Solar energy products in electric tools, battery protection board, design, all kinds of power supply, current sampling is the lasting topic. Whether to do control, current general circuit adjustment, or over current protection, short circuit protection, the first step to consider the problem is to detect the current size.
There are two kinds of sampling methods currently used in more, one is the use of current transformer, the other is a current sampling resistor. The current transformer of good performance in some large current detection, but because of the expensive price, often for the amount is small, and the cost of not to what place requires. So all kinds of power supply, electric tools, battery protection board, lamps and lanterns, the drive motor or product supply part and other local mainstream is with high precision and efficient, economy, utility in second ways, is introduced in this paper the alloy resistance, as the current sampling.
With the resistance sampling, the general is the resistance is placed on the need to sample current position, to feedback by measuring the voltage across the resistor values, and to determine the size of the current in the circuit. Then the sampling resistor General requirements is relatively small, so as to make the resistance inside does not affect the size of primary current circuit, to ensure that the sampling precision. The main products of the resistance in the range of 0.0005 m ohm to 200m ohm, the resistance is small enough, according to the sampling voltage can choose the corresponding design requirements.
First look at the performance superiority of alloy resistance in use. Compared with the traditional ceramic chip resistors (such as thick film chip resistors, film chip resistors), alloy resistance of all aspects of major performance advantage, manifested in: tolerance better, temperature coefficient of TCR is lower, to + 50PPM/ DEG C, or even lower; higher power, the same rated power package case can transcend ceramic resistor several times. The most important point is the sampling and overcurrent protection for high current, short circuit protection which need by the impact of current place, the superiority of the prominent performance of the alloy resistance undoubtedly: Ceramic SMD resistor is often burned in a short time, and the alloy resistance can through the impact current considerable strength, so that in the whole circuit plays the protection of the other device function, while ensuring the overall quality of products.
Then compared with the alloy resistance wire resistance of the merits of some plug-ins. Comparing the same with metal wire resistance material, is the most intuitive alloy resistance advantages: stable product performance, high power, through the current, the material performance is stable and is not easy to oxidation, SMT automatically mount fast, high reliability, not because of subtle change of position welding and affect the access resistance (plug-in wire resistance welding the change of spot position slightly, can lead to changes of the resistance, is the sampling data out of the big error). Relevant information can refer to the following table:
It is well known that resistance when powered will emit heat, then the sampling of large current, resistance of power consumption is relatively large, the heating is also relatively high, this is the test alloy resistance performance is important one annulus. Both ends of the resistor are connected alloy pad position and the resistance of the body itself if the design is not reasonable, easy to appear in the high temperature end pole shift, even off the case. Alloy resistance with international patent "end copper electroforming", "end of silver plating" process to ensure product performance remains stable under high temperature, safe and reliable!