A protection design for any type of power supply is presented. This protection circuit can work together with any power supply - mains, switching and DC batteries. The schematic decoupling of such a protection unit is relatively simple and consists of several components.
Power supply protection circuit
The power part - a powerful field-effect transistor - does not overheat during operation, therefore it does not need a heat sink either. The circuit is at the same time a protection against power overload, overload and short circuit at the output, the protection operation current can be selected by selecting the resistance of the shunt resistor, in my case the current is 8 Amperes, 6 resistors of 5 watts 0.1 Ohm connected in parallel were used. The shunt can also be made from resistors with a power of 1-3 watts.
The protection can be more accurately adjusted by selecting the resistance of the trimming resistor. Power supply protection circuit, current limit regulator Power supply protection circuit, current limit regulator
~~~In the event of a short circuit and overload of the unit output, the protection will instantly operate, turning off the power source. An LED indicator will indicate that the protection has been triggered. Even if the output short-circuits for a couple of tens of seconds, the field-effect transistor remains cold
~~~The field-effect transistor is not critical; any switches with a current of 15-20 Amps or higher and an operating voltage of 20-60 Volts will do. Keys from the IRFZ24, IRFZ40, IRFZ44, IRFZ46, IRFZ48 line or more powerful ones - IRF3205, IRL3705, IRL2505 and the like are ideal.
~~~This circuit is also great for protecting a charger for car batteries; if the connection polarity is suddenly reversed, then nothing bad will happen to the charger; the protection will save the device in such situations.
~~~Thanks to the fast operation of the protection, it can be successfully used for pulsed circuits; in the event of a short circuit, the protection will operate faster than the power switches of the switching power supply have time to burn out. The circuit is also suitable for pulse inverters, as current protection. If there is an overload or short circuit in the secondary circuit of the inverter, the inverter's power transistors instantly fly out, and such protection will prevent this from happening.
Comments
Short circuit protection, polarity reversal and overload are assembled on a separate board. The power transistor was used in the IRFZ44 series, but if desired, it can be replaced with a more powerful IRF3205 or with any other power switch that has similar parameters. You can use keys from the IRFZ24, IRFZ40, IRFZ46, IRFZ48 line and other keys with a current of more than 20 Amps. During operation, the field-effect transistor remains icy. therefore it does not need a heat sink.
The second transistor is also not critical; in my case, a high-voltage bipolar transistor of the MJE13003 series was used, but there is a large choice. The protection current is selected based on the shunt resistance - in my case, 6 0.1 Ohm resistors in parallel, the protection is triggered at a load of 6-7 Amps. You can set it more precisely by rotating the variable resistor, so I set the operating current to around 5 Amps.
The power of the power supply is quite decent, the output current reaches 6-7 Amps, which is quite enough to charge a car battery.
I chose shunt resistors with a power of 5 watts, but 2-3 watts is also possible.
If everything is done correctly, the unit starts working immediately, close the output, the protection LED should light up, which will light up as long as the output wires are in short-circuit mode.
If everything works as it should, then we proceed further. Assembling the indicator circuit.
The circuit is copied from a battery screwdriver charger. The red indicator indicates that there is output voltage at the power supply output, the green indicator shows the charging process. With this arrangement of components, the green indicator will gradually go out and finally go out when the voltage on the battery is 12.2-12.4 Volts; when the battery is disconnected, the indicator will not light up. 
Charger for car batteries
Offered to the attention of readers Charger does not have any specific features and is built according to a long-proven scheme. Due to the fact that most car enthusiasts like to “spark” the charger, and this leads to failure of some of its elements, it was proposed to install short circuit protection.
Operating principle of the charger
When the device is turned on with the toggle switch SA1, the phase-pulse generator VT1, VT2 is supplied with a voltage limited by the zener diode VD5. From the generator output, control pulses are sent to the control electrode of thyristor VS2. Variable resistor R6 is used to smoothly set the charging current level. If a short circuit occurs or the battery poles are incorrectly connected, the voltage across resistor R12 increases. Then the zener diode VD8 and thyristor VS1 open. The thyristor bypasses capacitor C1, which determines the pulse frequency of the generator. The supply of control pulses to thyristor VS2 stops. The charging current stops. To control the charging current, microammeter P1 is used in voltmeter mode. It measures the voltage drop across resistor R12, which serves as a current sensor for the short circuit protection circuit. The voltage drop across this resistor is directly proportional to the current flowing through it. The microammeter in this current measurement circuit is reliably protected by resistor R13 and will not fail even if it goes off scale.
The control circuit with protection is mounted on the board using any type of mounting (who prefers what). With proper installation and serviceable parts, the device is operational immediately after switching on.
Schematic diagram of the charger
Design
Charger assembled in any convenient size housing. The case must have enough ventilation holes to cool the device during long periods of operation. The front panel contains device P1, resistor R6, toggle switch SA1, fuses FU1 and FU2, and warning lamp HL1. Output sockets-clamps (terminals) are installed at the request of the designer. Alligator clips of appropriate sizes are soldered onto the ends of the wires for connection to the battery poles. The clamps must be of different colors to avoid possible connection errors. A corresponding inscription is applied to the front panel near each element.
The parts used are not particularly scarce. A TS-180 from an old black and white TV is used as a power transformer. The transformer is carefully disassembled and all secondary windings are wound up. Then they wind each half with a wire with a diameter of 1.4...1.5 mm in any insulation, 34 turns. The transformer is being assembled. The windings are connected in series and checked with an AC voltmeter. The voltage should be within 20...22 V.
Details
Capacitors: C1 - MBM, K73P-3, K73-17; C2, SZ - K50-12, K50-35, etc.
Resistors (except R12) type MLT-0.25. R1 - MLT-2.0, R2 - MLT-1.0, R6 - SP1, SP2, SP2-1, etc. Resistor R12 is a piece of nichrome wire with a diameter of 0.8...1.5 mm.
Signal lamp HL1 -МН6,ЗхО,26. Device P1 is a microammeter for a current of no more than 300 mA.
Bridge diodes VD1 ... VD4 - D242, D243, KD213 and other diodes are mounted on radiators made of aluminum or duralumin alloy. The area of one side is at least 49 cm2 (size 7x7 cm) for one diode at a current of 10 A. Diodes VD6, VD7 - D220, D223 and other silicon with 11 arr. at least 50 V. Zener diodes VD5 - types D814B, V, G, D ( not critical), VD8 - KS133, 139, 147, 151,156 (not critical). Thyristor VS1 - type KU201 with any letter. Thyristor VS2 type KU202 from the letter B onwards, T25, etc. The thyristor is installed on a radiator with an area of one side of 100 cm2 (size 10x10 cm). Transistors VT1 - KT361, KT209, etc., VT2 - KT315, KT201, etc.
Resistor R13 in microammeter circuits is selected depending on the type of head used. Instead, a variable resistor with a resistance of 33 kOhm is temporarily soldered in and the instrument pointer is set to the end mark of the scale at a current of 10 A. Then the resistance is measured (having previously soldered one wire) and a constant resistor is soldered in instead. If a magnetoelectric system device is used, the scale will be linear.
V. I. Zhuravlev, Efremov
I have a simple charger at home. Ordinary charging, transformer, bridge and wires. The protective films on the terminals have peeled off, and now how can you tell who is where! It was decided to assemble a simple protection device. I’ll say that I’ve seen something similar before, but I had to make it up myself. There was just a relay with UPS with 10A contacts.
The scheme works on this principle. When you connect the terminals to the battery correctly, the remaining charge in the battery closes the relay and charging begins, the green LED lights up. When you have mixed up the terminals, the red LED lights up, signaling that you have connected incorrectly. A simple device with just a few parts
Here is the reverse polarity protection circuit
R1-2 = 510
VD1-2= 1N4148 (But any are possible) VD3-4 can be excluded
Relyukha 12V 10-15A, as I said earlier, I took it from a broken UPS
Any LEDs
Reverse polarity protection device printed circuit board:
For safe, high-quality and reliable charging of any types of batteries, I recommend
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Don’t want to delve into the routine of radio electronics? I recommend paying attention to the proposals of our Chinese friends. For a very reasonable price you can purchase quite high-quality chargers
A simple charger with an LED charging indicator, green battery is charging, red battery is charged.
There is short circuit protection and reverse polarity protection. Perfect for charging Moto batteries with a capacity of up to 20A/h; a 9A/h battery will charge in 7 hours, 20A/h in 16 hours. The price for this charger is only 403 rubles, free delivery
This type of charger is capable of automatically charging almost any type of 12V car and motorcycle batteries up to 80A/H. It has a unique charging method in three stages: 1. Constant current charging, 2. Constant voltage charging, 3. Drop charging up to 100%.
There are two indicators on the front panel, the first indicates the voltage and charging percentage, the second indicates the charging current.
Quite a high-quality device for home needs, the price is just RUR 781.96, free delivery. At the time of writing these lines number of orders 1392, grade 4.8 out of 5. Eurofork
Charger for a wide variety of 12-24V battery types with current up to 10A and peak current 12A. Able to charge Helium batteries and SA\SA. The charging technology is the same as the previous one in three stages. The charger is capable of charging both automatically and manually. The panel has an LCD indicator indicating voltage, charging current and charging percentage.
A good device if you need to charge all possible types of batteries of any capacity, up to 150Ah
The price for this miracle 1,625 rubles, delivery is free. At the time of writing these lines, the number 23 orders, grade 4.7 out of 5. When ordering, do not forget to indicate Eurofork
If any product has become unavailable, please write in the comment at the bottom of the page.
I have a simple charger at home. Ordinary charging, transformer, bridge and wires. The protective films on the terminals have peeled off, and now how can you tell who is where! It was decided to assemble a simple protection device. I’ll say that I’ve seen something similar before, but I had to make it up myself. There was just a relay with UPS with 10A contacts.
The scheme works on this principle. When you connect the terminals to the battery correctly, the remaining charge in the battery closes the relay and charging begins, the green LED lights up. When you have mixed up the terminals, the red LED lights up, signaling that you have connected incorrectly. A simple device with just a few parts
Here is the reverse polarity protection circuit
R1-2 = 510
VD1-2= 1N4148 (But any are possible) VD3-4 can be excluded
Relyukha 12V 10-15A, as I said earlier, I took it from a broken UPS
Any LEDs
Reverse polarity protection device printed circuit board:
We connect like this:
Z+ - plus of the charger, there are two of them, determine which one you need yourself, since some relays of this type close the contacts in different ways
A+ - battery plus. Connect the battery positive terminal here
G is a minus, throw it with a thin wire from the minus of charging
The circuit was soldered in 5 minutes, and showed itself to be quite worthy in operation. Good luck with your repetition
Update. To replace this scheme, I came up with an even better protection scheme, which, in addition to all the functions inherent in the old scheme, can also determine how long the battery is alive. Which will save you from problems such as burnout of the charger due to old dead batteries. You can see my new development
For safe, high-quality and reliable charging of any types of batteries, I recommend
With uv. Admin check
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Let's make a gift to the workshop. Throw a couple of coins at the UNI-T UTD2025CL digital oscilloscope (2 channels x 25 MHz). An oscilloscope is a device designed to study the amplitude and time parameters of an electrical signal. It costs 15,490 rubles, I can’t afford such a gift. The device is very necessary. With it, the number of new interesting schemes will increase significantly. Thanks to everyone who will help.
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n-channel MOSFET + 7.2...15V zener diode + resistor of a couple of tens of kilo-ohms = SAFETY
The task seems to be trivial. And why would anyone ever need to protect any electronic products from power supply reverse polarity?
Alas, an insidious case has a thousand and one ways to slip a minus instead of a plus onto a device that you spent many days assembling and debugging, and now it just started working.
I will give just a few examples of potential killers of electronic breadboards, and finished products too:
- Universal power supplies with their universal plugs, which can be connected either with a plus on the internal contact or with a minus.
- Small power supplies (such boxes on the power plug) - they are all produced with a plus on the central contact, aren’t they? NO!
- Any type of connector for power supply without a hard mechanical “key”. For example, convenient and cheap computer “jumpers” with a pitch of 2.54mm. Or screw clamps.
- How do you like this scenario: the day before yesterday there were only black and blue wires at hand. Today I was sure that the "minus" is the blue wire. Chpok - that's a mistake. At first I wanted to use black and red.
- Yes, just if you have a bad day - mix up a couple of wires, or plug them in the other way around simply because you were holding the board upside down...
There will always be people (I know at least two such peppers) who, looking straight into the eyes, will firmly and categorically declare that they will never do such a stupid thing as reversing the polarity of the power source! God is their judge. Maybe after they themselves assemble and debug several original designs of their own design, they will become wiser. In the meantime, I won't argue. I'll just tell you what I use myself.
Life stories
I was still quite young when I had to resolder 25 out of 27 cases. Luckily, these were good old DIP microcircuits.
Since then, I almost always place a protective diode next to the power connector.
By the way, the topic of protection against incorrect power polarity is relevant not only at the prototyping stage.
Just recently I witnessed the heroic efforts of a friend to restore a giant laser cutter. The cause of the breakdown was a would-be technician who mixed up the power wires of the sensor/stabilizer for the vertical movement of the cutting head. Surprisingly, the circuit itself seems to have survived (it was, after all, protected by a diode in parallel). But everything burned out completely afterwards: amplifiers, some kind of logic, control of servos...
This is perhaps the simplest and safest option for protecting the load from power supply reverse polarity.
There is only one bad thing: the voltage drop across the diode. Depending on which diode is used, it can drop from about 0.2V (Schottky) and up to 0.7...1V - on conventional rectifier diodes with a p-n junction. Such losses may be unacceptable in the case of a battery-powered or stabilized power supply. Also, at relatively high current consumption, power losses on the diode can be very undesirable.
With this type of protection there are no losses during normal operation.
Unfortunately, in the event of a polarity reversal, the power supply runs the risk of breaking. And if the power source turns out to be too strong, the diode will burn out first, and then the entire circuit it protects.
In my practice, I sometimes used this type of reverse polarity protection, especially when I was sure that the power source had overcurrent protection. However, one day I earned very clear prints on my burnt fingers when I touched the radiator of the voltage stabilizer, which was trying to fight against a thick Schottky diode.
p-channel MOSFET - a successful but expensive solution
This relatively simple solution has virtually no drawbacks: a negligible voltage/power drop across the pass-through device in normal operation, and no current in the event of a polarity reversal.
The only problem: where to get high-quality, inexpensive, high-power p-channel field-effect transistors with an insulated gate? If you know, I will be grateful for the information 😉
All other things being equal, a p-channel MOSFET in any parameter will always be approximately three times worse than its n-channel counterparts. Usually, both the price and something to choose from are worse: open-channel resistance, maximum current, input capacitance, etc. This phenomenon is explained by approximately three times less mobility of holes than electrons.
n-channel MOSFET - the best protection
It’s not at all difficult to get a powerful low-voltage n-channel CMOS transistor these days; sometimes you can even get them for free (more on that later;). So providing a negligible open channel drop for any imaginable load current is a piece of cake.
N-channel MOSFET + 7.2...15V zener diode + resistor of a couple of tens of kilo-ohms = SAFETY
Just as in a circuit with a p-channel MOSFET, if the source is connected incorrectly, both the load and the unlucky source are out of danger.
The only “drawback” that a meticulous reader can notice in this protection scheme is that the protection is included in the so-called. "ground" wire.
This can indeed be inconvenient if a large earth star system is being built. But in this case, you just need to provide the same protection in the immediate vicinity of the power supply. If this option is not suitable, there will probably be ways to either provide such a complex system with unique power connectors with reliable mechanical keys, or install a “constant”, or at least “ground” without connectors.
Caution: static electricity!
We have all been warned many times that field-effect transistors are afraid of static discharges. This is true. Typically the gate can withstand 15...20 Volts. A little higher - and irreversible destruction of the insulator is inevitable. At the same time, there are cases when the field operator seems to still be working, but the parameters are worse, and the device can fail at any moment.
Fortunately (and unfortunately) powerful field-effect transistors have large capacitances between the gate and the rest of the crystal: from hundreds of picofarads to several nanofarads and more. Therefore, the discharge of the human body is often withstood without problems - the capacity is large enough so that the drained charge does not cause a dangerous increase in voltage. So when working with powerful field workers, it is often enough to observe minimal caution in terms of electrostatics and everything will be fine :)
I'm not alone
What I describe here is, without a doubt, a well-known practice. But if only those military industry developers had the habit of publishing their circuit designs on blogs...
Here's what I came across on the Internet:
> > I believe it is pretty well standard practice to use an N-channel
> > MOSFET in the return lead of military power supplies (28V input).
> > Drain to supply negative, source to the negative of the PSU and
> > the gate driven by a protected derivative of the positive supply.
Where to get MOSFETs for next to nothing
come see me a little later - there will be an article 😉
Application examples
Simple with power reverse polarity protection:
Happy experiments!
Were you interested? Write me!
Ask, suggest: in the comments, or in a personal message. Thank you!
All the best!
Sergei Patrushin.
Well, as promised - the second article, which is devoted to the polarity reversal protection system, which has found quite wide application in industrial and home-made chargers. This option was chosen as particularly simple and can be repeated even by a person who has nothing to do with electronics.
To implement such a protection circuit, you only need a diode - just one diode, which will be installed in the forward direction on the positive bus of the charger.
Such a system is just so simple that to modify the charger, it is not at all necessary to disassemble it. To implement this idea, we use the most important function of a semiconductor diode - in the forward direction the diode is open, but if it is connected in the reverse direction, it will be locked.
Consequently, if you suddenly confuse the polarity, then the current simply will not flow, no pops, heating or other smoke effects.
But as we know, when the voltage flows through the junction of the rectifier diode, then at the output of the latter there will be a voltage drop in the region of 0.7 Volts, precisely in order for the drop to be minimal, we will use SCHOTTTKY diodes (with a Schottky barrier) - there is a drop on it voltage is around 0.3-0.4 Volts.
The only drawback of such protection is that a fairly large current will flow through the diode, which leads to heating of the diode.
To do this, the diode must be installed on the heat sink. High current Schottky diodes can be found in computer power supplies. The diodes in the indicated blocks are a three-terminal diode assembly; each assembly contains two diodes with a common cathode. You need to select diodes with a current of at least 15 Amps per diode. In computer units there may be diodes with a current of up to 2x30 Amperes.
First you need to install a diode on the heat sink, then parallelize the anodes of the diodes, so we connected both diodes in parallel.
I wanted to put together something related to a battery charger. And the very first thing I thought of assembling was protection against polarity reversal on the relay.
But when searching the Internet for the required scheme, I did not find anything similar. And before that I saw it a year ago. I drew a diagram from memory and am ready to share it with you.
This device is needed to protect your battery and charging from damage, preventing you from mixing up the terminals and will save you from many problems.
Here is a diagram of a polarity reversal device for relay chargers.
Elements:
R1 = 510
Rel2 = 12V (Any 12V 10-15A, removed from a former UPS for a computer)
VD1-3= 1N4007 (I didn’t find any others).
Although VD3 is not required, you can use a jumper instead. VD1 from the self-induction of the relay coil.
This is how the device works. When you connect a battery, the remaining charge in it passes through the relay and closes the contacts, thereby supplying current from the charger to the battery.
If you connect the wires to the battery incorrectly, then VD2 will not allow electricity to pass through the relay and charging will not start. And instead of charging, the LED will light up, indicating that the charging is not connected correctly.
Here is a reverse polarity protection device for a PCB charger.
Reverse polarity protection device seal for the charger.
You can download the Sprint-Layout 5.0 seal for the reverse polarity protection device for the charger on the website in the source below.
I wanted to put together something related to a battery charger. And the very first thing I thought of assembling was protection against polarity reversal on the relay
But when searching the Internet for the required scheme, I did not find anything similar. And before that I saw it a year ago. I drew a diagram from memory and am ready to share with you
This device is needed to protect your battery and charging from damage, preventing you from mixing up the terminals, it will save you from many problems
Here is a diagram of a polarity reversal device for relay chargers
Elements:
R1 = 510
Rel2 = 12V (Any 12V 10-15A, removed from a former UPS for a computer)
VD1-3= 1N4007 (I didn’t find any others)
Although VD3 is not required, you can use a jumper instead. VD1 from the self-induction of the relay coil.
This is how the device works. When you connect a battery, the remaining charge in it passes through the relay and closes the contacts, thereby supplying current from the charger to the battery.
If you connect the wires to the battery incorrectly, then VD2 will not allow electricity to pass through the relay and charging will not start. And instead of charging, the LED will light up, indicating that the charging is not connected correctly
Here is a reverse polarity protection device for a charger on a printed circuit board
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