Getting standby power below 50mW

Article By : Akshat Jain, Ranajay Mallik

Here's a system developed with STMicroelectronics' VIPer0P device to help you cut standby power in a typical application to below 50mW.

« Previously: Standards on standby drain

Our deisgn uses the VIPer0P device, which in normal operation behaves as a standard flyback converter (figures 4 and 6). Both the main load and the auxiliary stage are fed from the main output. Upon a specific user command decoded by the microcontroller, the system enters the zero power mode.

In zero power mode, there is no switching activity. So no voltage is available at the output. The microcontroller remains ON and might also be used to switch OFF the main load in case of larger appliances.

The key blocks of the VIPer0P that remain alive are the "Zero-Power Logic" block and the 4V regulator (see figure 2). The 4V linear regulator supplied from Vcc provides those few micro Amperes needed to operate and keep the "Zero-Power Logic" block alive. Both pins ON and OFF are internally connected to this 4V supply line via 50kΩ pull-up resistors, so either of them can be used to provide a small current to some external circuit, like the microcontroller, as explained above.
The VIPer0P has low consumption and operates in pulse frequency modulation under light load.

[LowStandByPower Jain Mallik ST Figure3 cr]
Figure 3: VIPer0P can switch between modes as shown above.

A microcontroller powered up by ON and OFF pin of VIPer0P IC for smart zero-power mode management is shown in figures 4 and 6. VIPer0P supports flyback, buck and buck-boost converter designs. The microcontroller supervises the operation of the appliance and shuts down the SMPS by pulling low OFF pin and wakes it up by pulling low ON pin (figure 3 above).

The status of the pushbutton or tactile switch or capacitive touch is sensed by other GPIO pins of the microcontroller. As the microcontroller needs to be powered up during zero power mode, so it must be equipped with advanced features of power management, such as a low consumption standby mode with fast wake-up, as in the STM32L0xx series of microcontrollers.

[LowStandByPower Jain Mallik ST Figure4 cr]
Figure 4: Zero standby power architecture based on non-isolated flyback topology.

A 7W dual output (+7V and -5V) offline flyback converter for home appliances based on VIPer0P and STM32L052K6 microcontroller has been developed (see figure 5). The system is equipped with push buttons and capacitive touch-sense user interface to demonstrate the zero power mode of VIPer0P.

The standby power consumption we have measured with the evaluation board is:

  • less than 20mW (Input: 115V AC)
  • less than 50mW (Input: 230V AC)

[LowStandByPower Jain Mallik ST Figure5 cr]
Figure 5: An evaluation board based on the VIPer0P and STM32L052K6.

The non-isolated flyback topology configuration (figure 4) addresses the appliances that have a working cycle initiated by the user and autonomously terminated. However, there are various appliances that are switched on and off by the user via an RF or an IR remote control, such as air conditioners, TV sets, Hi-Fi systems and home cinema systems. These can also be addressed using the flyback topology shown in figure 6 below.

[LowStandByPower Jain Mallik ST Figure6 cr]
Figure 6: Zero standby power based on isolated flyback for RF or IR-remote controlled appliances.

Here we have shown that with added smartness to the VIPer0P, our target of zero standby power consumption, according to IEC62301 Clause 4.5, is within easy reach in most of the appliances. This smart saving energy reduces the consumer's electricity bill and helps achieve the larger goal of cutting emission of greenhouse gases.

By Akshat Jain, Ranajay Mallik
AMG Central Lab, STMicroelectronics India

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