1. Some theory
1.1. Introduction
Almost every laptop has a charging circuit of some sort, that does a few things:
There are 2 different designs to handle switching between AC adapter and battery power and feeding the system:
Texas instrument has a nice overview of these technologies with some more details at https://e2e.ti.com/blogs_/archives/b...ing-topologies . The essential information is summarized below.
There are also 2 different designs to handle battery charging rail generation:
Almost all laptops without USB-C charging capabilities use a buck converter. Most of these use HPB, except Apple laptops which always use NVDC. A bunch of non-Apple ultrabooks use NVDC as well.
Almost all laptops (incl. Apple) with USB-C charging capabilities use NVDC with a buck-boost converter.
Some netbooks or entry-level laptops (especially ARM platforms and some Atom platforms) can have a circuit different to what is presented here, using a PMIC that handles almost every power-related features. Since these aren't common and highly depend on the board and the ICs used, they are not covered here.
For MacBooks without USB-C you have some more details on the charger IC here: https://logi.wiki/index.php/ISL6258_...roubleshooting
1.2. Hybrid power boost design
From https://en-support.renesas.com/knowledgeBase/13886169
In this design, the system is fed from the AC adapter, and a MOSFET (we will call it battery-to-system MOSFET) allows the current to flow from the battery to the system when on battery only, while prevent current from flowing directly from the AC adapter to the battery when AC adapter is plugged in.
Therefore, when on AC adapter, the main power rail voltage will be the voltage provided by the AC adapter. In general this voltage is between 19V and 20V. A few machines use 12V or 16V.
When on battery, the main power rail voltage will be the voltage provided by the battery. This depends on the number of cells in series in the battery and the state of charge, but it is lower than 19V. (see Battery voltage section)
Warning: Hybrid power boost provides an additional feature where the battery can provide additional power to the system even when running on AC adapter. Older designs used the same circuit but the charger IC was not able to provide this feature. The presence or abscence of this feature is irrelevant to this article, so the older designs will fall under the hybrid power boost term as well.
1.3. Narrow VDC design
https://en-support.renesas.com/knowledgeBase/6680047
In this design, the system is fed directly from the battery charging rail. The voltage on the main power rail is always close to the voltage on the battery. (see Battery voltage section)
1.4. Buck converter
This works the same as any single-phase synchronous buck converter. There's one high-side MOSFET and one low-side MOSFET turning on and off alternatively to step down the voltage from the input, for example from 19V to 12.6V.
(from bq24715 datasheet)
1.5. Buck-Boost converter
A synchronous 4-switch buck-boost converter uses a first set of high-side and low-side MOSFETs before the inductor. They can act as a regular buck converter to step down the voltage coming from the AC adapter. There's a second set of MOSFETs after the inductor, they are used as a boost converter to step up the voltage coming from the AC adapter.
That way, the machine can take 5V to 20V from an USB-C charger and still be able to charge the battery. Of course, with only 5V as the input, the power will be lower than with 20V, so the battery will charge slower and the laptop may not turn on without battery or when the battery is discharged.
(From ISL9238 datasheet)
1.6. Battery voltage
Laptops battery packs are based around lithium cells.
These are either Li-ion cells, round cylinder similar to your alkaline battery but in a 18650 package, or LiPo cells, flat rectangular cell like in a smartphone.
Li-ion cells typically have a nominal voltage of 3.6V to 3.7V, LiPo cells typically have a nominal voltage of 3.7V to 3.85V. It varies depending on the brand and series of the cell.
The battery voltage and by extension the voltage used to charge the battery depends directly on how many cells there are in series inside the battery pack.
Battery packs can be described with a "xSyP" number, where y is the number of cells in a group connected in parallel, and x is the number of groups connected in series.
All cells in parallel in a group will have the same voltage across them. Putting groups in series will sum their voltages.
For example a 3S2P pack with 11.1V nominal voltage contains 6 cells, 3 groups in series of 2 cells in parallel, for a total voltage across the pack of 3x3.7V = 11.1V.
The number of cells put in parallel in a group helps increasing the capacity, but it doesn't change the voltage. We are interested in the voltage here, so we will ignore the cells in parallel.
The "nominal voltage" represents the voltage around which the cell is throughout most of its discharge, it should be what you are able to measure on the pack when it's charged to around 50%.
When charged fully, the voltage will be higher, when completely discharged, the voltage will be lower.
Charging voltage will be a bit higher than the fully charged voltage of the pack. For example, an 11.55V pack (3S of 3.85V nominal) can in general be charged at 13.1V (4.35V per cell). An 11.1V pack (3S of 3.7V nominal) can in general be charged at 12.6V (4.2V per cell). A 10.8V pack (3S of 3.6V nominal) can in general be charged at 12.3V (4.1V per cell).
This of course highly depends on the exact type of cells used, and using a voltage that's too high for a given cell type can at best damage the cell, at worst be a safety threat.
1.1. Introduction
Almost every laptop has a charging circuit of some sort, that does a few things:
- Manages switching between AC adapter and battery power
- Manages battery charging and generates power rail to charge battery
There are 2 different designs to handle switching between AC adapter and battery power and feeding the system:
- Hybrid power boost (HPB) and traditional circuits without power boost (see Warning in HPB section)
- Narrow VDC (NVDC)
Texas instrument has a nice overview of these technologies with some more details at https://e2e.ti.com/blogs_/archives/b...ing-topologies . The essential information is summarized below.
There are also 2 different designs to handle battery charging rail generation:
- Buck converter
- Buck-Boost converter
Almost all laptops without USB-C charging capabilities use a buck converter. Most of these use HPB, except Apple laptops which always use NVDC. A bunch of non-Apple ultrabooks use NVDC as well.
Almost all laptops (incl. Apple) with USB-C charging capabilities use NVDC with a buck-boost converter.
Some netbooks or entry-level laptops (especially ARM platforms and some Atom platforms) can have a circuit different to what is presented here, using a PMIC that handles almost every power-related features. Since these aren't common and highly depend on the board and the ICs used, they are not covered here.
For MacBooks without USB-C you have some more details on the charger IC here: https://logi.wiki/index.php/ISL6258_...roubleshooting
1.2. Hybrid power boost design
From https://en-support.renesas.com/knowledgeBase/13886169
Originally posted by Renesas
In a Hybrid Power Boost configuration, the synchronous buck converter runs as a normal buck converter when the adapter provides power to the system and is charging the battery. When the adapter power is not sufficient, the synchronous buck converter runs in reverse to boost the battery voltage to around 20V. Thus the battery supplements the adapter whenever the adapter power is not sufficient. This requires no circuit changes from a traditional adapter.
The change is required in the control circuit (the battery charger controller). The advantage of this system over a traditional charger is that the battery is able to assist the adapter during turbo workloads. This system has the disadvantage that the light load efficiency is pretty low as it is difficult to achieve high light load efficiency at high input voltage.
The change is required in the control circuit (the battery charger controller). The advantage of this system over a traditional charger is that the battery is able to assist the adapter during turbo workloads. This system has the disadvantage that the light load efficiency is pretty low as it is difficult to achieve high light load efficiency at high input voltage.
Therefore, when on AC adapter, the main power rail voltage will be the voltage provided by the AC adapter. In general this voltage is between 19V and 20V. A few machines use 12V or 16V.
When on battery, the main power rail voltage will be the voltage provided by the battery. This depends on the number of cells in series in the battery and the state of charge, but it is lower than 19V. (see Battery voltage section)
Warning: Hybrid power boost provides an additional feature where the battery can provide additional power to the system even when running on AC adapter. Older designs used the same circuit but the charger IC was not able to provide this feature. The presence or abscence of this feature is irrelevant to this article, so the older designs will fall under the hybrid power boost term as well.
1.3. Narrow VDC design
https://en-support.renesas.com/knowledgeBase/6680047
Originally posted by Renesas
This figure shows the Narrow VDC (NVDC) topology. Here, the system bus (Vsys) is not connected directly to the adapter. It is connected to the output of the buck converter. Hence, NVDC operates only as a buck converter, both when NVDC charges the battery and when the battery supplements the adapter and provides power to the system. NVDC implementation reduces the switch-over period between the charging mode and the hybrid power mode. NVDC implementation allows the system to minimize the period of overloading the input power source when CPU is in Turbo Boost mode.
The advantage of using the NVDC system is that the overall system efficiency is better compared to the Hybrid Power Boost (HPB) charger. The system can be designed for a smaller voltage rating since the system has a lower Vin. The disadvantage is that the charger components’ size and power dissipation increases.
The advantage of using the NVDC system is that the overall system efficiency is better compared to the Hybrid Power Boost (HPB) charger. The system can be designed for a smaller voltage rating since the system has a lower Vin. The disadvantage is that the charger components’ size and power dissipation increases.
1.4. Buck converter
This works the same as any single-phase synchronous buck converter. There's one high-side MOSFET and one low-side MOSFET turning on and off alternatively to step down the voltage from the input, for example from 19V to 12.6V.
(from bq24715 datasheet)
1.5. Buck-Boost converter
A synchronous 4-switch buck-boost converter uses a first set of high-side and low-side MOSFETs before the inductor. They can act as a regular buck converter to step down the voltage coming from the AC adapter. There's a second set of MOSFETs after the inductor, they are used as a boost converter to step up the voltage coming from the AC adapter.
That way, the machine can take 5V to 20V from an USB-C charger and still be able to charge the battery. Of course, with only 5V as the input, the power will be lower than with 20V, so the battery will charge slower and the laptop may not turn on without battery or when the battery is discharged.
(From ISL9238 datasheet)
1.6. Battery voltage
Laptops battery packs are based around lithium cells.
These are either Li-ion cells, round cylinder similar to your alkaline battery but in a 18650 package, or LiPo cells, flat rectangular cell like in a smartphone.
Li-ion cells typically have a nominal voltage of 3.6V to 3.7V, LiPo cells typically have a nominal voltage of 3.7V to 3.85V. It varies depending on the brand and series of the cell.
The battery voltage and by extension the voltage used to charge the battery depends directly on how many cells there are in series inside the battery pack.
Battery packs can be described with a "xSyP" number, where y is the number of cells in a group connected in parallel, and x is the number of groups connected in series.
All cells in parallel in a group will have the same voltage across them. Putting groups in series will sum their voltages.
For example a 3S2P pack with 11.1V nominal voltage contains 6 cells, 3 groups in series of 2 cells in parallel, for a total voltage across the pack of 3x3.7V = 11.1V.
The number of cells put in parallel in a group helps increasing the capacity, but it doesn't change the voltage. We are interested in the voltage here, so we will ignore the cells in parallel.
The "nominal voltage" represents the voltage around which the cell is throughout most of its discharge, it should be what you are able to measure on the pack when it's charged to around 50%.
When charged fully, the voltage will be higher, when completely discharged, the voltage will be lower.
Charging voltage will be a bit higher than the fully charged voltage of the pack. For example, an 11.55V pack (3S of 3.85V nominal) can in general be charged at 13.1V (4.35V per cell). An 11.1V pack (3S of 3.7V nominal) can in general be charged at 12.6V (4.2V per cell). A 10.8V pack (3S of 3.6V nominal) can in general be charged at 12.3V (4.1V per cell).
This of course highly depends on the exact type of cells used, and using a voltage that's too high for a given cell type can at best damage the cell, at worst be a safety threat.
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