Newsletter-Spring 2021
According to some research reports, there are many new electric vehicle (EV) models launched in the automobile market this year. Merely in the American market, the number of new EV models is already over 30. This shows the blooming development of EV in the market has been extended from commercial cars to passenger cars.
Coincidentally, MIH Alliance, which has just been established last year, has announced the first generation of EV Developing Tool-EVKit at the end of January. Through such an open platform, it has lowered the entry barrier for all EV and it is predicted to accelerate the popularization of EV. The MELF resistor is one of the key components of EV, so Firstohm has also joined MIH Alliance in the hope that the alliance members can better understand how the outstanding features of the MELF resistor can improve the quality of EV. By using MELF resistors, the designers can fulfil a long-term development trend of high reliability and stability.
New Releases of FIRSTOHM's Data Sheets
★ Data Sheets, special edition 2020
In response to the coronavirus pandemic around the world, Firstohm hopes to contribute more towards medical products. Our promise is symbolized through having the medical logo printed on the cover page. The hard copies of FIRSTOHM’s specification have been published in the end of 2020, please feel free to contact us if you need it.
★The soft-start resistors for Ebike application
In the motor start-up circuit, the voltage will generate mechanical stress on the motor and shaft in the moment during power ON. The Motors lifecycle will be greatly reduced due to this reason. Therefore, a soft-start resistor is added to the motor start-up circuit to reduce the direct impact.
Schematic
When SW1 is ON, the current (Ia) generates a voltage on the soft-start resistor to charge the capacitor. Once the capacitor is fully charged, the default setting up SW2 ON, and the current (Ib) is changed to the path without the soft-start resistor, then the motor will be operating on a full range of battery voltage.
Case study
The requirement of E-bike application is to withstand the maximum current of 0.25A per second for passing through SW1, resistance value at 82R, the maximum power consumptions are requested to be 5 watts for soft-start resistors.
Details of improvement
In the above case, it originally requires a high power (5W) in a very short period of time, thus two cement resistors (3W/PC) connected in series were used for the soft-start resistors. However, the disadvantage is that the used area of the circuit board is sacrificed, which is too wasteful for applications in a narrow space such as a bicycle and the cost is high.
According to characteristics of SRM101, Short Time Over Load: 2 seconds 2.5x rated voltage. Calculated power consumption of each resistor as below:
Rated voltage : V=√PxR =√(1W*82Ω)=9.055V, 2.5x rated voltage = 9.055Vx2.5=22.64V, P=V2/R= 22.642/82= 6.25W,Therefore, smaller FIRSTOHM SRM resistors (also a SMD-type component) are able to replace cement resistors, which in turn reduces the dimensions of the PCB.
soft-start circuit:
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