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CMOS Power Failure

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • The CMOS helps store hardware configuration settings in the Basic Input Output System (BIOS) and automatically updates the date and time even when the computer is shut down.

  • The CMOS power circuit is attached to the motherboard inside the computer. 

  • One of the reasons behind CMOS power failure is the low current of the CMOS drain, which ultimately discharges over time. 

CMOS Power Failure

The CMOS power circuit is attached to the motherboard inside the computer

Complementary metal oxide semiconductor (CMOS) power is the typical source in computer motherboards. The CMOS power stores hardware configuration settings in the Basic Input Output System (BIOS) and automatically updates the date and time even if the computer is off. CMOS power failure depends on the usage and environmental conditions of the computer. CMOS power failure affects BIOS settings, and, at times, the operating system is challenging to load.

Let’s discuss BIOS and CMOS power failure in this article. 

BIOS

In computers, BIOS is a read-only memory-based circuit. It is the BIOS that configures system capabilities. It contains low-level software that is required to enable communication with hardware.

The first and foremost function of BIOS is preparing the hardware for work, loading, and starting the operating system. Therefore, the first code to run when the computer is on is BIOS. The other functionalities of BIOS are to protect passwords, detect IDE drives, opt between processor or cache, etc. The BIOS needs to update the date and time of the computer, even when it is not in use. Power is essential for the BIOS to work correctly; the BIOS is powered with CMOS power. 

CMOS Power

With technological advancements, devices run on low power with a voltage rating of 3.3 V instead of 5V. The reduction in voltage levels decreases the footprint area and system costs. With reduced power, the reliability of the device can be enhanced. The reliability of BIOS is essential in computers, as it helps the operating system to load. The CMOS powers the BIOS and keeps it active whenever required.

CMOS technology powers the BIOS and keeps the settings in the computer up-to-date even when the system is unplugged. The settings include memory, date and time, hard drive configuration, booting sequence, etc. All these settings are configured to BIOS, powered by CMOS. 

The BIOS writes into CMOS memory, which is powered by CMOS technology. A CMOS power circuit is attached to the motherboard inside the computer. When the combination of PMOS and CMOS are used together in an electronic circuit, they are called complementary metal-oxide-semiconductors. The combination of positive MOSFETs (PMOS) and negative MOSFETs (NMOS) have characteristics such as low static power, higher noise immunity, etc. NMOS and PMOS are extensively used in electronic circuits due to the features mentioned above.  

CMOS Power Dissipation

Motherboard

CMOS power dissipation is essential to motherboard functions – failure can lead to a damaged motherboard

CMOS power is supplied by two MOSFETs - PMOS and NMOS combinations. The power is dissipated due to two statuses of the CMOS:

  1. CMOS is not switching 
  2. CMOS is switching

Depending on the operation condition of the gate of the CMOS, the CMOS power is dissipated statically or dynamically. 

Static Power

The power consumed when the CMOS is in static condition is called static power consumption. Static power is the power lost in the CMOS circuit due to the flow of leakage current through the transistors when the circuit is inactive or not operating.

Dynamic Power

The power consumed when the CMOS is in dynamic condition is called dynamic power consumption. Dynamic power is consumed by the CMOS circuit when it performs valuable work during the active mode of operation. Dynamic power consists of two components:

  • Switching power - The power consumed during the change in logic states of the CMOS circuit is called switching power.
  • Short-circuit power - The power consumed during the short-circuit condition of the CMOS circuit is called short-circuit power.

Total CMOS power = Static Power + Dynamic Power

CMOS Power Failure

One of the significant CMOS power failure reasons is the low current of the CMOS drain, which ultimately discharges entirely over time. The complete discharge of the drain current leads to CMOS power failure. In computers, CMOS power failure affects BIOS settings. CMOS power failure can result in some of the following conditions in a computer.

  1. The computer runs slow and shuts down in between.
  2. Difficulty in moving the mouse. 
  3. Trouble in loading the operating system.
  4. Date and time aren’t tracked.
  5. Damaged motherboard. 
  6. Intermittent problems.

The CMOS should be designed to prevent failure modes such as drain current discharge and significant power dissipation. Cadence OrCAD can help you design CMOS circuits and calculate power dissipation.

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