Understanding Laptop Power Supplies & Inventers

Thread Starter

Management

Joined Sep 18, 2007
306
Hi Everyone,

I would like to inquire about laptops and the electronics in them.

I know laptops can be charged while they are in use but what enables this to happen?

I know there is a AC to DC rectifier in the power cord and then I know there is some DC to DC power supplies (and regulators) on the motherboard. But,

what controls the fact that I can charge the battery (especially while it's dead) and use the laptop so seamlessly? I figured the laptop as a whole is drawing more power from the mains to make this happen.

what allows for the battery to die or be disconnected without experiencing any severe interruption in power when the AC supply is connected?

Looking for the technical details on what is enabling this to be possible. Thanks!
 
Last edited:

kubeek

Joined Sep 20, 2005
5,794
Basically you have two diodes, one from from adaptor going to the notebook supplies, and another going from the battery to the notebook supplies. When you have either a battery or adaptor connected, the notebook lives.

The actual circuitry is much more comlicated, but the basic idea stays.
 

crutschow

Joined Mar 14, 2008
34,285
Basically you have two diodes, one from from adaptor going to the notebook supplies, and another going from the battery to the notebook supplies. When you have either a battery or adaptor connected, the notebook lives.

The actual circuitry is much more comlicated, but the basic idea stays.
Don't forget the charging circuit going from the adapter to the battery.
 

Thread Starter

Management

Joined Sep 18, 2007
306
Basically you have two diodes, one from from adaptor going to the notebook supplies, and another going from the battery to the notebook supplies. When you have either a battery or adaptor connected, the notebook lives.

The actual circuitry is much more comlicated, but the basic idea stays.
Can everyone elaborate in some more detail?

This assumes only one is connected at a time. But how do they work together to charge and supply power to the laptop? Does the battery supply power while the AC mains charges the battery? Or does the battery get charged and remains unused while the AC adapter is disconnected? I assume the latter but how? What controls this, diodes?

I think this doesn't happen but is it possible (practical?) to supply power to the laptop from both sources when not enough power is available from the AC plug (supply)?
 

Thread Starter

Management

Joined Sep 18, 2007
306
I wanted to point out that AC to DC uses a rectifier, DC to AC uses an inverter...
Thanks! I actually didn't notice I did wrote that. A little brain fart on my end.

Whats more expensive ... a rectifier or inverter? Roughly speaking in terms of complication.
 

tshuck

Joined Oct 18, 2012
3,534
Thanks! I actually didn't notice I did wrote that. A little brain fart on my end.

Whats more expensive ... a rectifier or inverter? Roughly speaking in terms of complication.
Inverter by a lot.... A rectifier can be built with a single diode(pretty poor quality, but a rectifier nonetheless..)
 

Thread Starter

Management

Joined Sep 18, 2007
306
Inverter by a lot.... A rectifier can be built with a single diode(pretty poor quality, but a rectifier nonetheless..)
I understand that but I'm just trying to understand roughly if one is known to be cheaper or not lumped sum of various factors (of which I don't know hehe)
 

toffee_pie

Joined Oct 31, 2009
235
why does a laptop need an inverter?

the power supply is a AC-DC regulator, Switch mode supply.

all the laptop wants is DC. whether from the Battery, regulated by a BMS or from the brick supply.
 

Thread Starter

Management

Joined Sep 18, 2007
306
why does a laptop need an inverter?

the power supply is a AC-DC regulator, Switch mode supply.

all the laptop wants is DC. whether from the Battery, regulated by a BMS or from the brick supply.
No offense but if your going to contribute please read the entire thread.

No one is suggesting that laptops need inverters or using inverters inside a laptop.
 

crutschow

Joined Mar 14, 2008
34,285
Many modern AC to DC converters also use a switching inverter for smaller size (due to much reduced transformer size) and better efficiency.
 

toffee_pie

Joined Oct 31, 2009
235
well thats apple for you...

its generally good practice to NOT have a battery when its not used, since the heat will do li-ion cells more harm than good
 
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