Introduction to ECO Standby and Shutdown Mode for TV Applications
Introduction
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Nowadays, as energy demand continues to rise, governments and power-saving agencies are paying more and more attention to power conversion energy efficiency and standby energy consumption. Since many devices are always powered but do not perform certain functions, a variety of voluntary and mandatory regulatory standards have been introduced worldwide. These new standards focus on reducing no-load standby energy consumption, with a minimum requirement of 0.3W. Due to the increasing energy burden of this no-load mode, major TV manufacturers are looking to further improve performance by limiting standby power consumption to less than 0.1W. Although this is not a mandatory performance requirement, it will help drive the adoption of the ECO standby model.
In addition to the ECO standby mode, a full shutdown mode can be used, which focuses on reducing energy consumption to below 25mW or even 0W. If the most traditional solution is to use the main power switch, we will see another option that is better at cost and safety metrics later.
In the end, TV manufacturers will be aware that green products can bring more market benefits, highlighting the difference in their products in the face of rising energy costs and environmentally conscious consumers.
Overview
The ECO standby power converter provides extremely low power consumption and also supports full standby, which can be turned on via remote control, infrared (IR) function and peripheral control (EU SCART specification). The converter should consume less than 8 mA (or less than 40 mW of energy) in standby mode to ensure that the total TV power consumption is less than 90 mW. This may require the use of a dedicated standby microprocessor (μP), which has become a more advanced technology for ECO standby mode.
Traditional fixed-frequency switching regulators offer excellent performance in terms of maximum output power, but they do not provide optimally low output power performance due to the use of a compression cycle to mitigate possible noise problems in the skip cycle mode. We used to like hysteresis mode switching regulators to reduce the number of switching cycles by light load and limiting switching losses.
Even though the main power switch is compatible with cathode ray tube (CRT) televisions in Europe and Asia, single flat panel TVs do not require components to comply with safety/standard specifications (voltages no higher than 4kV). Although not mandatory, we are seeing more and more flat-panel TVs starting with a main power switch to support the "green shutdown mode." Although this solution seems to be the easiest, in order to avoid the safety problems and the risk of fire (may require vanadium oxide (VO) casing plastic materials), high peak surge current and the required isolation around the switch (switches and cables and The mechanical isolation between the metal components of the TV casing makes the mechanical design both complicated and expensive. The position of the switch in the enclosure is also important, as the cable position may cause the EMI filter to become a "bypass" component, which may increase electromagnetic interference (EMI) issues.
Due to the excellent performance of the ECO standby solution under no-load conditions, we are able to provide a shutdown mode with a mains power consumption of less than 25mW. This shutdown mode is controlled by a small low voltage/low cost switch connected to the secondary side without adding any isolation and EMI issues. This solution meets the most stringent safety requirements, does not allow the TV switch to turn on (otherwise the switch is off), and does not consume more than 15W in any safety test.
　　
Figure 1 Circuit diagram of the primary side of the standby switching power supply
In order to be able to maintain such low power consumption in standby and shutdown modes, we use relays to disconnect the components that are not used in these modes. The relay is powered directly from the 5V standby power supply and is controlled by the TV microprocessor. In standby mode, parasitic energy consumption of approximately 100mW (PFC peripheral components and mains filter X2 capacitor discharge impedances) can be avoided.
The standby switching power supply should be powered by a dedicated diode that is directly connected to the mains input (in front of the relay). Since the power in the standby mode is limited, single-phase rectification is sufficient. The PFC output “takes over the power†by the PFC. The 400V voltage is used to supply the standby switching power supply. The 400V voltage is derived from the PFC in the operating mode. Provides up to 7.5W of power (1.5A current) at the 5V standby output.
　　
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Figure 2 provides the ON mode when the 400V PFC output voltage and maximum output current are provided.
Standby switching power supply primary side
The standby switching regulator IC100 is capable of starting up for a short period of time within the mains supply voltage due to the embedded start-up regulator (start-up time is less than 20ms at 90Vac). The IC operates in hysteresis mode, internally limiting the maximum constant primary current, providing regulation and adjusting the converted energy with a variable period. To provide very low output power consumption in standby mode, the controller operates at very low frequencies, maintaining the same maximum current per cycle, dramatically reducing switching losses, providing energy efficiency for low energy/ECO modes (at 90Vac) At voltage, the 71Hz skip cycle mode frequency at no load rises to 322Hz, providing an output of 8mA/40mW).
Standby switching power supply secondary side
The power supply is designed to provide a single 5V standby power supply with up to 1.5A in conduction mode. The TLV431 (shunt regulator IC101) is used for regulation, reducing the current consumption of the ECO mode (because polarization requires lower current) and providing greater voltage margin for the 5V supply.
Functional off switch
The switch can be much smaller than the total power switch, requiring only 10V and 2A DC. The switch is connected to the secondary side and does not need to be isolated from the metal parts of the TV case and there is no risk of fire at voltages below 10V.
The entire solution meets the safety requirements, does not allow the TV to switch to the on/operating mode if the switch is not operating, and ensures the energy consumption of the main power supply in any safety test (short circuit or open circuit of any electrical components) Less than 15W.
The standby power supply will remain active when there is no output load. When powered by 230Vac, the main power supply consumes less than 25mW. The solution achieves higher performance at a lower cost and avoids possible safety issues, providing an excellent alternative to the main power switch.
Figure 3 standby switch power supply secondary side circuit diagram
Standby/conduction control and overvoltage protection (OVP)
The "standby" control from the TV microprocessor will control the power supply, allowing the system to enter the on/operate mode or force it into standby mode. Since the "standby" controls voltages up to 5V, the signal transistor drive relay uses the main supply voltage to power the PFC while driving the optocoupler to power all of the primary controllers/ICs with the standby supply auxiliary voltage VCC1.
When the TV enters standby mode, both the relay and the optocoupler will be turned off by the standby control line.
Secondary 5V standby output shorted to ground
In the case of a short-to-ground output, the current in the IC will remain at the same peak, but due to the inability to complete the energy transfer, the system will operate in continuous conduction mode, the root mean square (RMS) current in the transformer, IC, and diode. It is much higher.
Since the regulation function is turned off, there is no feedback from the controller that drives the regulation pin. Since there is no feedback control, the IC will stop working until the Vcc voltage drops low enough to achieve a restart. The power supply will operate in a low frequency (about 7 kHz) boost or skip cycle mode with a 70% turn-off time to avoid any overtemperature or safety issues.
Overall energy consumption and energy efficiency performance
• When the mode is off/no load, the input power is lower than 25mW;
• When the 5V standby, the input power is lower than 90mW, and the output power is 40mW;
• When the input voltage is 90Vac, the current consumption of the 5V standby terminal in standby mode is up to 500mA;
• When the input voltage is 230Vac, the current consumption of the 5V standby terminal in standby mode is up to 1.5A;
• In conduction mode, current consumption is up to 1.5A with 400Vdc from PFC.
Figure 4 ECO standby power supply in the GreenPoint reference design of ON Semiconductor's latest TV power supply
in conclusion
For TV applications, it is now possible to use an ECO standby mode with less than 90mW of power consumption, full standby capability and compliance with all specifications. Although this mode requires a dedicated additional standby switching power supply, it features a high-power converter function without complex design, providing high standby mode performance (an additional switch that is critical to energy efficiency and safety). It is especially important that this solution can reduce energy consumption in an economical “off†mode due to its excellent “no-load†performance. It also helps to improve reliability and avoid the safety associated with traditional high-voltage main power switching solutions. risk.
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