Part 5 ― Power Devices for Motor Drive Applications

Newest Power Devices Enable Motor Control Solutions to Reliably Drive Electric Motors Ranging in Size from Small to Large

To provide total solutions for electric motor applications, Renesas complements its motor control microcomputers with power devices suitable for driving small to large electric motors. Our device portfolio includes power MOSFETs, thyristors, triacs, and other motor drive semiconductors. The MOSFET product line consists of power devices with voltage ratings between 12V and 150V for use in small motor drives. Key members of our thyristor and triac product lines are devices with withstand ratings up to 1000V that have a guaranteed junction operating temperature of 150°C.

In addition to a vast line of motor control microcomputers, Renesas supplies low-voltage power MOSFETs with ratings between 12V and 150V for use in small motor drives. Applications for these components extend beyond motor control, of course, and the general requirements for most situations are small package size and low on-resistance. For example, small packages are required to satisfy surface mount technology (SMT) requirements. The current design trend is to use SOP-8 or smaller sizes for devices with withstand voltages of 100V or less.

Renesas power MOSFETs in SOP-8 packages for small motor applications include single types (N-channel and P-channel) and dual types (Nch + Nch, Pch + Pch, or Nch + Pch). One product in a 4-in-1 SOP-8 package integrates four MOSFETs. The devices are also offered in DPAK, WPAK, LFPAK, LFPAK-i, and QFN56 packages, among others. For instance, a model that combines two MOSFETs in a single CMFPAK-6 package is ideal for use with ultra-small brushless motors.

For driving small three-phase brushless DC motors in automotive systems, we offer products that combine six MOSFETs in one package (see Figure 1). The package is a surface-mount type that uses a thick header frame to achieve a thermal resistance equivalent to an LDPAK. This package reduces the mounting footprint by 40 percent compared with six conventional single-MOSFET DPAK packages.

MOSFETs must have a low on-resistance to ensure low losses. Motor drives commonly operate at around 20kHz, a lower operating frequency than, for example, switching power supplies. Even inverters operate at around 15kHz, so a low on-resistance is necessary to keep losses low.

To reduce the on-resistance of our power MOSFETs, which have ratings from 12V to 120V, we use miniaturization techniques and have developed methods that optimize the internal structure of the silicon. The Renesas fabrication technology achieves a low on-resistance while maintaining the withstand voltage (Vdss), despite the fact that a MOSFET's withstand voltage is inversely related to the on-resistance. By reducing heat losses, a low on-resistance allows the use of smaller packages. Efficiency is gained while space is saved ― a "win-win" result.

Another characteristic of our power MOSFETs is that the devices have low drive power. This eliminates the need for an intermediate pre-driver circuit between the microcomputer and power MOSFET, saving additional space and reducing cost.

Renesas supplies thyristors and triacs for motor drives that require a high withstand voltage, such as whiteware or office equipment that operates on the mains AC power supply. Our extensive product range encompasses models with 600V, 700V, 800V, and 1000V withstand ratings that provide a guaranteed junction operating temperature of 150°C (see Figure 2). These devices use a planar structure that has a lower off-current than a mesa-glass structure. Their wide thermal design margin improves reliability and makes them easier to apply. The product range also includes models in which the cooling fan has been made smaller or eliminated altogether.

Products in the 600V to 1000V "LA" series are ideal for general use. Devices in the "LB" series (600V withstand voltage), which is based on the LA series, have a higher guaranteed junction operating temperature. The "LG" series can withstand higher voltages (600V to 800V withstand voltage), and the "LC" and "LD" series (600V to 700V withstand voltage) products are optimized for low in-rush currents.

Renesas intends to expand its range of power MOSFETs, thyristors and triacs to exploit the synergies that arise from their use with motor control solutions based on our microcomputers. Among the products currently under development are high-withstand-voltage/high-capacity triacs (1000V or 1500V withstand voltage) for high-voltage motor drives.