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Royal OHM Resistors – Electronics For You

Resistors are the most commonly used electronic and electric components. Their applications are so numerous and diverse that they are present in product portfolios of a great deal of specialist manufacturers. One of them is Royal OHM, whose assortment is focused almost entirely on resistors – from precision electronics components to high-power machinery parts.

Many TME customers are manufacturers of electronic and electrotechnical equipment. Therefore, we are well aware of the importance of ensuring the wide availability of basic components. At the same time, we make sure that the products come from a range of tried-and-tested suppliers and offer good value for money. For this very reason, we recommend solutions marketed by Royal OHM, a company that supplies resistors suitable for all popular applications.

This article covers the following issues:

  • New method of labelling SMD resistors manufactured by Royal OHM
  • Resistors for automotive industry
  • Precision resistors with a very low thermal coefficient
  • Resistors for high-current and high-power applications
  • Resistor network types and applications

New symbols and parametrisation

Firstly, note the changes introduced in Royal OHM component symbols. This applies to the majority of SMD resistors offered by TME. For a number of years, the manufacturer’s range of products was divided into standard- and enhanced-power components – yet, it turned out that in the case of several values certain product symbols were duplicated. Therefore, resistors are now labelled in line with a modified convention. See the decoding example below:

The first characters specify the component size. These are set in line with the most commonly applied standard, i.e. using the imperial system of measurement units to describe product dimensions. The first two and last two digits denote, respectively, the length and width of the item in hundredths of an inch.

Note that that the TME product catalogue includes SMD resistors belonging to different groups, where the first characters specify the series name (i.e. their names are more descriptive for customers’ convenience [e.g. CQ1206-348R-1%]). In such cases, the Royal OHM product symbol contains two letters denoting the product series (character 1 and 2) plus two digits denoting their size (character 3 and 4). The latter assumes the following values (where “xx” stands for, e.g. “CQ”, “HP”, etc.):

Characters 5–6

These two characters specify the component power. The TME product catalogue includes resistors rated from 50 mW to 3 W (2 W and 3 W resistors are included in the SP and HP series, where the designation method is different). See the table below for character combinations denoting the power rating of the majority of the SMD resistors from Royal OHM:

Character 7

Here, the component tolerance rating is specified, and its value can be ±0.1% (letter B), ±0.5% (letter D), ±1% (F), ±2% (G) and 5% (J).

Characters 8–11

These four consecutive characters denote the resistance rating. Here, one of the two character combinations can be applied. For components with the 5% tolerance rating, the first digit is always “0”, the next two digits specify the value base in ohms (Ω), and the last digit shows the number of zeros (J stands for -1, and K stands for -2, therefore, the base must be divided by 10 or 100). The situation is similar for other tolerance ratings, but here all 3 digits at the beginning of the sequence refer to the primary value.

Other characters

The remaining characters in the product symbol specify the component packing method and any special properties of the product. Practically all Royal OHM product symbols end with an “E”, which means that the products are lead-free.

Royal OHM resistors

The range of Royal OHM products available in the TME product catalogue is divided into four component types: SMD and THT resistors, power resistors and resistor networks. They are available in typical and strictly standardised enclosures, so they can be used in mass-production processes. See below for an overview of these main product groups and their general characteristics.

SMD resistors

The SMD resistors are among the most commonly used electronic components and constitute a staple part of the Royal OHM product range. These components are housed in 0201–2512 enclosures. Apart from standard power ratings (tenths of watts), the manufacturer also provides 1–3 W components, as well as precise resistors with a narrow tolerance range (±0.1%) and a low temperature coefficient (25 ppm/°C). The latter are designed for calibration circuits, operational amplifier tuning, and numerous devices that require a minimum margin of error due to the functions they fulfil (e.g. medical products, measuring instruments). Not that the majority of components come with the AEC-Q200 certification, which means that they can be used in motor vehicle electronic circuits (sensors, controllers, on-board system components, etc.).

THT resistors

The through-hole assembly (THT) resistors from Royal OHM include metal-film or carbon resistors. Their rating variants range from 120 mΩ to 10 MΩ (excluding the 0 Ω models). Some of them withstand voltages reaching even 3500 V (4000 V within a pulse). Similarly to the SMD resistors, the tolerance rating of the most precise products is ±0.1%, with an even lower temperature coefficient of 15 ppm/°C. The supplier’s product range is extensive and diverse to meet the needs of most electronics manufacturers – from consumer appliances (consumer electronics, white goods) to complex industrial systems.

Power resistors

Power resistors are a unique product group including both components used in electronics engineering (e.g. consumers or shunts in current measurement applications) and durable, high- voltage components used for high load control purposes. The latter include brake resistors used to dissipate energy generated during the motor braking process (which are used e.g. in elevator control systems). They operate at 1–1000 W, and their resistance rating ranges from 82 mΩ to 100 kΩ. This product range includes cement resistors featuring classic leads and most commonly installed directly on PCBs. Larger elements are enclosed (also with pre-installed heat sinks) or available in a modular form. Their terminals come in the form of axial, eyelet or cable connectors (255 mm). The Royal Ohm product range also includes high-voltage models designed as components that are resistant to pulses reaching even 8 kV.

Resistor networks

Royal OHM resistor networks come in two configurations: X-type (shared input pin for all the resistors in the network) and Y-type (one of the outputs connected between a pair of resistors). These are the typical types used for analogue signal processing, operational amplifier tuning, etc. The X-type resistor networks can also replace a number of individual resistors (e.g. current limiters for LEDs). The Royal OHM resistor networks are available both in SMD and THT versions. A single housing encloses from 3 to 9 resistors assuming values ranging from 10 Ω to 1 MΩ. For products intended for through-hole assembly, the package of leads is the standard 2.54 mm, while surface-mounted components come in 0804 and 1206 formats. The voltage rating of these components is up to 50 V or 100 V.

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