Lecture notes on charge pump principles: how is the voltage “pumped” up?

The charge pump power supply is a common power supply architecture. Compared with the inductor-based switching power supply, the charge pump is small in size and does not have the magnetic field and EMI interference caused by the inductor.

Reply from the WeChat public account: Charge pump simulation file

In recent years, the most popular application of charge pumps is fast charging in the mobile phone field.

There are two types of fast charging solutions in the mobile phone industry: high voltage or high current. High voltage is simple and easy to implement, with low requirements for accessories. If voltage reduction is taken into account, the efficiency is low. The high current solution is efficient and has high requirements for accessories, especially wires, which leads to a sharp increase in costs.

Charge pumps are highly efficient and low cost, making them popular.

The figure below is a basic block diagram of the charge pump architecture. The basic charge pump function can be realized by 1 flying capacitor Vc and 4 switches. First, the capacitor stores energy, and then the capacitor discharges to the load. The following briefly describes the working process of the charge pump.

The charge pump usually has two working states, namely charging and discharging. When charging, the path is shown in the figure below. When switches Q1 and Q3 are turned on, the flying capacitor C1 is charged. When the charge and discharge reach a balance, in the charging stage: Vi-Vc=Vo .

The discharge path is shown in the figure below. When discharging, capacitor C1 directly discharges to load Ro, Vc=Vo . Combined with the charging formula Vi-Vc=Vo, we can get Vo=0.5Vi, that is, the voltage is halved .

The Multisim simulation circuit topology is shown in the figure below. Reply to the WeChat public account backend: charge pump simulation file You can get the simulation source file based on Multisim.

Let's look at the relationship between input and output currents, and input and output voltages, which are approximately:

Io=2*Ii

Vo=0.5*Vi

That is, the voltage is halved and the current is doubled

Check the current waveforms of Ii and Io. The red one is the input current and the green one is the output current. When the capacitor is charged, Ii=Io=Ic. When the capacitor is discharged, Ii=0 and Io=Ic. So in the whole cycle, Ii only exists for 1/2 cycle, and Io exists for the whole cycle, Io=2Ii, and the current doubles.

Finally, when charging and discharging, the red color is the voltage across the flying capacitor, and the green color is the output voltage. The waveform is as follows:

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