’t even imagine its power! xaxa
Yes, the Chukchi continue to jamb. )))

And if you put a diode bridge on their way? boss xaxa
Yes, the Chukchi continue to jamb. )))
What kind? Type can you name?
Ivan PohmelevYou are frankly trolling laugh1
Gregory
And if you put a diode bridge at the entrance, then in general the problem of polarity disappears.
Guest Vita
Today I want to be a writer. Recently, he commented on two authors: one answered my "smart" questions professionally, the other immediately began to write epigrams "about spitting in the wind." I want to wish you patience, at least that moment, while your homemade product comes to everyone's hand. And "in the bust" do not remember anyone ..
Guest Vita
Now there are self-healing (high-speed).
Guest Vita
It is possible in parallel, if there is no suitable current. Yes, and here we must think what needs to be considered.
Something you mess today. )))
Spring, however, is frozen, however! dance2
You forgot about the speed of these fuses, so they will probably turn off the already broken circuit.
Without reading the comments, we begin to write your own? Another Chukchi is not a reader, Chukchi is a writer? Something you mess today. )))
And you can do without diodes and put only one self-stopping fuse, but this is the last resort if it is more or less known how the circuit behaves and the breakdown current is determined experimentally. Although why do you need protection against polarity reversal? If a person doesn’t often “accept” then it’s not necessary
Guest Vladimir
Put a diode bridge and the same thing will be

We advise you to read:

Hand it for the smartphone ...