Summary of low power control circuit and program design ideas

1: First understand the internal power consumption of the chip

When developing a handheld device, there is a key design issue that must be addressed. That is, how to achieve the lowest possible power consumption in standby mode. For example, if you use the Cortex-M0 core of Nuvoton Technology's NUC100 to develop a handheld radio,

1. The first thing to understand is the power consumption of the chip in deep sleep or sleep mode (that is, the operating current in this mode, note that general chips are at the uA level).

By checking the NUC100 chip data (which will be described in the electrical characteristics or DC electrical characteristics section of each chip manual), we can understand the maximum working current (i.e. maximum power consumption) and the minimum power consumption in deep sleep mode of the chip (the minimum power consumption is Ipwd1, Ipwd2, Ipwd3, and Ipwd4, which means that the internal modules of NUC100 require four external VDD interfaces to work. They should be added up when calculating the power consumption. Here is the minimum power consumption value of each VDD interface in sleep mode. Of course, if the chip can turn off the corresponding VDD of a module, it can reduce more unnecessary power consumption)

2. The first thing to understand is the power consumption of the chip in deep sleep or sleep mode (that is, the operating current in this mode, note that general chips are at the uA level).

By checking the NUC100 chip data (which will be described in the electrical characteristics or DC electrical characteristics section of each chip manual), we can understand the maximum working current (i.e. maximum power consumption) and the minimum power consumption in deep sleep mode of the chip (the minimum power consumption is Ipwd1, Ipwd2, Ipwd3, and Ipwd4. At first, we understood that it means that the internal modules of NUC100 need to provide four VDD interfaces externally. When calculating the power consumption, we need to add them up. Here is the minimum power consumption value in sleep mode of each VDD interface. Of course, if the chip can turn off the corresponding VDD of a module, it can reduce more unnecessary power consumption. In fact, it is not the case. Later, it was found that Ipwd1, Ipwd2, Ipwd3, and Ipwd4 represent the power consumption current measured in 4 cases, respectively. Later, the customer service of the chip manufacturer also confirmed that NUC100 can be below 25uA in deep sleep.)

2. Power consumption analysis of circuit power supply system

The following figure is the 7R handheld radio control circuit (using 2 ports for power on/off judgment processing, the waveform diagram when the button is turned on and off (the power on/off waveform is the same))

The working principle of the above diagram is as follows:

When POWER_KEY is not pressed, TP1 will remain at a high level (see the waveform of the next channel of the oscilloscope waveform below).

Since the voltage levels at both ends of C1 cannot change suddenly, both ends of C1 are high when POWER_KEY is pressed (in fact, C1 plays an accelerating role). In this way, the transistor Q1 will be turned on instantly due to the high level at the base, and then a low level will appear at point TP2. Then C1 will discharge through a loop formed by the base of Q1--Q1 emitter--R1--C1 (the waveform of the whole process is like the waveform of the upper channel in the oscilloscope screenshot below: a 2ms low level appears at the beginning, and then it discharges in an exponential form, Q1 is turned on, and then slowly cuts off, and finally the level of TP2 stabilizes at a high level). Note that the capacity of C2 is very small compared to C1, 0.1u=100000p. It is estimated that the role of C2 in this circuit is to filter out high-frequency components.

(It is easy to be confused here: C1 cannot mutate. When POWER_KEY is pressed, both ends of C1 cannot mutate. However, both ends of C2 cannot mutate. Therefore, both ends of C2 are at low level. Then the voltage at the intersection of C1 and C2 will be in conflict? Because the capacitance of C2 is very small compared with that of C1, it will hardly affect C1. Of course, if C1 and C2 are both 0.1uf, when POWER_KEY1 is turned on, since the voltage at both ends of C1 and C2 cannot mutate, their intersection voltage should be 2.5V)

(Capacitor-related understanding: [In-depth understanding of the working characteristics of capacitors])

The following is the power on/off function implemented by a port (because the INT0 and PB14 functions can be changed in the program):

The program control flow is slightly better with the addition of:

》》》

1: First understand the internal power consumption of the chip

When developing a handheld device, there is a key design issue that must be addressed. That is, how to achieve the lowest possible power consumption in standby mode. For example, if you use the Cortex-M0 core of Nuvoton Technology's NUC100 to develop a handheld radio,

1. The first thing to understand is the power consumption of the chip in deep sleep or sleep mode (that is, the operating current in this mode, note that general chips are at the uA level).

By checking the NUC100 chip data (which will be described in the electrical characteristics or DC electrical characteristics section of each chip manual), we can understand the maximum working current (i.e. maximum power consumption) and the minimum power consumption in deep sleep mode of the chip (the minimum power consumption is Ipwd1, Ipwd2, Ipwd3, and Ipwd4, which means that the internal modules of NUC100 require four external VDD interfaces to work. They should be added up when calculating the power consumption. Here is the minimum power consumption value of each VDD interface in sleep mode. Of course, if the chip can turn off the corresponding VDD of a module, it can reduce more unnecessary power consumption)

2. The first thing to understand is the power consumption of the chip in deep sleep or sleep mode (that is, the operating current in this mode, note that general chips are at the uA level).

By checking the NUC100 chip data (which will be described in the electrical characteristics or DC electrical characteristics section of each chip manual), we can understand the maximum working current (i.e. maximum power consumption) and the minimum power consumption in deep sleep mode of the chip (the minimum power consumption is Ipwd1, Ipwd2, Ipwd3, and Ipwd4. At first, we understood that it means that the internal modules of NUC100 need to provide four VDD interfaces externally. When calculating the power consumption, we need to add them up. Here is the minimum power consumption value in sleep mode of each VDD interface. Of course, if the chip can turn off the corresponding VDD of a module, it can reduce more unnecessary power consumption. In fact, it is not the case. Later, it was found that Ipwd1, Ipwd2, Ipwd3, and Ipwd4 represent the power consumption current measured in 4 cases, respectively. Later, the customer service of the chip manufacturer also confirmed that NUC100 can be below 25uA in deep sleep.)

2. Power consumption analysis of circuit power supply system

The following figure is the 7R handheld radio control circuit (using 2 ports for power on/off judgment processing, the waveform diagram when the button is turned on and off (the power on/off waveform is the same))

The working principle of the above diagram is as follows:

When POWER_KEY is not pressed, TP1 will remain at a high level (see the waveform of the next channel of the oscilloscope waveform below).

Since the voltage levels at both ends of C1 cannot change suddenly, both ends of C1 are high when POWER_KEY is pressed (in fact, C1 plays an accelerating role). In this way, the transistor Q1 will be turned on instantly due to the high level at the base, and then a low level will appear at point TP2. Then C1 will discharge through a loop formed by the base of Q1--Q1 emitter--R1--C1 (the waveform of the whole process is like the waveform of the upper channel in the oscilloscope screenshot below: a 2ms low level appears at the beginning, and then it discharges in an exponential form, Q1 is turned on, and then slowly cuts off, and finally the level of TP2 stabilizes at a high level). Note that the capacity of C2 is very small compared to C1, 0.1u=100000p. It is estimated that the role of C2 in this circuit is to filter out high-frequency components.

(It is easy to be confused here: C1 cannot mutate. When POWER_KEY is pressed, both ends of C1 cannot mutate. However, both ends of C2 cannot mutate. Therefore, both ends of C2 are at low level. Then the voltage at the intersection of C1 and C2 will be in conflict? Because the capacitance of C2 is very small compared with that of C1, it will hardly affect C1. Of course, if C1 and C2 are both 0.1uf, when POWER_KEY1 is turned on, since the voltage at both ends of C1 and C2 cannot mutate, their intersection voltage should be 2.5V)

(Capacitor-related understanding: [In-depth understanding of the working characteristics of capacitors])

The following is the power on/off function implemented by a port (because the INT0 and PB14 functions can be changed in the program):

The program control flow is slightly better with the addition of:

》》》

When extremely low power consumption is required in standby mode

Low power design problem: How to achieve a 0uA low power consumption of an MCU system in standby mode? (It cannot work in standby mode. How to turn on the system by long pressing the button and make the system work normally after releasing the button?)

analyze:

According to the system power consumption requirements, the MCU cannot work in standby mode. How can I turn on the system by long pressing the button, and make the system work normally after releasing the button? Then after turning on the system, long pressing the button again can enter the ultra-low power standby mode of 0uA.

solve:

When the system is in standby mode (shutdown), when the POWER_KEY1 button is long pressed, Q2 is turned on, and the high-level signal of the battery input voltage is directly supplied to the power supply end of the MCU chip. Then a GPIO port of the MCU immediately outputs a high level to keep the base of Q2 at a high level. The purpose is to lock Q2 to continue working, so that the MCU continues to be powered. In this way, even after the button is released, the system can be kept in working state.

When you need to shut down the system, press and hold the POWER_KEY1 button. This will detect the interrupt through the INT0 interrupt, and then the GPIO will no longer output a high level to latch the base of Q2. In this way, the system can be shut down when POWER_KEY1 is released. After shutting down the system, there is no power consumption.

Note: The figure below only provides an idea. This circuit needs to be improved. Is it safe to connect GPIO in this way? For example, Q2 can be replaced with a MOS tube, and the values ​​of each resistor should be selected according to the actual circuit, or resistors, capacitors and other devices can be added. Only then can this system work perfectly!

Three: Common ideas for designing low power consumption

How to use a multimeter to test the power consumption of a machine under stable voltage: switch the FLUK multimeter to the current range (note that the plug of the test lead should be switched to the current range), connect the red test lead to the positive pole of the power supply (there will be no danger if you use the black test lead), then connect the black test lead to the positive pole of the machine, and then connect the negative pole of the power supply to the ground terminal of the machine, and then you can measure the current.

Four: Common ideas for designing low power consumption

Reducing power consumption can not only greatly save electricity but also simplify the design of the power supply part. It can even be used on handheld devices. These are increasingly becoming the design direction of future products^_^

1 Reducing power consumption starts with MCU selection. When selecting, you should consider choosing a low-power MCU, such as MSP430, a CPU designed for low power consumption. 51 is strongly not recommended because it is slow. On the other hand, 51's IO has a pull-up resistor. Although the pull-up resistor does not consume power when the IO is high, it also consumes a lot of power when the pull-down current is generated. Another point is that the operation speed of 51 is too slow. Many operations using 51 require a very high main frequency, and a high main frequency means high power consumption.

2 Select the device power voltage. Obviously, lowering the device power voltage can significantly reduce the device power consumption. For example, although the internal structure of ATmega8 and ATmega88 chips is roughly the same, the latter can work at an ultra-low voltage of 1.8V while the former cannot. After comprehensive consideration, of course, the latter is chosen.

3. Try to reduce the operating frequency of the device. As we all know, the operating current of the CMOS circuit mainly comes from the charging and discharging of the capacitor at the input end of the next stage during the switch conversion. If the operating frequency of the MCU can be reduced, the power consumption will naturally decrease. You should know that the difference in operating current when the AVR works at 32.768Hz and when it works at 20Mhz is not small.

4 Try to use interrupts to put the processor into a deeper sleep. It is well known that sleep mode and power-down mode can greatly reduce the operating current of the MCU. Smart microcontroller designers can make full use of the interrupt function of the MCU to make the MCU work and sleep periodically, thereby greatly reducing the operating current of the MCU.

5. Try to turn off unused resources inside the MCU. This is a benefit that everyone on earth knows. I say this is a bit like nonsense. Why do you turn on things that are not used? For example, the analog comparator inside ATmega8 is turned on by default. Most of the resources inside ATmega88 can be turned off by software when not in use.

6 Try to use VMOS as an external power expansion device. The reason is simple. When VMOS is driven, it is a voltage-driven device that generates almost no power consumption, which is much more energy-saving than ordinary transistors. In addition, since the on-resistance of VMOS is low, usually only a few dozen milliohms, the device itself generates less heat when the current is small, especially when the current is small, the efficiency is much higher than that of traditional transistors. It is still recommended to use high-speed VMOS here, because high-speed VMOS will be more efficient when the switching speed is quite high PWM.

7 The power supply of external IC should be controlled by MCU's IO as far as possible. For example, the 24C02 we often use has power-off memory, so we can turn off the power supply when it is not working to save current. For example, the 6116 SRAM we often use, we can use the microcontroller to control its chip select port to control its operation and sleep to save current.

8 This is also the most vicious one. Usually when we drive some LED devices, we can completely control them through PWM and thus omit the current limiting resistor. We must know that when the device is selected, its internal resistance is also determined, and when the power supply voltage is also determined, the duty cycle can be used to determine the voltage on the device, thereby saving the current limiting resistor and also saving the power consumption of the current limiting resistor. If the user is using a battery, we can also detect the battery voltage from time to time and then change the duty cycle to keep the voltage on the load constant and achieve maximum utilization of the power supply.