Principles for the selection of high power resistors

I. The following principles must be noted:

Metalized film resistor series will have reverse oxidation reaction under DC load, and this reaction will be more serious in hot and humid environment. When the resistor is subjected to AC load, if the operating frequency is low, the resistor can be wound according to

Wirewound resistors, metal oxide resistors, metal film resistors, carbon film resistors, synthetic film resistors and synthetic solid pistons resistor series are available.

When the operating frequency is above several tens of kHz, high frequency characteristics should be considered. In general, the drift of metal film resistor series film resistors is three times that of carbon film resistor series. Therefore, in power or amount applications

When the carbon film resistor series seems to be lower than the drift failure of the gold pressure film resistor series. There is a precision alloy foil resistor that combines the advantages of both metal film and wirewound resistors, with very stable resistance values and good probability characteristics.

And there are very good chance characteristics, when the operating frequency is below 5 MHz, it is basically a pure resistance, so it is often used as a standard electric gall.

1、Operating frequency

Resistors applied to the AC load, should consider the frequency characteristics. When the frequency increases, due to distributed capacitance, skin effect, dielectric loss resistor body and inductance effect caused by the lead, and other factors.

The resistance value will deviate significantly from the nominal value. The operating frequency of wirewound resistors is generally not higher than 50kHz, while the operating frequency of non-inductive wirewound resistors can be as high as 1MHz or more.

2、Resistance Value Stability

If the circuit function has higher requirements for the resistance value stability, such as the precision subtractor, sampling voltage divider circuit, etc., then attention should be paid to the selection of different load conditions according to the electric shaded device. When working thousand DC negative beauty, should be wound

Wire resistors, carbon film resistors, gold house film resistors, metal oxide film resistors, synthetic film resistors. The order of synthetic real-loaded resistors is preferred

Synthetic film resistors and synthetic solid drug resistor series rarely open-circuit, short-circuit failure, but the resistance value is not stable enough to have tolerance design of the insensitive circuit, the use of such resistors can prevent the resistor sudden

The use of these resistors can prevent equipment failure caused by sudden resistor failure. Therefore, these two types of resistors are often used in certain circuit designs with high reliability requirements.

3. Load Characteristics

The resistor value for AC and DC loads should not be greater than the power rating of PR. When the body of the electrical class is used in the ambient temperature Ta is greater than the allowable ambient temperature TR, the relationship between the use of power P and the nominal power is:

P=PR(Ta-TR)(Tmax-TR), that is, PR should be reduced to use. Under the pulse power, the resistor peak power may be several hundred times the average power, the main limiting factors are:

(1) High voltage causes interlayer breakdown;

(2) pulse current when the large exceeds the allowable current inductance. The order of the negative cutting ability of the electrical Ming off-load zero service is the wire line electric service, carbon fat electric service, metal-air plane electric service, metal and chemical illumination electric group device, synthetic into

resistors, high-voltage glass glaze resistors.

Resistor Selection Guidelines

According to the different materials used, resistors and potentiometers can be divided into three categories: alloy type, film type, and synthetic type, and other categories according to the structure and use. Depending on the use requirements, the preferred

The types of fixed resistors are also different.