PTC Thermistors: Positive Temperature Coefficient

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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Overview of Power Capacitors

What are they?

 

Power capacitors work by acting as a reserve power bank; they store the charge rather than being the source of power such as the battery. When you are listening to your music, and playing a heavy sub-bass note, the power will draw from the capacitor rather than from the battery so to ensure that the rest of the car will not be starved of power i.e. the headlights dimming. It will act as a buffer so that that the power being delivered to the amplifiers will not drop below the recommended voltages and be steady therefore reducing the risk of damage to the components.

 

So what power capacitor to choose?

 

After doing a bit of research, the general rule seems to be 1 farad per 1000 watts of power that your system is running at. So using that, a 1.5 farad power capacitor should be ideally suited to a 1500 watt system. There is a large selection of power capacitors available out there, for example, this power capacitor is a 2 farad power capacitor designed for smaller systems, this is not to say however that it will have a reduction in performance, however for those systems that require more power, a power capacitor with a higher farad will be able to deliver for longer and will usually be of a higher build quality.

 

How to install the capacitor

 

Ideally the capacitor needs to be installed as close to the amplifiers as possible. The capacitor requires a 12 volt positive from the battery and a separate ground, to the amplifier; so that the 12 volt positive is ‘inline’ with the terminal from the battery and the amplifier. The amplifier 12 volt positive is then taken from the capacitor while the amplifier is usually grounded separately as it is important to use as short a ground cable as possible to reduce any potential ground interference.

 

When you need to consider other alternatives

 

Power capacitors will not always be of help when you are listening to music, if the lights for example dim down, and stay dim, this indicates there is a deficiency of power and there are other methods of solving the problem, it could potentially be that the battery is not able to generate a charge sufficient enough to meet the demands, so installing a higher cranking battery is usually the common solution however it is possible that upgrading “The Big Three” may also solve the issue(see below for more details). It is also important to check that the current alternator can produce a charge that will be sufficient with a larger battery.

 

‘The Big Three’

 

The big three is a popular upgrade. It consists of upgrading three wires in the car to ones that are much thicker. As a result of using much thicker wire, more current is allowed to flow through; hence the overall effect seen will be that the voltage running through the car will be higher. The three wires that are upgraded are the wire from the alternator to the battery, the engine ground to the chassis and the battery ground to the chassis. It is common, but not always, that people will choose 0 gauge power wire when going about the big three upgrade. This is vital again to ensure that the voltage delivered to the amplifiers does not drop so low that the risk of damage is possible.

 

Conclusion

 

So in conclusion, there is no hard or fast answer to if a capacitor is necessary or not. However capacitors may have benefits if used appropriately. There are large selections of capacitors; some come with digital volt meters, distribution blocks etc., while others are purely chosen for aesthetic pleasure, I myself went for a 4 farad power capacitor with a built in digital volt meter with an LCD display so that it was something I was able to display and looks pretty damn cool.

 

If you need more details about power capacitors and capacitor supplier, welcome to visit our website and feel free to send inquiries to YUHCHANG – the outstanding and professional power capacitor manufacturer in Taiwan.

 

 

Article Source: http://EzineArticles.com/expert/Neil_Patel/563675

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How Capacitors Work

Capacitors, which were previously known as condensers, are electrical components that store electric charge temporarily. Although capacitors may come in various shapes and sizes, they all have one function in common, storing electrical charge. The capacitor has two terminals that are separated by a non-conducting substance called dielectric. The dielectric can be made of film, paper plastic or air whereas the terminals can be made of aluminum or other conductive metals. One can even make capacitors at home by using two pieces of aluminum foil and a piece of paper. Although it would not be a good capacitor, it would still be able to function.

Although any non-conductive material can be classified as dielectric, only specific materials are used to construct capacitors depending how it will be applied. The dielectric can dictate what type of capacitor it would be and its application. The type and size of the dielectric used would determine the application of the capacitor. Some capacitors may be ideal for high frequency applications whereas others may be better at high voltage applications. They can be used for a variety of applications ranging from torch lights to huge capacitors that can power buses.

Capacitors that use air as a dielectric material in them can be used for radio tuning circuits. Capacitors using Mylar can be commonly found in timer circuits such as alarm clocks and glass and are often used as a dielectric material in capacitors that require high voltage applications. Applications that have high frequency such as x-ray or MRI make use of ceramic capacitors.

The amount of charge that a capacitor can store, which can also be called its capacitance, is measured in units called farads. A capacitor unlike a battery can take only a fraction of a second to completely discharge. A battery may however take minutes to do so. Due to this feature of capacitors, they are often used in the electronic flash on cameras. When you click a picture the flash come and goes off immediately. This is a good example of a capacitor discharging all its stored energy in a fraction of a second. When the flash is not clicked, the battery charges it up and it discharges this energy when a picture is clicked using flash. This however can be dangerous as capacitors such as those in television sets can contain large amount of charge. Therefore, if you were to open your TV set and touch the fully charged capacitor it could kill you.

Capacitors have definitely improved electronic devices tremendously and as well as aided in the advancement of technology greatly. However, when using electronic devices that have capacitors that can store a huge charge, one should always be very careful.

To learn more about how capacitors work or find where you could purchase them, you can log on to our website at thegreenbook.com

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