SPRAGUE Sprague Electric was started by Robert C. Sprague in 1926 in Quincy, Massachusetts, as Sprague Tantalum capacitor Company. Sprague is credited with inventing a tone control device that greatly improved the sound of radios.
In 1929, the company decided to move to North Adams, Massachusetts. The move was completed in 1930. At its peak, Sprague Electric employed 12,000 people worldwide, including over 4000 people in North Adams alone in five separate sites. Marshall Street,” was composed of 23 different buildings, all linked by covered overpasses and tunnels.
In the mid ’60s, Sprague had plants in Scotland, France, Italy and Japan, in addition to multiple locations in the USA. In 1981, Penn Central acquired all the stock of GK Technologies. In 1985, the Sprague North Adams operations were closed. In 1992, Vishay acquired the tantalum capacitor operations of Sprague Electric Company, while other product lines were spun off. Tantalum Capacitors Sprague is credited with developing the first wet tantalum capacitor in the late 1940s.
At the time, these capacitors used tantalum foil as an electrode and dielectric medium with a sulfuric acid-based solution as an electrolyte. Other types were further developed using tantalum powder enclosed in a silver case. The solid tantalum capacitor was invented at Bell Labs in 1956. This type uses manganese dioxide particles as an electrolyte. This was developed for the NASA space shuttle program. Sprague, Tansitor, and Mallory received a number of patents for tantalum capacitors. The 195D, a cost-efficient version, was developed by using plated terminations deposited by a batch process.
Its unique cathode system provided the highest capacitance per unit volume. It uses patented technology involving leadframeless terminations, enabling increased volumetric efficiency in portable electronics. This technology was greatly improved with the 298D. Tantalum capacitors are electrolytic capacitors which use tantalum metal for the anode. They are polarized capacitors with superior frequency and stability characteristics. Tantalum capacitors are made with capacitance values ranging from 1nF all the way to 72mF and they are much smaller in size than aluminum electrolytic capacitors of the same capacitance. The voltage rating for tantalum capacitors varies from 2V to more than 500V.
ESR of aluminum electrolytic capacitors, which allows for larger currents to pass through the capacitor with less heat generated. Tantalum electrolytic capacitors are exceptionally polarized devices. While aluminum electrolytic capacitors, which are polarized as well, might survive a briefly applied reverse voltage, tantalum capacitors are very sensitive to reverse polarization. If a reverse polarity voltage is applied, the dielectric oxide breaks down, sometimes forming a short circuit. This short circuit may later cause thermal runaway and destruction of the capacitor.
It should be noted that tantalum capacitors usually have their positive terminal marked, in contrast to aluminum electrolytic capacitors, which have their negative terminal marked on the casing. Tantalum capacitors have a potentially dangerous failure mode. In case of voltage spikes, the tantalum anode may come in contact with the manganese dioxide cathode, and if the energy of the spike is sufficient it may start a chemical reaction. This chemical reaction produces heat and is self-sustaining and may produce smoke and flame.
Tantalum electrolytic capacitors, just like other electrolytic capacitors, are consisted of an anode, some electrolyte and a cathode. The anode is isolated from the cathode so only a very small leakage DC current may flow through the capacitor. The anode is made of pure tantalum metal. The metal is ground into a fine powder, and sintered into a pellet at high temperatures. This forms a very porous anode with a high surface area.
The anode is then covered with a layer of insulating oxide, which acts as a dielectric. This step must be precisely controlled to reduce tolerances and ensure correct capacitance values as the extent of oxide growth determines the dielectric thickness. Electrolyte is added to the anode by means of pyrolysis in the case of solid tantalum capacitors. Solid tantalum capacitors are then dipped into a special solution and baked in an oven to produce a manganese dioxide coat. The process is repeated until a thick coating is present on all internal and external surfaces of the pellet. Finally, the pellet used in solid tantalum capacitors is dipped into graphite and silver to provide a good cathode connection.
Applications using tantalum capacitors take advantage of their low leakage current, high capacity and long term stability and reliability. For example, they are used in sample and hold circuits which rely on low leakage current to achieve long hold duration. They are also commonly used for power supply filtering on computer motherboards and cell phones due to their small size and long term stability, most often in surface mount form. Capacitance Value The capacitance values for some capacitors are printed directly on the component. This is true of larger capacitors with values of 1 μF or higher, if for no other reason that their larger physical size allows the manufacturer to directly print the value on the component. But for other capacitors things aren’t always so simple.
01 μF disc variety, use a common three-digit marking system to denote capacitance and tolerance. The numbering system is easy to use, if you remember it’s based on picofarads, not microfarads. To make the conversion, move the decimal point to the left six spaces: 100000 becomes . Note that values under 1000 picofarads do not use this numbering system. Like resistors, the tolerance of the capacitor indicates how close the printed value meets reality. That means the capacitor, which is rated at .
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1 μF, might be as much as 80 percent higher or 20 percent lower. See below for a list of letter-style tolerance codes. This mark uses three characters to indicate the temperate tolerance, and maximum variation within the stated temperature range. A table of EIA tolerance markings is shown later in this app note. Table 1 provides a quick glance at how several common capacitor number markings convert to their μF microfarad equivalents. Dielectric Breakdown Voltage Value The dielectric breakdown voltage is only specified for certain capacitors. Sometimes, the letters WV are used after the voltage rating.
You should not use the capacitor with voltages that exceed this value. On capacitors without a breakdown voltage printed on them you must estimate the value based on the type of dielectric it uses. This is an advanced topic and not covered in this book, and nevertheless, seldom comes up in electronics for robotics because most circuits use 12 volts or less. Only a few capacitors are designed with breakdown voltages less than this, and these are primarily used for such tasks as temporary battery backups.
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If a capacitor is polarized, it is extremely important that you follow the proper orientation when you install the capacitor in the circuit. Other components in the circuit could also be damaged. The first is used with small ceramic capacitors, and appears as a single letter. Mica minerals are very stable electrically, chemically and mechanically. Because of its specific crystalline structure binding, it has a typical layered structure. This makes it possible to manufacture thin sheets in the order of 0. The most commonly used are muscovite and phlogopite mica.
The first has better electrical properties, while the second has a higher temperature resistance. Mica is delved in India, Central Africa and South America. Silver mica capacitors use mica as the dielectric. They have great high-frequency properties due to low resistive and inductive losses, and are very stable over time. This is much better than practically all other types of capacitors.
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Mica capacitors are very stable and very accurate. Their capacitance changes little over time. This is due to the fact that there are no air gaps in the design which could change over time. Also, the assembly is protected from moisture and other effects by an epoxy resin. This means that outside effects such as air humidity do not affect mica capacitors. Not only is their capacitance stable over time, it is also stable over a wide temperature, voltage and frequency range.
Their characteristics are mostly frequency-independent, which allows for their use at high frequency. These superior characteristics come at a price: silver mica capacitors are bulky and expensive. The construction of silver mica capacitors is relatively simple. Old clamped mica capacitors used thin sheets of mica layered with thin sheets of silver. These layers were clamped and electrodes were added. However, due to physical imperfections in both mica and silver layers, there were small air gaps present which limited the precision of clamped mica capacitors. Post-WW2 silver mica capacitors are made by plating the silver directly on the surface of mica and layering these to achieve the desired capacitance.
After the layers are assembled, electrodes are added and the assembly is encapsulated. Ceramics or epoxy resins are used as encapsulation material in order to protect the silver-mica capacitor from outside effects such as moisture. Silver mica capacitors have a relatively small capacitance value: usually between a few pF, up to a few nF. The largest capacitance mica capacitors can reach values of 1µF, although these are uncommon. Silver mica capacitors are usually rated for voltages between 100 and 1000 volts, although there are special high-voltage mica capacitors designed for RF transmitter use which are rated at up to 10 kV. Silver mica capacitors are used in applications which call for low capacitance values and high stability, while exhibiting low losses.
Their main use is in power RF circuits where stability is of utmost importance. Silver mica capacitors are used in high frequency tuned circuits, such as filters and oscillators. They are sometimes used in pulsed applications as snubbers. Although they were once very popular as quality capacitors, nowadays they are increasingly being replaced by other types of capacitors due to their size and cost, which can reach several USD a piece. In low power RF applications, a good replacement for mica capacitors are ceramic capacitors. If capacitance tolerances and low losses are an important factor, Class 1 ceramic capacitors can be used, since these capacitors have similar tolerances at a fraction of the price. In some applications, silver mica capacitors are still indispensable.
For example, circuit designers still turn to mica capacitors for high-power applications such as RF transmitters. Another application where silver mica remains widely used are high-voltage applications, due to mica’s high breakdown voltage. Over time, a series of standard capacitor values have evolved, just as with resistors and inductors. Capacitors are available in a huge range of package styles, voltage and current handling capacities, dielectric types, quality factors, and many other parameters.
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Still, they largely hold to this range of values. Often, complex combinations are used in order to satisfy multiple requirements such as handling large voltages while still providing the correct amount of capacitance. If it is necessary to provide occasional tuning of a circuit, then it is necessary to use a variable capacitor. These are the most commonly available capacitor values. Tolerances are highly dependent on dielectric and package type. RF Cafe began life in 1996 as “RF Tools” in an AOL screen name web space totaling 2 MB.
Physically small capacitors are especially difficult to read, due to the limited space available for printing. The information in this article should help you read almost all modern consumer capacitors. Don’t be surprised if your information is printed in a different order than the one described here, or if voltage and tolerance info is missing from your capacitor. Most large capacitors have a capacitance value written on the side. Slight variations are common, so look for the value that most closely matches the units above. For example, “MF” is just a variation on “mf.
It is definitely not a megafarad, even though this is the official SI abbreviation. This is just another abbreviation for farad. For example, “mmfd” is the same as “mmf. Beware single-letter markings such as “475m,” usually found on smaller capacitors. Some capacitors list a tolerance, or the maximum expected range in capacitance compared to its listed value. This isn’t important in all circuits, but you may need to pay attention to this if you require a precise capacitor value. This is the maximum voltage the capacitor is designed to handle.
If there is no symbol at all, reserve the cap for low-voltage circuits only. If you are building an AC circuit, look for a capacitor rated specifically for VAC. Do not use a DC capacitor unless you have an in-depth knowledge of how to convert the voltage rating, and how to use that type of capacitor safely in AC applications. If you see one of these next to a terminal, the capacitor is polarized. Write down the first two digits of the capacitance. Older capacitors are less predictable, but almost all modern examples use the EIA standard code when the capacitor is too small to write out the capacitance in full.
If one of the first two characters is a letter, skip down to letter systems. If the first three characters are all numbers, continue to the next step. Use the third digit as a zero multiplier. If the third digit is 8, multiply by 0.
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If the third digit is 9, multiply by 0. For example, 4R1 means a capacitance of 4. Replace this letter with a decimal point. 61 nF, and 5u2 means 5. A code like “1A253” is actually two codes. 1A tells you the voltage, and 253 tells you the capacitance as described above.
Ceramic capacitors, which are usually tiny “pancakes” with two pins, typically list the tolerance value as one letter immediately after the three-digit capacitance value. This letter represents the tolerance of the capacitor, meaning how close the actual value of the capacitor can be expected to be to the indicated value of the capacitor. If you see no tolerance listed, assume this as the worst case scenario. Many types of capacitors represent the tolerance with a more detailed three-symbol system. The second symbol shows maximum temperature. The third symbol shows variation in capacitance across this temperature range. One letter codes are abbreviations of one of the common values above.
For an estimate of other, less common codes, look at the first digit. Old capacitors or capacitors made for specialist use may use different systems. If there is no code but a series of colored bands or dots, look up the capacitor color code. If I don’t find a 470 uF-25v, what are the substitutes that can be used?
I have a polyester film capacitor with number 2A224J. I have a small round capacitor with some numbers on it but no units. It has a 7, followed by a small space and a 3. A second line says 100, and a third line says 25A. What capacitance and voltage is this?
How do I read the value of a capacitor that looks like a resistor? Put it on a multimeter with both OHMS range and capacitance. Stick close to the 50 ufd value. Run caps are used to provide phase shift for windings on motors so deviation from the designed value will affect the motor’s performance. Be sure to choose one rated as a RUN capacitor and not a start capacitor. Run caps have lower internal losses. Electrical supply houses usually stock both these kinds, as they are a frequently replaced item for motors.
Can I replace a 1000uf 35v cap with a 1200uf 35v cap? If the capacitor is in a filter stage of a rectifier, you may use 1200uf. But I suggest the same uf value. Can a line capacitor be used to replace a surface mount capacitor?