Electronic – How does the MAX232 double the voltage

capacitormax232rs232voltage-doubler

MAX232 Datasheet

Hi, I am currently a student so bear with me please!

I'm currently using a powering the MAX232 with 5V DC, and when I measure from VCC to lets say, pin 3, I am getting a voltage reading of around 13V on my voltmeter. Using a power source that is higher than 5V. What is going on? I know it says in the datasheet that there is a voltage doubler, but I am not quite sure how voltage doublers work, other than we need the capacitor.

Best Answer

It uses one charge pump to double the supply voltage, and the second charge pump to invert it. The idea behind the charge pump doubler is that capacitors are first charged in parallel, then they are switched such that they are connected in series.

enter image description here (Source of picture: datasheet for ICL232, which is similar to MAX232.)

As an aside, I've seen hacks where +10V and -10V generated by the MAX232 were also used as supply rails for OpAmps. It's not the best power supply, and it's got switching noise from the charge pump. But it may still work, if the analog section is not very sensitive, and it needs a negative supply rail, and there is no other option for generating the negative supply rail.

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