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greenpowerZONE Products for the week of July 7, 2008
STMicroelectronics Says…
Enhanced VIPer Family for Smaller, Lower-Cost and More Rugged Power Supplies
Avalanche-rugged 800-V MOSFET includes integrated protection, start-up and power-saving features that boost reliability, economy and efficiency
STMicroelectronics has introduced the VIPer17 off-line switched-mode converter, which integrates an 800V avalanche-rugged MOSFET as well as numerous features to save external components and ensure efficient operation during standby mode. Constant-current operation with an adjustable set point allows use with all mains voltages in SMPS (switched-mode power supply) designs up to 12W.
By integrating a high-voltage startup-current generator as well as essential protection functions, VIPer17 eliminates the need for external sensing components, as well as a startup resistor. Protection features include accurate, adjustable over-voltage and overload protection, hysteretic over-temperature protection, and two levels of over-current protection. Detection of a fault initiates the device’s auto-restart function, which prevents damage to the power supply or the load. An integrated soft-start function, active at startup or after a fault, reduces stress on the secondary diode and also helps prevent transformer saturation.
Under light-load conditions, such as when the powered equipment is placed in standby mode, the VIPer17 automatically enters burst mode to maximize efficiency. By achieving high efficiency at sub-1W loads, VIPer17 helps designers reduce system standby power and average power consumption to satisfy energy-saving initiatives such as Energy Star and Blue Angel. The device’s typical standby power consumption is 50mW, which can be reduced to 30mW when used in an optimized transformer design.
PWM operation with switching-frequency jittering also eases design challenges by reducing EMI at the switching frequency. This further extends the cost savings VIPer17 delivers in applications such as home appliances, consumer products and lighting systems, by reducing requirements for shielding.
The chip comes in a low-cost 7-pin through-hole DIP package (N type) and in a surface-mounting SMD package (D type). The physical layout of the device incorporates a double island for the power MOSFET and controller, to maximize reliability under a wide range of operating conditions.
EN-Genius Says…
The VIPer17 one-chip switch-mode power supply is actually a pair of co-packaged chips: a power MOS device nestled in next to a CMOS mixed-signal control circuit. Both chips are direct beneficiaries of STMicroelectronics' wise decision to keep most of its advanced analog and mixed-signal fabrication capabilities in-house. As we’ll see, keeping tight control of their analog and mixed-signal processes has allowed them to create some unique features that could give them a big advantage in the emerging green power market.
Like its distinguished competitors, this latest mains-powered switcher boasts efficient operation, low-power standby modes, and all manner of electrical protection which has become typical in the very mature generation of green PWM supplies that have hit the market over the last year or two. Despite all those similarities, STM has used its analog expertise and unique process capabilities to integrate the VIPer thermal protection circuitry directly into its power MOS section. Besides eliminating the cost of an external thermistor, an integrated thermal sensor provides a much quicker response than relying on the package thermal conductivity to pass on the news of an over-temperature situation to the appropriate shut-down pin. While they would not share many details of how they did it, the folks who briefed me said that integrating this one simple function took a small team of crack analog designers eight months to perfect.
Having control over their own process also played a big part in giving the VIPer17 its 800-V avalanche resistance, another unique feature that affords much better protection from big transients on its power inputs. While it’s a nice feature to have anywhere, the extra margin of protection may be a big selling point for products destined for less developed parts of Asia and other emerging markets where power is less reliable and subject to more spikes.
The result is a robust little supply with 80%+ efficiency that can function as a stand-alone supply for small items like set top boxes and cordless phones, or as an auxiliary supply in larger applications like big screen TVs, appliances, and high-powered gaming devices. When I suggested that it would make a great standby power supply for the new generation of 85 Plus-certified ATX computer power supplies, ST explained that this application actually needs to be capable of delivering around 20 W to run a full complement of USB ports and DC/DVD drives while the main CPU sleeps. Although this is well beyond the 12 W output of the VIPer17, ST assured me that they will be offering a variant targeted at 85 Plus ATX applications in the near future.
Given all the efficiency, protection, and other features crammed into the VIPer17, I’m surprised at the bargain-basement price that STMicro has placed on it. ST says that they have to offer it at a price that allows it to compete with simpler devices with comparable power ratings because the market still does not recognize the value of its green features. I’m hoping that the current energy crunch will change this a bit so that efficient devices will command at least a slight premium and innovators like STMicro can finally be rewarded for their pioneering efforts.
Available variants are the VIPER17LN / VIPER17LD or VIPER17HN / VIPER17HD with fixed switching frequency of 60 kHz or 115 kHz, respectively. The new devices join ST’s existing VIPER12 and VIPER22 converters, and are available immediately for production orders, at $0.37 in quantities of 10-k piece lots.
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