The fuse resistor has the function of an ordinary resistor under normal circumstances. Once the circuit fails and its rated power exceeds its rated power, it will disconnect the circuit within a specified time, so as to protect other components. There are two types of fuse resistors: non-repairable and repairable.

Function

It plays the dual role of a fuse and a resistor in the circuit diagram, and is mainly used in the output circuit of the power supply circuit and the output circuit of the secondary power supply. They generally have low resistance (several ohms to tens of ohms) and low power (1/8~1W), and their function is to fuse in time when overcurrent occurs to protect other components in the circuit from damage.

When a short circuit fault occurs in the circuit load and an overcurrent occurs, the temperature of the fuse resistor will rise to 500~600°C in a very short period of time. At this time, the resistance layer will be peeled off and fused by heat, which plays the role of insurance and improves the The purpose of the whole machine safety.

Discrimination method

Although fuse resistors are widely used in power supply circuits, the marking methods in circuit diagrams vary from country to country and manufacturer. Although the label symbols are not yet unified, they have common characteristics:

(1) They are markedly different from the general resistor labels, which are easy to judge in the circuit diagram.

(2) It is generally used in low-voltage or high-voltage circuits with large current capacity of power supply circuits or secondary power supply.

(3) There is only one color ring on the fuse resistor. As shown in the attached picture, the color of the color circle indicates the resistance value.

(4) In the circuit, the fuse resistor is welded with long legs on the circuit board (generally, the resistor is welded close to the circuit board), and the distance from the circuit board is far away, which is easy to dissipate heat and distinguish.

Specifications

(1) RN1/4W, 10Ω fuse resistor, the color ring is black, and the power is 1/4W; when 8.5V DC voltage is applied to both ends of the fuse resistor, the resistance increases to more than 50 times the initial value within 60 seconds.

(2) RN1/4W, 2.2Ω fuse resistance, the color ring is red, and the power is 1/4W; when 3.5A current flows, the resistance increases to more than 50 times the initial value within 2 seconds.

(3) RN1/4W, 1Ω fuse resistance, the color ring is white, and the power is 1/4W; when the 2.8A AC current passes through, the resistance increases to more than 400 times the initial value within 10 seconds.

How to distinguish between ordinary resistors and fuse resistors

All have the function of resistance, but the resistance fuse is equal to the resistance plus the fuse. When the added power exceeds the power of the resistance, the fuse will blow, and the whole resistance will not burn and smoke. The resistance is when the added power exceeds its own power, it will burn up and smoke.

How to check the quality of the fuse resistor

Fuse resistors, also known as fuse resistors, are widely used in high-end electrical appliances such as televisions, video recorders, CDs, VCD players, instruments and meters. The fuse resistor plays a dual application of resistance and fuse in the circuit; under normal circumstances, it is used as a resistor; when the circuit fails (such as exceeding the specified load of the protected circuit), the fuse material on the fuse resistor body It will react with the resistance film layer (the reaction change time is calculated in seconds), causing the resistance film layer to break, making the resistance of the fuse resistor become very large or infinite, and protecting the relevant components in the related circuit from being damaged. The circuit symbol and package form of the fuse resistor, there is no unified regulation for the circuit symbol of the fuse resistor at present.

Testing method

1. The appearance is inspected by visual inspection under normal lighting conditions.

2. The external dimensions of the resistor are tested under normal lighting conditions with a vernier caliper with an accuracy of 0.02mm.

3. The electrical parameters are measured with the "YD2810D LCR digital bridge" tester at a frequency of 1KHz. For high temperature inspection, put the component under test into a 130°C electric heating constant temperature blast drying oven, and measure after 5 minutes.

4. For the electrical performance, use the "impact test bench (self-made, special for fuse resistance)" to continuously shock 30 times at room temperature, and then do the short-circuit fusing test.

5. The imprint on the surface of the resistor should still be clearly identifiable after wiping it with alcohol cotton for three times.

6. Pin bending resistance: Use tweezers to clamp the middle of any pin of the resistor, bend it 90°, and then straighten it. This is one time. It is required to bend 3 times in the same direction on the same plane. fracture occurs.

7. The weldability shall be inspected according to the weldability inspection specification, and shall meet the requirements of 5.2.1.

What should I do if the fuse resistance is damaged?

What should I do if the fuse is damaged? Once it is found that the fuse resistor is burned out, the original solid of the burning fuse resistor should be identified first, and it is never allowed to blindly replace it, let alone replace it with an ordinary resistor. If there is no fuse resistor of the same specification, emergency replacement can be carried out according to the following methods.

1. Substitute a resistor and a fuse in series Connect a resistor and a fuse (or fuse) in series to substitute, the resistance value, power of the resistor and the specification of the fuse resistor. For example, the specifications of the original fuse resistance are 10Ω and 2W, then the resistance can be 10Ω/2W. The rated current I of the fuse is calculated by the formula I squared R=56%P, where R is the resistance value (Ω), and P is the rated power (w) . This example results in a rated current of 0.3A.

2. Directly use the fuse instead of some fuses with smaller resistance value. After damage, you can directly use the fuse instead. This method is suitable for fuse resistors below 1Ω, and the fusing current value of the fuse can be calculated from the original fuse resistor according to the above formula.

3. The small electric bead used instead of the small electric bead has a certain resistance value. When the current increases to a certain value, the filament will glow or burn out. According to this feature, it can effectively replace the fuse resistor. The cold-state resistance of the commonly used flashlight beads is ten ohms to several tens of ohms, and the rated current is several hundred milliamps. The maintenance can be determined according to the actual situation.

Well, the above is the introduction of how to distinguish between ordinary resistors and fuse resistors. Have you learned it?