# Understanding low-power circuitry.

#### Eclipse19191919

Joined Sep 21, 2020
6
Hello,
(I have a very basic understanding of circuity)
How does a low power component, like a real time clock module, consume little power in a circuit?

This is my guess, but I do not know for sure. Lets say we have a 5V battery and a DS3234 real time clock module. Does its power consumption rely on its resistance? Aka the more resistance, the less current that flows through it?

Motors have huge current draw, yet they also have high resistance? Can someone explain how a module can be "Low power consumption"?

Thanks so much in advance.

#### dl324

Joined Mar 30, 2015
15,471
Welcome to AAC!

There's no generic answer for what low power means. There could be cases where someone's definition isn't low enough for a particular application.

Using resistance as a qualifier isn't appropriate. Some circuits save power by not powering circuitry that isn't being used. Others go into a low power mode when they're not doing anything.

Not all motors draw large currents.

You'll get more useful answers if you give specific situations.

#### sparky 1

Joined Nov 3, 2018
732
When someone says you have a voltage only circuit (ultra low current) it will not be a large motor. A motor gets hot and does work. Thermal properties and dipole gradients related to scale are difficult to visualize. So your guess resistance is correct in part for thermal. The geometry and fields that are involved in the silicon lattice at a smaller scale are more efficient. When you perform a level shift in a circuit there is no mystery that current and/or voltage has been scaled up or down. Now use the correct circuit vocabulary that explains how an electric circuit does this. Some electric micro motors are very small, the circuit must also be scaled down. The time clock watch tuning fork crystal requires very low current and the scale of the clock circuit can operate on very low current. When we consider the scale of the earth to the universe or the micro motor to large motor and what the circuit would be then you might understand that with good study habits you can take a transistor and some resistors to accomplish level shifting with the low current components or high current devices. I use a nano meter sometimes but femto meter takes a lot of skill. I recommend working in millivolts and volts first gaining experience and competency so that understanding the dynamics insides a time module includes the equipment in a semiconductor lab.

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#### MisterBill2

Joined Jan 23, 2018
13,809
"low power" in electronics usually refers to circuits that use active devices that require less power to function. This often also means that they use lower voltages. With the real-time clock module, it means that every component was selected for very low power requirements.
For a much more informative explanation go to a major semiconductor company website and read what they say about their low power devices.
Any discussions on youtube or similar venues will be useless bunk. And a google search will get thousands of hits wanting to sell you "low power" without any concept of what it means.

#### MrChips

Joined Oct 2, 2009
27,702
A real-time clock (RTC) is a digital circuit. In digital circuits, signals are either low or high, on or off. A digital circuit contains two FETs (field-effect transistor) wired in a totem-pole or push-pull configuration as shown:

The FETs are switches across the power rails. One switch is on while the other is off. The switches are never both on at the same time. If they were on, that would be a short circuit across the power rails and at least one of the transistors would likely blow.

Since one switch is always off, theoretically the circuit draws zero current. This is the basis of low power digital circuitry. While in operation, logic gates are being switched low and high, on and off. In order for the logic voltages to switch from off to on and back to off again, charge has to be added and removed from the gate inputs and outputs. This is where current flows. The amount of current depends on the inherent capacitance of the circuits and how often the signal has to change, i.e. clocking frequency.

The current consumption is directly related to the clock frequency, the higher operating frequency the more power is consumed. In low power circuitry, the goal is to lower the clock frequency. Where it is possible, stopping all clocks achieves the lowest power consumption. When all clocks are stopped the power consumed is primarily leakage current which can be of the order of nA, i.e. 1/1000 of 1μA.

An RTC circuit uses a 32.768kHz crystal oscillator running continuously in order to keep accurate time. Meanwhile an MCU which could be running at 20MHz at full speed would consume much more power. In order to reduce power consumption the MCU is placed into SLEEP mode or STOP mode when no processing is required.

A motor, on the other hand, is an analog device that draws higher currents while running.

#### MisterBill2

Joined Jan 23, 2018
13,809
A real-time clock (RTC) is a digital circuit. In digital circuits, signals are either low or high, on or off. A digital circuit contains two FETs (field-effect transistor) wired in a totem-pole or push-pull configuration as shown:

View attachment 217663

The FETs are switches across the power rails. One switch is on while the other is off. The switches are never both on at the same time. If they were on, that would be a short circuit across the power rails and at least one of the transistors would likely blow.

Since one switch is always off, theoretically the circuit draws zero current. This is the basis of low power digital circuitry. While in operation, logic gates are being switched low and high, on and off. In order for the logic voltages to switch from off to on and back to off again, charge has to be added and removed from the gate inputs and outputs. This is where current flows. The amount of current depends on the inherent capacitance of the circuits and how often the signal has to change, i.e. clocking frequency.

The current consumption is directly related to the clock frequency, the higher operating frequency the more power is consumed. In low power circuitry, the goal is to lower the clock frequency. Where it is possible, stopping all clocks achieves the lowest power consumption. When all clocks are stopped the power consumed is primarily leakage current which can be of the order of nA, i.e. 1/1000 of 1μA.

An RTC circuit uses a 32.768kHz crystal oscillator running continuously in order to keep accurate time. Meanwhile an MCU which could be running at 20MHz at full speed would consume much more power. In order to reduce power consumption the MCU is placed into SLEEP mode or STOP mode when no processing is required.

A motor, on the other hand, is an analog device that draws higher currents while running.

#### KeithWalker

Joined Jul 10, 2017
2,622
You mentioned the power used by motors. The windings on a motor armature have relatively low resistance. When it is running, the motor draws much less current than you would expect if you apply Ohm's law, except when it is stalled. Why is that? You need to do some basic research yourself so that you can understand the higher level answers that we will give you. Here is a good source of information for you to learn the basics:

https://www.electricaleasy.com/2014... 1,classification of DC machines here. More

Regards,
Keith

#### MisterBill2

Joined Jan 23, 2018
13,809
To reduce power consumption in CMOS systems the designs have greatly reduced the junction capacitance and the voltage that it is charged to. IN addition a lot of effort has gone into reducing leakage currents. So the low power devices really do consume less power, sometimes much less. The trade-off is both less output power and greater noise sensitivity. And sometimes there are major changes in the whole design which are kept secret so that the competition will not copy them.
Thus low power is not really a resistance function, except for increasing leakage resistances where there is leakage current.

A discussion of motors is an entirely separate thing, and it is not part of this discussion. Motor power is a function of both motor output and motor efficiency.

Joined Jul 18, 2013
26,304
Motors have huge current draw, yet they also have high resistance? Can someone explain how a module can be "Low power consumption"?
To what type of motor in particular are you referring to?
As the general rule does not comply with that statement.
Max.

#### MisterBill2

Joined Jan 23, 2018
13,809
I have an electromechanical clock that will run for over a year on a single AA cell, That is a low powered motor. I have a fair sized air compressor with a 230 volt motor that draws 17 amps. That is NOT a low power motor. Motor resistance is not the driver for determining motor power Motors and integrated cercuits are quite different.

#### SamR

Joined Mar 19, 2019
4,492
Since the inception of semiconductors, there has been a continuous push to reduce power consumption. Early transistor circuits were 9V. Later IC circuits were 5V and many now 3.3V or less. With the reduction of voltage and therefore power more "miniaturization" more circuitry could be integrated into chips. Many years ago a problem arose with trace size inside chips when a phenomenon of electron tunneling was observed. Trace size was so small the electrons were "straying" out of the trace into the substrate. To reduce tunneling, voltages of chips were reduced from 5V to 3.3V. That is the conundrum facing electronics. How low of a Voltage can we actually go? There is a wide variety of semiconductor components available today in a variety of voltages from legacy components to ultra power conserving ones. Read the PDF.

#### MisterBill2

Joined Jan 23, 2018
13,809
Low power operation involves more than just lowering voltages. Reducing the charge needed to change state and reducing leakage are also very big contributors to power reduction. Consider the low voltage operation of many CPUs in PCs, 3.3 volts and 20 amps.Now look at some of the low power IC devices, 3.3 volts and 14 MICROamps! . Certainly there is a whole lot of other change t get to low power.

#### Eclipse19191919

Joined Sep 21, 2020
6
Welcome to AAC!

There's no generic answer for what low power means. There could be cases where someone's definition isn't low enough for a particular application.

Using resistance as a qualifier isn't appropriate. Some circuits save power by not powering circuitry that isn't being used. Others go into a low power mode when they're not doing anything.

Not all motors draw large currents.

You'll get more useful answers if you give specific situations.
Here is an example: A 5 volt battery powers a 5v motor. Then a different 5 volt battery powers an LED+resistor. And finally another 5 volt battery powers a microcontroller.

Clearly the Motor drains the battery the fastest, then the LED and res, and then the microcontroller. Why does the microcontroller barely consume any energy compared to the other two. A very simple, over generalized answer will do.

Thanks!

#### Eclipse19191919

Joined Sep 21, 2020
6
When someone says you have a voltage only circuit (ultra low current) it will not be a large motor. A motor gets hot and does work. Thermal properties and dipole gradients related to scale are difficult to visualize. So your guess resistance is correct in part for thermal. The geometry and fields that are involved in the silicon lattice at a smaller scale are more efficient. When you perform a level shift in a circuit there is no mystery that current and/or voltage has been scaled up or down. Now use the correct circuit vocabulary that explains how an electric circuit does this. Some electric micro motors are very small, the circuit must also be scaled down. The time clock watch tuning fork crystal requires very low current and the scale of the clock circuit can operate on very low current. When we consider the scale of the earth to the universe or the micro motor to large motor and what the circuit would be then you might understand that with good study habits you can take a transistor and some resistors to accomplish level shifting with the low current components or high current devices. I use a nano meter sometimes but femto meter takes a lot of skill. I recommend working in millivolts and volts first gaining experience and competency so that understanding the dynamics insides a time module includes the equipment in a semiconductor lab.
How does one create/use a voltage only circuit?

#### Eclipse19191919

Joined Sep 21, 2020
6
"low power" in electronics usually refers to circuits that use active devices that require less power to function. This often also means that they use lower voltages. With the real-time clock module, it means that every component was selected for very low power requirements.
For a much more informative explanation go to a major semiconductor company website and read what they say about their low power devices.
Any discussions on youtube or similar venues will be useless bunk. And a google search will get thousands of hits wanting to sell you "low power" without any concept of what it means.
That's exactly the issue I have run into, it's a hard to question to simply google sadly.

#### dl324

Joined Mar 30, 2015
15,471
Why does the microcontroller barely consume any energy compared to the other two. A very simple, over generalized answer will do.
The power consumed by a microcontroller will be a function of supply voltage, transistor leakage current, the number of transistors switching, and the frequency that they're switching.

#### Eclipse19191919

Joined Sep 21, 2020
6
A real-time clock (RTC) is a digital circuit. In digital circuits, signals are either low or high, on or off. A digital circuit contains two FETs (field-effect transistor) wired in a totem-pole or push-pull configuration as shown:

View attachment 217663

The FETs are switches across the power rails. One switch is on while the other is off. The switches are never both on at the same time. If they were on, that would be a short circuit across the power rails and at least one of the transistors would likely blow.

Since one switch is always off, theoretically the circuit draws zero current. This is the basis of low power digital circuitry. While in operation, logic gates are being switched low and high, on and off. In order for the logic voltages to switch from off to on and back to off again, charge has to be added and removed from the gate inputs and outputs. This is where current flows. The amount of current depends on the inherent capacitance of the circuits and how often the signal has to change, i.e. clocking frequency.

The current consumption is directly related to the clock frequency, the higher operating frequency the more power is consumed. In low power circuitry, the goal is to lower the clock frequency. Where it is possible, stopping all clocks achieves the lowest power consumption. When all clocks are stopped the power consumed is primarily leakage current which can be of the order of nA, i.e. 1/1000 of 1μA.

An RTC circuit uses a 32.768kHz crystal oscillator running continuously in order to keep accurate time. Meanwhile an MCU which could be running at 20MHz at full speed would consume much more power. In order to reduce power consumption the MCU is placed into SLEEP mode or STOP mode when no processing is required.

A motor, on the other hand, is an analog device that draws higher currents while running.
Ah I think I am almost seeing the bigger picture here. Through some clever circuitry, there is never a direct path from Vcc to ground.

Here is my conclusion from reading your answer and somewhat understanding. Through the use of these types of circuits, charge is used to switch FETs constantly back and forth, never allowing a steady flow of current. Rather the charge used to switch the FETs is used is pulled from the battery in a sort of super fast way, where only enough charge to switch a gate is used?

I see now it is hard to explain in just simple terms like I initially hoped. I'm not willing to go much deeper into this topic, but I'm glad I now have more of an appreciation/awareness of what is going on in these circuits.
Thanks!

#### Eclipse19191919

Joined Sep 21, 2020
6
The power consumed by a microcontroller will be a function of supply voltage, transistor leakage current, the number of transistors switching, and the frequency that they're switching.
Ah cool, That's a really nice way to put it! Thank you

#### SamR

Joined Mar 19, 2019
4,492
Why does the microcontroller barely consume any energy compared to the other two
Once again, read the PDF. You may find a Quiescent (idle) Current and maybe even that the chip will go into a "sleep mode" of even less than the quiescent current if idle after a certain length of time. Active current may depend on the chip's activity. The current consumed also depends on supply voltage as many chips have a range of voltages that they operate within. You will also find Wattage limits and operating temperature limits and derating for temp. No simple answer as all chips are different.

#### MisterBill2

Joined Jan 23, 2018
13,809
In addition to the reasons already given for why some active devices use less power, some are designed to use less power. Less capacitance to charge as the gates change state is achieved by making things smaller. Go to the manufacturers site and see what they brag about as their way of reducing power consumption. It is a whole lot more than just reducing voltages.