The positive temperature coefficient, PTC thermistor has two types: silistor & switching PTC have very different characteristics.

 

As the name indicates a positive temperature coefficient, PTC thermistor has a response in which the resistance rises with increasing temperature.

 

There are two types of PTC thermistor which have very different characteristics, one showing a linear increase, whilst the other shows a sudden change in resistance.

 

PTC thermistor outline

 

PTC thermistors can be divided into two types according to their structure and the materials used. The two types of PTC thermistor have very different characteristics:

 

  • Switching PTC thermistor:

This form of PTC thermistor is used in heaters, sensors and specialized versions are also used as resettable fuses. Switching type NTC thermistors have a highly non-linear curve. The resistance at first falls slightly with increasing temperature, and then at a critical temperature the resistance increases dramatically, thereby acting virtually as a switch. This makes it ideal in many protection devices.

  • Silistor:

The silistor PTC thermistor uses a semiconductor as its base material and it is characterized by a linear characteristic and as a result, the silistor is used in temperature sensors. The silistor PTC thermistor is generally manufactured from doped silicon, the level of doping determining the exact characteristics.

 

Switching PTC thermistor basics

 

As the switching PTC thermistor is very widely used form, it warrants further explanation as it has an unusual characteristic.

 

Switching PTC thermistors are typically fabricated from polycrystalline materials including barium carbonate or titanium oxide with added materials including tantalum, silica, or manganese, etc.

 

The materials are mixed and ground to fine powders and finally compressed into the required shapes before being sintered. Contacts are then added and the thermistor is encapsulated.

 

The characteristic of the switching PTC thermistor shows that the device has a highly non-linear characteristic. As the temperature increases, the resistance first decreases, then rising slightly before it reaches a critical temperature, TC. At the critical temperature the resistance increases sharply for any increase in temperature, before finally leveling off and falling slightly.

 

A similar type of device is known as a Polymer PTC. These devices consist of a plastic element into which carbon grains are embedded. When cool, the carbon is able to conduct electricity, but as the temperature increase the carbon grains move further away as a result of expansion and conduction falls rapidly. In this way the device acts like a switch in the same way as the more traditional PTC thermistors.

 

PTC thermistor operational modes

 

There are two main ways in which switching PTC thermistors are generally used.

 

  • Self-heating mode:

When used in the self-heating mode, current is passed through the thermistor, often in series with the item being controlled. As it heats up as a result of the current, it reaches a point where the critical temperature is reached and the resistance increases significantly. In this way it operates in a self-heating mode and can be used as a safety cut-out or regulator.

 

  • Sensor mode:

In this mode, a minimum amount of current is passed through the device and PTC thermistor senses the surrounding temperature. Keeping the current to a minimum ensures the self-heating effect is negligible and only the surrounding temperature affects the device. As the surroundings heat the device it may reach its critical temperature at which point the resistance will significantly increase.

 

Switching PTC thermistor applications

 

Switching thermistors are a very useful form of electronic component. It can perform functions with a single component that would require far more complex circuitry should any other technique be used.

 

  • In-rush protection:

Some electrical items like motors and transformers have a large surge of current at switch on. This gives rise to very high peaks of current which can cause spikes on the power line, or cause damage in some instances. PTC thermistors can be used to reduce the level of the inrush current and thereby prevent the spikes or damage occurring.

 

  • Overcurrent protection:

In this application, the PTC thermistor is placed in series with the load and uses the self-heating effect. The current taken under normal conditions should enable the thermistor to operate in its flat resistance curve area. However if an over-current condition arises, then the thermistor will carry more current and the temperature will rise more causing it to rise beyond the critical temperature when the resistance will rise significantly causing the current to drop.

 

PTC thermistor circuit symbol

 

It is sometimes necessary to indicate the type of thermistor being used on a circuit diagram. Accordingly the IEC have a special PTC thermistor circuit symbol that can be used.

 

As seen the circuit symbol utilizes the characters +t° to give an indication of the positive temperature coefficient.

 

Positive temperature coefficient, PTC thermistors are used in many electronic circuits and for a variety of functions. It is essential to check that the correct type is selected for any given circuit to ensure that its characteristic meets the requirements.

 

Zonkas is the experienced and reliable manufacturer of specializing in capacitor, inductor, and transformer. If you are still interested in PTC thermistors, welcome to visit the website of Zonkas.

 

 

Article Source: https://www.electronics-notes.com/articles/electronic_components/resistors/thermistor-ptc-positive-temperature-coefficient.php

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How to Choose an Electric Drop Bolt?

On August 28, 2017, in Electrode Products, by Lambert

Electric drop Bolt is called electric drop down bolt, drop bolts lock, electric bolt lock. It is usually installed to control the glass doors/gates. Electric drop bolt locks can be used with any kind of electronic digital on/off switches, magnetic stripe card reader, proximity card reader and biological access control system.

 

Drop bolt is made up of 2 parts-the face plate and body. Additionally there is a strike plate.

Electric Drop Bolt

 

The face plate is usually made of aluminum and body made of stainless steel.

 

Sensor Type – Generally there are 2 types sensor electric drop bolt in the market. Ball bearing sensor and magnetic sensor.

 

Working mode – There are 2 types working mode drop bolts, the failsafe and failsecure modes. Failsafe mode drop bolt is widely used nowadays due to when the power cut offer the drop bolt latch is unlocking. It ensures the people escape.

The failsecure drop bolt is used only in the high security place such as prisons which do not allow access if no valid command, regardless of any reasons.

 

Delay – Some drop bolts have delay function buy some not. The delay function is helpful to keep the door close properly every time when people push/pull the door and leave it closing by floor spring. The delay function provides the drop bolts ability that relock only when the door do not swing anymore. This is very useful to the door that floor spring works not well enough. It avoids the door impact the bolt latch by mistake. The user could adjust the delay time from 3/6/9 seconds as needs.

 

Cables – There are different quantity cables drop bolt in market. The different cable quantity drop bolts have different performance. 2-cable drop bolt is a basic level product which provides the basic function. When power on, the current drive the circle to generate electromagnetic effect, which attracts the spring sheet to keep locking. It is easy heat for a long term using. And the current fluctuate may easily causes malfunction to drop bolt.

 

Multi cables drop bolt provide more features such as door contact, REX, etc. A unique logic circuit keeps the drop-bolt retracted until the door has been closed and is properly aligned to assure engagement of the lock bolt.

 

Pongee Industries Co., Ltd is the leading electric lock series manufacturer in Taiwan. They provide electric deadbolt, electric drop bolt with various sizes to meet different demands of clients. For more details about electric deadbolts, RFID modules, UHF RFID readers etc., welcome to send inquiry to Pongee!

 

 

Article Source: http://www.eurohotelocks.com/?p=1511

What is RFID?

 

Radio-frequency identification device is a technology that retrieves the status and presence of a thing to which it is attached to remotely. These devices will track the objects automatically and sends the embedded information to the processors.

 

Typical components of RFID system

 

An RFID system contains an RFID tag, RFID reader, RFID antenna, and RFID package.

 

RFID tag is attached to the item that needs to be tracked and identified.

 

RFID antenna will detect the RFID tag when it comes in range.

 

RFID reader reads the RFID tags and authenticates its presence.

 

RFID package contains the server and software and transmits the information to all other applications.

 

Application of RFID systems

 

To simplify, RFID systems do the same function as of a BAR-CODES, but when it comes to applications they are widely spread as RFID systems doesn’t need to maintain contact with the scanners as in case of BAR-CODE. High Frequency RFID systems doesn’t necessarily to be appear in the line of sight, especially such are applied for livestock tracking, Missile tracking, automobile tracking through assembly lines and most importantly in case of vehicle tracking.

 

Security potential

 

Increasing security measures through CCTV cameras has already outdated, the latest technology implies to the usage of RFID readers wherever the security is needed along with authentication.

 

They can be installed in a library, home, and elsewhere domestically to secure the important files, books, and expensive things, so that even when they are found missing they can be easily detected with the help of local servers that are giving location information.

 

They can also be placed in a vehicle, thanks to their non-contact readable characteristic feature as the vehicles can be tracked along the route as they can use the location provided by the nearest GSM signal boosting towers and thus one can keep notice of their vehicles.

 

The size of the smallest developed RFID is 0.05mm × 0.05mm size and the average size would be around 3mm x 3mm. As we go cheaper the size will be increased consistently. Their dimensions make them invisible to see which a plus point in terms of security measures is.

 

Evercom Communication Technology Co., Ltd. is the professional company of specializing in kinds of antennas. If you are interested in learning more details about RFID antenna and other antennas, welcome to visit Evercom’s website to see what antennas they can offer you.

 

 

Article Source: http://EzineArticles.com/8431202

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Whether you’re looking to purchase a new treadmill or looking to update an existing one, knowing about which kind of motor to look for is vital to the success of your treadmill use. The motor is the main hub and carries the most weight mechanically. They vary in their abilities and capacities and are not all alike. It is essential to consider a few different variables with its motor before you make your treadmill purchase. This will ensure that you will bring the right treadmill home that is best-suited for your lifestyle and fitness goals.

 

Aside from the user, the motor does the most work in the treadmill. It is imperative that quality be assessed for long-term use, especially for more serious treadmill users. Poor quality motors are likely to overheat and require unnecessary repairs. The best way to check if your motor is a good quality motor is by checking the manufacturer warranty. A high-quality motor will have a longer warranty period and is a safer investment. In almost all of our treadmill reviews, we help you by giving the horsepower of the motor and by using the information below can determine if it is best suited for what you would use it for. One company that is known for high quality treadmill motors are Sole treadmills. They deliver a great product and stand behind it.

 

When it comes down to the nuts and bolts of the matter, treadmill motors are not wholly difficult to understand. Treadmill motor energy is measured in horsepower (HP) and can be sorted into three different rating systems:

 

  1. Peak Duty:

Generally the weakest. “Peak” stands for the peak horsepower that the treadmill will reach and no more.

  1. Treadmill Duty:

In-between peak and continuous

  1. Continuous Duty:

The highest rank. The number associated will describe how much power is maintained throughout the workout.

 

While many motors will claim to be of identical horsepower, it is pertinent to note that every motor is not built the same. Cheaper prices mean that the product consists of poorly made parts. Do not be swayed solely by low prices. A treadmill that originally cost $1000 or more is likely to possess a durable motor. Less expensive models are not likely to have a reliable motor installed.

 

Assess what kind of use the treadmill will predominantly be used for. The degree of exercise must be taken into account to make sure your treadmill motor reflects your lifestyle. Certain levels of exercise require specific amounts of horsepower; will it be for walking, jogging, running, or all three? Consider the following:

 

  • For walkers: a 2.0 horsepower continuous duty motor will suffice
  • For joggers: 2.5 horsepower continuous duty should be the minimum
  • For runners: 3.0 horsepower continuous duty or higher

 

Also note that if any of the users of the treadmill weigh over 200 pounds, HP should be increased by .5 for proper support, no matter the fitness goals. This means the HP should be at least 2.5 HP for walkers, 3.0 for joggers, and 3.5 for runners. Such precaution will extend the life of your motor.

 

As for sound, note that motors employing direct current (or known as DC) cause less noise compared to motors that use alternate current (also known as AC). Remember this when deciding where to place your treadmill, especially if you watch the television while you walk or run, or if the treadmill will be in a high traffic area of the home.

 

Hsiang Neng DC Micro Motor Manufacturing Corporation is the professional manufacturer of DC treadmill motor. If you want to obtain more information about treadmill motor or other actuator motor, welcome to visit the website of Hsiang Neng to see what excellent products they can offer you!

 

 

Article Source: http://www.treadmillreviews.net/treadmill-motors-what-you-need-to-know/

Choosing the right gateway or router isn’t all there is to successful mobile networking. Signal quality is essential and this can only be guaranteed by picking the right 3G or 4G LTE antenna and solutions.

 

Selecting the right antenna

When selecting an antenna the following considerations need to be made:

 

Where will the antenna need to be situated?

If outside then the antenna will need the appropriate IP rating to ensure it is protected against dust and water. If inside then it will need to be of a suitable size.

 

What application is the antenna being used for?

Different applications require different types of antennas, for example WiFi and GPS will require their own antennas in addition to cellular antennas.

 

What environment is the antenna being placed in?

For example, vehicular or industrial locations will require an antenna that is suitably ruggedized with the appropriate fixtures.

 

What is the quality of the signal in the intended location?

If the signal quality is poor then a high gain external antenna may suit it best.

 

What frequency band are you using?

Most high quality antennas cover a wide range of frequencies, but some cheaper antennas are only suitable for one type of connectivity, e.g. 2G, 3G or 4G.

 

How visible will the antenna be?

If it is highly visible in a prominent location then it may be important that it is aesthetically suitable.

 

Where and how does the antenna need to be fixed?

Different locations require for the antenna to be attached in different places, for example on a window, wall or ceiling, and will therefore require different types of fixtures, for example screw-on, stick-on or magnetic.

 

After these questions have been addressed, the process of selecting the correct 4G LTE antenna can begin.

 

Established in 1993, Evercom Communication specializes in manufacturing 4G LTE antennas. The new next generation of in-vehicle connectivity through 4G LTE solution can be monitored and managed remotely from the cloud. For more details, welcome to visit Evercom’s website to see what 4G LTE antenna series products we can offer you!

 

 

Article Source: https://www.westbaseuk.com/news/antennas-for-4g-lte-networking-the-making-or-breaking-of-a-solution/

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What Is a Proximity Reader?

On June 19, 2017, in Electronic Goods, by Lambert

If you are in the process of updating your home’s or business’s security system or if you never had such a system and you are planning to invest in one, there are probably a lot of industry terms you don’t understand very well. That is why, in this article, we are going to talk about two important parts of any security access system, the proximity card and the proximity reader.

 

Proximity cards, also referred to as prox cards, are different than the magnetic stripe cards, because they do not need to be inserted into the reader device to grant access in the secured area. We say “grant access” because the majority of proximity cards and proximity readers are used as a part of home or business security system. Other uses include library cards, contactless payment systems or in public transit fare. Proximity cards are practical due to the fact that they can easily be read through a wallet or a purse.

 

There are two main types of proximity cards: passive and active. Passive prox cards have a limited range and are widely used to grant access in office buildings. Active cards, also called vicinity cards, have a greater range (150 meters), due to the fact that they use and internal lithium battery. They can be used to easily access courtyards from inside of a vehicle or from automated toll collection.

 

Now, in case you were wondering “What is a Proximity Reader?” they are devices that can store details about the identity of the cards holders, granting them access to otherwise restricted areas. This system is similar to the “chip and PIN” bank cards, with the difference that the proximity reader grants access using radio frequencies and does not need actual insertion of the card. Also, they offer more security to their holders, due to the fact that they are harder to copy. Another great advantage of these readers is the fact that they are quite sturdy and do not need any maintenance.

 

Another term you might encounter when browsing for this type of access system in “Contactless Smart Card”, which is basically the same thing, with the difference that they use advanced methods of data encryption and authentication, meaning that they offer a higher level of security. Besides this general information, there are various technologies that are used in the manufacture of proximity cards and readers.

 

If you are planning to invest in such a system, you must know that the prices are very different from one product to another. For example, the price for a single card ranges from $2 to $200, while for the proximity reader you can pay from $100 to $400.

 

Before making any purchase, we advise you to ask the advice of an experienced security technician, just to make sure that you choose the right system for your needs. The good news is that the majority of shops, even online ones, have an assistant which can help you make the right decision.

 

Pongee Industries Co., Ltd. is the manufacturer of proximity reader. If you are looking for the best proximity reader, don’t miss Pongee’s website, we can offer clients kinds of high quality products. Contact with Pongee to obtain further product information!

 

 

Article Source: http://EzineArticles.com/8665232

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Motors play an important part in lifting and running a device. They are limited to weight but high efficiency and power capacity motors can easily cover heavy weight situations. Brushless Motors are best used for quadcopters, multicopters and drones.

 

Choosing motors for copter projects is not an easy task, so for every selection technical specifications such as thrust, power and RPM is to be checked.

 

Generally, planning to prepare your own project for the first time, weight is to be considered then the thrust to lift the quadcopter. The thrust should be kept higher for proper lifting, flying and landing. According to general statistics, thrust should be kept twice the weight of the quadcopter.

 

Trust is kept perfect, too low might create difficulties to take off and too high become hard to control.

 

A light weight copter is more efficient and durable.

 

Additionally, the battery is also considered an important element for long life of quadcopter. Lithium polymer batteries are best suited for long run as they do not swell nor they heat up faster. Batteries should be charged when it reaches a minimum of 20 percent. Zero percent might lower the durability of the battery. Brushless DC motors accomplished high speed of 10000 RPM or above.

 

Brushless DC motor architecture sounds very simple and compact. A fixed armature is present in the brushless motor around which permanent magnets rotate. Brushless DC motors are best suited as they produce high torque to weight ratio, increased reliability, more torque per watt, reduced noise, no brush required, as long life, totally eliminates ionizing sparks from the commutator plus reduce electromagnetic interference. Brushless motor commutation is easily implemented using a microcontroller, analogue hardware or digital firmware by using an FPGA. Brushless commutation has greater flexibility, speed limiting, holding torque when stationary, micro stepped operation for slow or fine motion control.

 

Brushless motors cover a wide range of applications in the field of electronic devices which comprise of computer hard drives, DVD/CD players, refrigeration. They are also favorable to electric vehicles such as bicycle and hybrid vehicles. Users or learners can use brushless DC motor in various quadcopter, multicopter or drones adding additional accessories for a specific function. Copters help in remodeling, transferring load, surveillance, Videography and many more.

 

After improving its performance, again, both the coils are energized and further improved in a manner such that it pushes the rotor and energize the coils. Therefore, it results in increasing torque and power from the motor. This great achievement is seen in this motor and takes time for other type of motors to grab.

 

Rebeck Enterprise is the manufacturer of brushless DC motors. Our brushless DC motor, high efficiency can be applied to mechanical precision positioning. And the motor features long life time, high efficiency, low noise, low consumption, variable speed, and many more. Welcome to visit our website to learn further details about brushless DC motor, and feel free to send inquiry to Rebeck!

 

 

Article Source: http://EzineArticles.com/9220583

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What exactly is geo-mapping and aerial survey?

 

We believe that the future of aerial surveying is not fixed and static, but flexible and dynamic. It´s a great way to receive data for orthophotos, 3D models in high resolution with great accuracy. We also offer you an in-house flight planning software, suited for simple dealing with data and parameters.

 

Aerial survey is a great solution for various kinds of applications. It can be used to deal with challenging sites such as quarries, sand pits, landfills, coal stockpiles. When using the drones in order to create aerial maps, you can undoubtedly go places that conventional equipment cannot reach. Moreover, you acquire more safety for your surveying staff and save time and costs.

 

Advantages of aerial mapping

 

Connection of a drone and a very precise GPS receiver is one of the crucial areas of the future aerial mapping development. Another important feature is special software, suited for data processing and virtual map making. This software allows importing the data gathered by the precise GPS receiver. Each image is connected to a required data package, which is important for further georeferencing and coordinate system making.

 

A common UAV survey can typically produce up to 500 high quality images per square kilometer, at 1cm to 5cm resolution. In addition, the detail obtained from the individual imagery or orthorectified mosaics usually surpasses anything else what is presently accessible even from satellite or classical aerial photography.

 

Aerial mapping step by step

 

The first step of UAV mapping is always preparation. There you should define your requirements and flight parameters, such as altitude, airspeed, overlap and distances. In a next step is done the actual flight plan, including precise directions, amount, routes and such. As a next step is usually recommended to create control points for each hectar in order to achieve high accuracy geo-referencing. After that follow flight operations. Common recording while surface flight is performed at a 90° degree angle for capturing the images orientated straight down to the surface.

 

GPS coordinates are connected directly to the photo’s data, which allow processing the geo-referenced data in many GIS systems. After all that you can finally create 3D models and orthophotos. Conventional aerial photos are limited regarding their use in GIS because they are not true to scale. In order to create a scale correct photograph that can be accurately measured, an orthographic projection is definitely necessary, in which the view is straight down over every point in the photo. An orthographic photo can be really used to measure precise distances, for it is an accurate representation of the Earth´s surface.

 

Carbon-Based Technology, Inc. devoted in complete system design, integration, manufacturing, and global marketing of Unmanned Aircraft System. We not only can offer high reliability Unmanned System as a platform for “Intelligence Gathering”, but also can offer total solutions for various aspects. If you need further details about aerial mapping and UAVs, welcome to browse our website or contact with Carbon-Based directly!

 

 

Article Source: http://vespadrones.com/uav-mapping/

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Switching mode power supply (SMPS) is used in a range of applications as an efficient and effective source of power. This is in major part to their efficiency. For anybody still working on a desktop, look for the fan output in the central processing units (CPU). That’s where the SMPS is. SMPS offers advantages in terms of size, weight, cost, efficiency and overall performance. These have become an accepted part of electronic gadgets. Basically it is a device in which energy conversion and regulation is provided by power semiconductors that are continuously switching “on” and “off” with high frequency.

 

The different kinds

  • C. to D.C. Converter
  • Forward Converter:
  • Flyback Converter:
  • Self-Oscillating Flyback Converter
  • DC-DC converter

 

The primary power received from AC main is rectified and filtered as high voltage DC. It is then switched at a huge rate of speed and fed to the primary side of the step-down transformer. The step-down transformer is only a fraction of the size of a comparable 50 Hz unit thus relieving the size and weight problems. We have the filtered and rectified output at the secondary side of the transformer. It is now sent to the output of the power supply. A sample of this output is sent back to the switch to control the output voltage.

 

Forward converter

 

In a forward converter the choke carries the current when the transistor is conducting as well as when it’s not. The diode carries the current during the OFF period of the transistor. Therefore, energy flows into the load during both the periods. The choke stores energy during the ON period and also passes some energy into the output load.

 

Flyback converter

 

In a flyback converter, the magnetic field of the inductor stores energy during the ON period of the switch. The energy is emptied into the output voltage circuit when the switch is in the open state. The duty cycle determines the output voltage.

 

Self-Oscillating Flyback Converter

 

This is the most simple and basic converter based on the flyback principle. During the conduction time of the switching transistor, the current through the transformer primary starts ramping up linearly with the slope equal to Vin/Lp. The voltage induced in the secondary winding and the feedback winding make the fast recovery rectifier reverse biased and hold the conducting transistor ON. When the primary current reaches a peak value Ip, where the core begins to saturate, the current tends to rise very sharply. This sharp rise in current cannot be supported by the fixed base drive provided by the feedback winding. As a result, the switching begins to come out of saturation.

 

Basic working concept of a SMPS

 

A switching regulator does the regulation in the SMPS. A series switching element turns the current supply to a smoothing capacitor on and off. The voltage on the capacitor controls the time the series element is turned. The continuous switching of the capacitor maintains the voltage at the required level.

 

Design basics

 

AC power first passes through fuses and a line filter. Then it is rectified by a full-wave bridge rectifier. The rectified voltage is next applied to the power factor correction (PFC) pre-regulator followed by the downstream DC-DC converter(s). Most computers and small appliances use International Electrotechnical Commission (IEC) style input connector. As for output connectors and pinouts, except for some industries, such as PC and compact PCI, in general they are not standardized and are left up to the manufacturer.

 

Why SMPS

 

Like every electronic gadget, switching mode power supplies also involve some active and some passive components. And like every of those gadgets, it has its own advantages and disadvantages.

 

Let’s start with why you should go for a SMPS

 

  • The switching action means the series regulator element is either on or off. Very high efficiency levels are achieved as very little energy us dissipated as heat.
  • As a result of the high efficiency and low levels of heat dissipation, the switch mode power supplies can be compact.
  • Switch mode power supply technology also provide high efficiency voltage conversions in voltage step up or “Boost” applications and step down or “Buck” applications.

 

Then there’s the bad set

 

  • The transient spikes due to the switching action can migrate into other areas of the circuits if not properly filtered. These can cause electromagnetic or RF interference affecting other nearby items of electronic equipment, particularly if they receive radio signals.
  • To ensure that a SMPS performs as per the required specification can be a bit difficult. The ripple and interference levels are particularly tricky.
  • The costs of a switch mode power supply is calculates before designing or using one. Additional filtering further adds to the cost.

 

What would the future hold?

 

In the future, we could have more efficient SMPS aimed at a better converter doing the most effective conversion process. The focus areas for designers in making SMPS efficient would be:

 

  • Higher output power
  • Achieving higher current output and low voltage
  • Increasing power density
  • Using switching device like Schottky diode

 

Hon-Kwang Electric specialized in manufacturing switch mode power supply and related products. We provide series of switching power supplies to meet different demands of you. If you are interested in learning more details about switching mode power supply, please feel free to contact with Hon-Kwang.

 

Article Source: http://electronicsforu.com/resources/learn-electronics/smps-basics-switched-mode-power-supply

When it comes to overcurrent protection of electronic equipment, fuses have long been the standard solution. They come in a wide variety of ratings and mounting styles to fit virtually any application. When they open, they completely stop the flow of electricity, which may be the desired reaction; the equipment or circuit is rendered inoperable, which draws the user’s attention to what may have caused the overload condition so that corrective action can be taken.

 

Nevertheless, there are circumstances and circuits where auto-recovery from a temporary overload without user intervention is desirable. Positive temperature coefficient (PTC) thermistors – also called polymeric positive temperature coefficient devices (PPTCs) or resettable fuses – are an excellent way of achieving this type of protection.

 

Ceramic PTCs are also widely available through possess different operating characteristics including greater internal resistance, higher ambient heat tolerance, and higher voltage ratings. As they are typically used within high ambient heat areas including heating equipment applications not common to many electronics requirements, they were not factored within the scope of this article.

 

How a PTC works

 

A PTC resettable fuse consists of a piece of polymer material loaded with conductive particles (usually carbon black). At room temperature the polymer is in a semi-crystalline state and the conductive particles touch each other, forming multiple conductive paths and providing low resistance (generally about twice that of a fuse of the same rating).

 

When current passes through the PTC it dissipates power (P = I2R) and its temperature increases. As long as the current is less than its rated Hold Current, IHOLD, the PTC resettable fuse will remain in a low-resistance state and the circuit will operate normally. When the current exceeds the rated Trip Current, ITRIP, the PTC heats up suddenly. The polymer changes to an amorphous state and expands, breaking the connections between the conductive particles. This causes the resistance to increase rapidly by several orders of magnitude and reduces the current to a low (leakage) value just sufficient to keep the PTC in the high-resistance state – generally from around tens of milliamps to several hundred milliamps at rated voltage (Vmax). When the power is shut off the device cools down and returns to its low-resistance state.

 

Like a fuse, a PTC is rated for the maximum short circuit current (IMAX) it can interrupt at rated voltage. IMAX for a typical PTC is 40A, and may reach 100A. Interrupting ratings for fuses of the sizes that may be used in the sorts of applications we are considering here can range from 35 to 10000 amperes at rated voltage.

 

The voltage rating for a PTC is limited. PTC resettable fuses for general use are not rated above 60V operating voltage (there are PTCs for telecom application with 250V and 600V interrupting voltage, but their operating voltage is still 60V); surface-mount and small cartridge fuses are available with ratings from 32V to 250V or more.

 

The operating current rating for PTCs ranges up to about 9A, while the maximum level for fuses of the types considered here can exceed 20A, with some available to 60A.

 

The useful upper temperature limit for a PTC is generally 85°C, while the maximum operating temperature for thin-film surface mount fuses is 90°C, and for small cartridge fuses is 125°C. Both PTCs and fuses require derating for temperatures above 20°C, although PTCs are more sensitive to temperature (Fig.2). When designing in any overcurrent protective device, be sure to consider factors that may affect its operating temperature, including the effect on heat removal of leads/traces, any air flow, and proximity to heat sources. The speed of response for a PTC is similar to that of a time delay fuse.

 

Common PTC applications

 

Much of the design work for personal computers and peripheral devices is strongly influenced by the Microsoft and Intel System Design Guide which states that “Using a fuse that must be replaced each time an overcurrent condition occurs is unacceptable.” And the SCSI (Small Computer Systems Interface) Standard for this large market includes a statement that “… a positive temperature coefficient device must be used instead of a fuse, to limit the maximum amount of current sourced.”

 

PTC resettable fuses are used to provide secondary overcurrent protection for telephone central office equipment and customer premises equipment, alarm systems, set top boxes, voice over IP (VOIP) equipment and subscriber line interface circuits (SLICs). They provide primary protection for battery packs, battery chargers, automotive door locks, USB ports, loudspeakers and power over Ethernet.

 

SCSI Plug and Play applications that benefit from PTCs include both the mother-board and the many peripherals that can be frequently connected to and disconnected from the computer ports. The mouse, keyboard, printer, modem and monitor ports represent opportunities for misconnections and connections of faulty units or damaged cable. The ability to reset after correction of the fault is particularly attractive.

 

A PTC resettable fuse can protect disk drives from the potentially damaging overcurrent resulting from excessive current from a power supply malfunction.

 

PTC resettable fuses can protect power supplies against overloading; individual PTCs can be placed in the output circuits to protect each load where there are multiple loads or circuits.

 

Motor overcurrent can produce excessive heat that may damage the winding insulation and for small motors may even cause a failure of the very small diameter wire windings. The PTC will generally not trip under normal motor start up currents, but will act to prevent a sustained overload from causing damage.

 

Transformers can be damaged by overcurrent caused by circuit faults, and the current limiting function of a PTC can provide protection. The PTC is located on the load side of the transformer.

 

Fuse or PTC?

 

The following procedure will help in selecting and applying the correct component. Help is also available from device suppliers. For unbiased advice it is wise to look for a company that offers both fuse and PTC technology.

 

  1. Define the circuit operating parameters. Consider the following: normal operating; current in ampere; normal operating voltage in volts; maximum interrupt current; ambient temperature/rerating; typical overload current; required opening time at specific overload; transient pulses expected; resettable or one-time; agency approvals; mounting type/form factor; typical resistance (in circuit).

 

  1. Select a prospective circuit protection component.

 

  1. Determine the opening time at fault. Consult the Time-Current (T-C) Curve to determine if the selected part will operate within the constraints of the application.

 

  1. Verify ambient operating parameters. Ensure that the application voltage is less than or equal to the device’s rated voltage and that the operating temperature limits are within those specified by the device

 

  1. Verify the device’s dimensions. Compare the maximum dimensions of the device to the space available in the application.

 

  1. Test the selected product. Independently test and evaluate suitability and performance in the actual application.

 

Zonkas is the professional manufacturer of capacitor, inductor and transformer. Our main products including: various inductors, transformers, Safety Capacitor (Y1, Y2, X1, X2), Ceramic Capacitor, Film Capacitor and Electrolytic Capacitor. If you need more information about PTC resettable fuses or other capacitors, welcome to visit our website or contact with Zonkas directly!

 

 

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