However, all these super features come with a cost. I understand the princible of the capacitor voltage rising when you apply a voltage to the grounded side now though, quite a clever concept! Originally Posted by FvM. That would provide a nice context. Otherwise, MOSFET can get damaged as this parasitic capacitor will keep on charging and will exceed the limit of the gate to source breakdown voltage.

Uploader: Shakaran
Date Added: 1 August 2006
File Size: 68.88 Mb
Operating Systems: Windows NT/2000/XP/2003/2003/7/8/10 MacOS 10/X
Downloads: 96810
Price: Free* [*Free Regsitration Required]

Bootstrap MOSFET explanation

I hope you don’t mind me butting in. The signal is received through the output of another optocoupler Shown as opt2 in the circuit diagram which receives PWM by connecting its input pin to the pin 3 of the Arduino. One pair can drive the N-channel M3. Refer the datasheet of the MCT2E optocoupler for checking its technical specifications. Dan Laks 7, 3 nmis Sign up or log in Sign up using Google. This action is nmks bootstrapping because raising the voltage at one end of bootatrap capacitor also raises the voltage at the other end just as pulling the end of a shoelace bootstrap transfers the tension though the holes to the lower end.

Shortbus, saying ‘You also have it wrong. Thanks for setting us right. In the domain of MOSFET circuits, “bootstrapping” is commonly used to mean pulling up the operating point of a transistor above the power supply rail.


I’m at a loss to further explain it. How can a source terminal be ‘on’? I would be really happy if you could provide some example with a circuit.

Driving High Side MOSFET using Bootstrap Circuitry – (Part 17/17) | EngineersGarage

What I’m trying to get at is that the gate voltage never goes above its original voltage, in this example 15V. Feel free to correct me if I’m wrong. I am juist curious as to how the bootstrap circuit creates a voltage potential botstrap is 15V higer than the highest supply potential in the circuit.

The capacitor C1 now tries to maintain the 12V across it and this raises the source voltage to 12V. Nov 1, I only learned the concept last Thursday, but I’m fairly sure that’s how it works. Output Feedback Control Method.

And I don’t want to use any driver IC to drive the mosfet gate. Although there are some features common to different kinds of bootstrap circuits, they don’t bring you far in explaining the specific circuit operation. The box marked as just “driver” in the image. To generate that high voltage, a bootstrap circuit is used. Since a good driver pushes and pulls large amounts of current, it makes sense that another pair of transistors exist within the IC to drive the VH pin high or low.


This is seldom done deliberately, however, and is normally an unwanted result of a particular circuit design. Hello my friend The technique to provide very high input impedancecalled boot strap. The transistor is turned off by opening the capacitor switch and connecting the gate to the source with another switch. In practice, the current they can provide is not enough for driving a MOSFET fast; so they need additional circuitry in practice. Most control schemes that use a bootstrap capacitor force the high side driver N-MOSFET off for a minimum time to allow for the capacitor to refill.

This reduces the voltage difference between Vcc and point 2 and thus reduces the available base current to Q2. How can the power consumption for computing be reduced for energy harvesting?

Email Required, but never shown. Some form of self-driven charge-pump configuration is used to generate this higher-than-supply voltage across a storage capacitor, otherwise known as the bootstrap capacitor, to power the high-side NMOS driver.

Emitter followers can provide rail-to-rail output in this way, which is a common technique in class AB audio amplifiers.