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High voltage application

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High voltage resistant resistors

Applications and required characteristics of high voltage resistors

High voltage resistant resistors are used in high voltage sensing, feedback, charge/discharge circuits, etc., which require high insulation performance.
Charge/discharge circuit High voltage sensing
  • High power rating
  • High overload resistance
  • Narrow resistance tolerance
  •  Low T.C.R.
  • High resistance value
  • Network resistors

Rated voltage and maximum working voltage of a resistor

Either the rated voltage or the maximum working voltage, whichever is lower, can be applied across the resistor. The resistance value at which the rated voltage and the maximum working voltage equal is called “critical resistance value".

Since rated voltage is determined from power rating and nominal resistance value, the rated voltage varies according to the power rating within the critical resistance value.

Allowable power

The higher the maximum operating voltage, the wider the resistance value range that can be used at the power rating.

Configuration of high voltage resistant resistors

Followings are components built on the insulator and substrate to constitute a high voltage resistant resistor.

 
  • Resistive element
  • nternal electrodes for connecting elements
  • Protective coat for protecting the element
  • External electrodes for soldering

High voltage resistant resistors for high voltage sensing and discharge circuits are designed to withstand higher voltages than ordinary resistors.

Resistive element pattern

A special kind of paste is used and a resistor pattern is formed using KOA's high printing technology according to dimensions and resistance values to withstand high voltage.

The following is an example of resistive patterns for chip type resistors.

Solid pattern Meander pattern Serpentine pattern

Common patterns for thick film resistors

This pattern is used for equal-length wiring of signal lines. Drawing a long line of it has an effect of reducing the voltage gradient of resistors.

 

Using this pattern, resistance value can be adjusted higher through trimming and gets even higher when used in resistor printing.

 

Resistance adjustment (trimming)

Resistive elements are formed and then trimmed for resistance value adjustment.

Common trimming methods include single-cut, double-cut, and L-cut, but KOA has applied these trimming methods and has established its own trimming method to withstand high voltages.

Single cut

Double cut

L cut

General trimming method

Voltage coefficient

Normally in resistance measurement, the resistance is measured with a very small current (= low voltage) in order to avoid resistance change due to self-heating, but when the applied voltage is changed, the resistance also changes even without the effect of TCR. The rate of change is called the voltage coefficient (ppm / V).

Generally, high-voltage resistors tend to have a better voltage coefficient than general resistors. When the potential difference across the resistor is large, consideration should be given to the voltage coefficient.
 

Creepage distance

In order to ensure insulation between circuits in electronic circuit boards, the regulations for creepage distances of conductors and insulators are set by IEC60664-1 and UL840. Since required creepage distances specified in above standards differ depending on applications, attention must be paid to secure the proper creepage distance for each application.

Lineup of high voltage resistant resistors

Shape Series Product Name
HV73 Flat Chip Resistors For High Voltage
HV73V Flat Chip Resistors For High Voltage (For Automotive)
HV73-RT Flat Chip Resistors For High Voltage (Anti Sulfuration)
HV73V-RT Flat Chip Resistors For High Voltage
(For Automotive, Anti Sulfuration)
RCR Coat-Insulated Fixed Anti Surge Resistors
GS High Voltage High Resistance Thick Film Resistors

Voltage dividers for high voltage sensing

When sensing a high voltage, generally, multiple resistors are mounted in series to divide the voltage, but by using a high-voltage divider with a high resistance ratio, the high voltage can be accurately sensed just with one package.

The resistance ratio of voltage dividers for high voltage detection gets less effect of temperature and less temporal changes since it is accurately adjusted, allowing elements to have uniform characteristics.

High voltage divider-precision type for high voltage sensing　HVD

Since two resistive elements are formed at the same time, the T.C.R. is relatively accurate, enabling high-precision voltage sensing even in environments with significant temperature changes. (Customizable)

Lineup of high voltage dividers

Item Series Product Name
SMD type HVD  Thin Film Network Resistors For High Voltage Divider