Charge pump principle handout, how is the voltage "pumped"?

Charge pump power supply is a common architecture power supply , Compared with inductor based switching power supply , The charge pump is small , There is no magnetic field and EMI interfere .

In recent years , The popular application of charge pump is fast charging in the field of mobile phones .

There are two fast charging schemes in the mobile phone industry: high voltage or high current , High voltage is simple and easy , Low requirements for accessories , If you consider reducing blood pressure , The efficiency is low ; The high current scheme has high efficiency , The requirements for accessories are also high , Especially wire , This leads to a sharp rise in costs .

High charge pump efficiency , The cost is low , Nature is widely favored .

The following figure is the basic architecture block diagram of charge pump , from 1 A flying capacitor Vc and 4 One switch can realize the basic charge pump function . First store energy for the capacitor , Then discharge the capacitor to the load , The following is a brief description of the working process of the charge pump .

The charge pump usually has two working states , Charge and discharge respectively , When charging , The path is shown in the figure below . When the switch Q1 and Q3 Conduction time , Flying capacitor C1 Charge , When the charge and discharge reach equilibrium , During the charging phase, there are ：Vi-Vc=Vo.

The discharge path is shown in the figure below , Capacitance during discharge C1 Directly to the load Ro discharge ,Vc=Vo, Combined with the formula when charging Vi-Vc=Vo, You can get Vo=0.5Vi, That is, the voltage is halved .

Multisim The topology of the simulation circuit is shown in the figure below

Take a look at the input 、 Output electric current , Relationship between input and output voltage , about ：

Io=2*Ii

Vo=0.5*Vi

That is, the voltage is halved , Current doubling

Look at the Ii and Io Current waveform , Red is the input current , Green is the output current , When the capacitor is charged ,Ii=Io=Ic, When the capacitor discharges ,Ii=0,Io=Ic. So throughout the cycle ,Ii There is only 1/2 A cycle ,Io There is a whole cycle ,Io=2Ii, Current doubling .

Finally, look at the charging and discharging , Red is the voltage across the flying capacitor , Green is the output voltage , The waveform is as follows ：

The above is the analysis and introduction of the basic working principle of charge pump .