标签: sleep

This is not a trick question. Your options for answers are as follows: Always Sometimes Maybe It depends As with most engineering issues, the correct answer is either c or d, based on your perspective, your priorities, and the specifics of the situation. It also is related to the basic definition of power and energy: Energy is the time integral of power. Many people, however, confuse "energy" and "power" both in concept and as physical entities.   I started thinking about this again after reading a brief Wall Street Journal piece, " Europe's Dirty Floor Mandate " (subscription required), and a related article in the Telegraph, " EU to ban high-energy hair dryers, smartphones and kettles ." According to the WSJ, "Consumers are only now noticing Regulation 666/2013, adopted by the European Commission last year and taking effect next month, which bans the manufacture or importing of vacuum motors whose power output exceeds 1,600 watts, with the limit dropping to 900 watts after Sept. 1, 2017."   The Telegraph reports that similar power-reduction plans are in place for appliances such as hair dryers. All of this, of course, is in the name of "saving energy."   Here's the problem: If you can accomplish the same task with a lower-power motor as compared with a higher-power motor and in the same time , you certainly will have saved energy. But if it takes longer due to the reduced power level, you may end up using the same or even more energy. In the case of reducing the motor power in a vacuum cleaner, the consumer may have to run it longer, so we are back to basics: Actual energy used is the time integral of power.   Perhaps it is possible to reduce a vacuum cleaner's power consumption significantly, while getting the same results, by using a more efficient motor and airflow arrangement. I don't know how efficient a vacuum cleaner really is or how much upside potential there may be. I do know that more efficient motors generally require more copper wire in their windings, so power consumption may be reduced for a given suction rating and airflow volume, but the total cradle-to-grave energy "expense" may actually be higher. It's hard to say.   (Side note: I never understood why vacuum cleaner "powerfullness" was discussed in terms of motor current draw -- amps. That always seemed to be looking at the wrong end of the story, and it assumed all motors and their vacuum cleaners had equal input current/output performance ratios.)   What really has me puzzled is the push toward greater electrical efficiency in appliances where the core function is to provide heat, such as hair dryers. A 1,000W dryer will surely take longer to dry hair than a 1,500W unit.   Aren't hair dryers and other electric-heat products 100% efficient by definition, except perhaps for some losses in their fan and an IR drop in their AC wires? I once measured a commodity 1,200W hair dryer's power consumption in no-heat/cold-air-only mode. I found that the very noisy fan took only about 50 W, an insignificant amount compared to the 1,200W full-heat rating. Even a somewhat better fan motor would not make much difference in overall energy use.   Have you seen other examples where people confuse energy with power and think that, by reducing one, they will automatically save on the other? Have you seen cases where reducing power consumption has actually increased energy use? It even happens with power-miser low-power systems that have a sleep mode. Sometimes it is more energy efficient to have a short, high-power activity burst and a longer sleep period, rather than a longer, medium-power burst and shorter sleep mode.

  STM32如何进入sleep模式 网上说STM32 STOP模式和Standby模式的不少，却很少有人说怎么操作Sleep模式，东西不多，加一个函数而已，废话不多，下面就给出添加的函数，各位COPY到自己的项目用就是了！！ /* *　　Brief　　:　　Enters SLEEP mode. */ #define PWR_SLEEPEntry_WFI         ((uint8_t)0x01) #define PWR_SLEEPEntry_WFE         ((uint8_t)0x02) #define SysCtrl_SLEEPONEXIT_Set    ((u16)0x0002) #define SysCtrl_SLEEPDEEP_Set  ((u16)0x0004) void PWR_EnterSLEEPMode(u32 SysCtrl_Set, u8 PWR_SLEEPEntry) {     if (SysCtrl_Set)          SCB-SCR |= SysCtrl_SLEEPONEXIT_Set;         else         SCB-SCR = ~SysCtrl_SLEEPONEXIT_Set;     SCB-SCR = ~SysCtrl_SLEEPDEEP_Set;         if(PWR_SLEEPEntry == PWR_SLEEPEntry_WFI)                    __WFI();                                             else         __WFE();                                 }