New functions are constantly being added to smart terminals, and battery life has become one of the most headaches for users. Compared with portable power supplies and cable power supplies, wireless charging technology has gained a lot of attention due to its convenience and versatility, making it one of the best solutions in the market. As one of the most popular applications in wireless charging technology, wireless devices need to provide better charging performance due to their long operating time.

C Wide impedance range is used to characterize inductance and quality factor
C High-precision DCR measurement
C Rapid measurement of manufacturing process
C A large number of fixtures to choose from

New functions are constantly being added to smart terminals, and battery life has become one of the most headaches for users. Compared with portable power supplies and cable power supplies, wireless charging technology has gained a lot of attention due to its convenience and versatility, making it one of the best solutions in the market. As one of the most popular applications in wireless charging technology, wireless devices need to provide better charging performance due to their long operating time.

This guide explains how the Keysight E4980A/AL precision LCR meter characterizes the most commonly used component in the wireless charging system—the coil.

Use the LCR meter to perfectly test the coils in the wireless charging system
Figure 1. E4980A precision LCR meter

Coil for wireless charging system

There is more than one wireless charging standard in use today, but they have a common feature, that is, coils (or coil-based resonators) are generally used to generate electromagnetic fields and transmit energy. A typical wireless charging system consists of two parts: a transmitting unit and a receiving unit. Power and energy transmission can be realized between the transmitter and the receiver through inductive coupling (Figure 2). Normally, the transmitting coil and driving circuit are installed on the charging stand, while the receiving coil and related circuits are built into the device that needs to be charged, such as a smart phone. Power transmission efficiency is a key indicator of wireless charging systems. This index is affected by many factors, such as the distance between the coils, parasitic inductance, and how the coils are arranged. For a single coil, in most cases, the lowest loss (low DCR) and parasitics (high Q) are required at the design stage. The typical test parameters of transmitter and receiver coils are Ls (series inductance), Rs (series resistance) and DCR (direct current resistance). The coil test frequency based on WPC standard is usually lower than 1MHz.

The E4980A/AL precision LCR meter is the industry standard solution for measuring components up to 2 MHz. This instrument is widely favored by the component manufacturing market due to its high accuracy and repeatable measurement, wide impedance range and high measurement speed.

Use the LCR meter to perfectly test the coils in the wireless charging system
Figure 2. Wireless charging system

High-precision standard DCR measurement

The DC resistance of the transmitter coil and the receiver coil will directly affect the resistance loss of energy transmission, so low DCR (usually as low as milliohms) is required to ensure high power transmission efficiency.

DCR (direct current resistance) measurement is a standard feature of the E4980A/AL precision LCR meter. E4980A/AL can measure DCR values ​​as low as milliohms very accurately. At the same time, E4980A/AL supports low contact resistance fixtures, such as 16047E and fixture compensation functions. If the DCR of the coil is 100 milliohms, the DCR accuracy of E4980A/AL can reach 5%, which means that the true value is between about 95 milliohms and 105 milliohms. This accuracy is very high, because the LCR meter based on the automatic balance bridge method is very difficult to measure low DCR.

Wide impedance range for measuring inductance and stable small ESR

The inductance of the transmitter and receiver coils is usually in the microhenry μH range, and the test is carried out in the frequency range of tens of kilohertz. Therefore, the impedance ranges from a few milliohms to a few ohms. The E4980A/AL LCR meter has excellent performance in a wide impedance range, and can maintain an accuracy of less than 10% between 4 milliohms and 100 milliohms (Figure 2), which is particularly suitable for the measurement of coils in wireless charging systems.

The equivalent series resistance (ESR) of the inductor also needs to be small and stable to meet the requirements of low power consumption. E4980A/AL provides excellent measurement stability for ESR measurement (Figure 3).

Use the LCR meter to perfectly test the coils in the wireless charging system
Frequency Hertz
Figure 2. 10% impedance measurement accuracy range (test signal 1Vrms, MED mode, cable 0m)

Use the LCR meter to perfectly test the coils in the wireless charging system
Figure 3. Low impedance evaluation (E4980A, 1 milliohm 100K Hz)

Fast measurement, improve product yield

The main concern of the manufacturing industry is to increase output and reduce test costs. E4980A/AL has a fast measurement function, which improves the measurement efficiency of design and manufacturing. The measurement speed of E4980A is as follows:

・Short (SHORT) mode, 1 MHz for 5.6 milliseconds per point
・In medium (MED) mode, 1 MHz is 88 milliseconds per point
・In LONG mode, 1 MHz is 220 milliseconds per point

A large number of test fixtures meet the test needs

The E4980A/AL LCR meter can be matched with more than twenty kinds of fixtures to meet various evaluation requirements from materials to SMD components. The 16047 series lead wire fixture is the best fixture for measuring low DCR and ESR lead wire coils. In addition, the built-in compensation function of E4980A/AL minimizes the impact of the test fixture.

The Links:   7MBR10SA120-70 RM500UZ-H