# Switched Capacitor Battery Charger?

#### CleverCKT

Joined Dec 14, 2017
2
Does anyone know of any commercial (or otherwise) battery chargers that use a switched capacitor circuit (i.e. 2:1, Dickinson, charge pump, etc)?

I know they are used as voltage supplies for digital chips and such, but all I've seen are inductor based topologies for actual battery charging.

Is their lack of popularity due to current regulation issues?

Thanks!

#### MSFTF

Joined Aug 11, 2017
33
It might be that using a transformer could tend to be an easier way to get isolation. However, I imagine that using a very small capacitor in a switching circuit could result in effectively having isolation.

#### tcmtech

Joined Nov 4, 2013
2,867
What size of battery and what is the power source and why do you think a charge pump is a good idea to begin with?

Usually when something is done a certain way that's because it's the cheapest most effective way to do it with.

#### DickCappels

Joined Aug 21, 2008
8,685
(some text removed for clarity)
Is their lack of popularity due to current regulation issues?

Thanks!
That is why is sounds to me like it would be a poor choice.

#### OBW0549

Joined Mar 2, 2015
3,566
Is their lack of popularity due to current regulation issues?
Probably not, since the output current vs.voltage (i.e., the effective output impedance) of a switched-capacitor converter can easily be adjusted simply by changing the switching frequency.

More likely, the problem is their power inefficiency: although switched-capacitor converters can achieve very high efficiencies, they can do so only if their output voltage is an integer multiple of their input voltage (Vout = 2*Vin, Vout = 3*Vin, Vout = -1*Vin, etc.) or an integer fraction (Vout = Vin/2, Vout = Vin/3, etc.).

For any intermediate output voltage, either the switching frequency must be adjusted, or the switching circuit must be followed by a linear voltage regulator. In both cases, the power conversion efficiency becomes no better than if a linear regulator had been used instead of a switching converter in the first place.

Inductor-based voltage converters, on the other hand, can achieve high power conversion efficiencies regardless of the ratio of output voltage to input voltage, and I think this is why you see them much more often used in battery charger designs than switched-capacitor converters.