Join Barron Stone for an in-depth discussion in this video BJT vs. MOSFET, part of Electronics Foundations: Semiconductor Devices.
- [Lecturer] Although BJTs and MOSFETs can be used for similar purposes they are different types of transistors that work in different ways and each have their own set of pros and cons. Deciding whether to use a BJT or a MOSFET for certain projects can be a bit of a struggle and unfortunately there isn't a straightforward answer for which one is best to use, it depends on what you're doing. So, to help with planning your next electronics project I'll discuss some of the pros and cons of each one.
BJTs tend to have better, more linear gain characteristics and can give you a lot higher voltage gain than MOSFETs. They're also able to handle higher output currents and have a lower output impedance. That gives BJTs a huge advantage over MOSFETs for building amplifier circuits that need to provide a significant amount of output power and or drive loads that have low input impedance. MOSFETs are going to have a harder time driving a low impedance load because they have a higher output impedance.
That said, the advantage of MOSFETs is that they have a very high input impedance, so it's easier to couple them with a signal source that has a higher output impedance. Trying to connect a BJT amplifier to a high impedance signal source can cause problems, because the BJT has a lower input impedance. Another advantage of MOSFETs is that since they're voltage controlled rather than current controlled they usually consume less power than a BJT.
A MOSFET doesn't require any current to flow through its gate terminal to operate, but a BJT consumes base current whenever it's turned on. That power efficiency can make MOSFETs more desirable for battery-powered applications, where every little bit of power that gets spent matters, especially when the load that it's controlling is variable and could have a low impedance. However, for controlling a load that draws a fairly small and predictable amount of current, like an LED, using a BJT isn't all that bad.
You can choose the right limiting resistor to keep the base current as small as possible to achieve a reasonable efficiency. When directly driving a transistor with the 3.3 or five volt output from a microcontroller it's usually easier to find BJTs that can turn with those voltages than MOSFETs, because MOSFETs usually require a gate-to-source voltage of at least 10 volts to fully turn on. That makes BJTs the better choice for driving low-powered devices directly from microcontrollers and BJTs will usually be cheaper than the corresponding MOSFET that can do that same job.
For high power applications, driving loads that require significant and variable amounts of current, like a large motor, MOSFETs are generally the better choice.
- Semiconductor materials
- Diode applications
- Rectifying a signal
- Detecting the signal peak
- Protecting against large signals, reverse current, and flyback voltage
- Special purpose zener diodes, Schottky diodes, and photodiodes
- NPN and PNP bipolar junction transistors
- Using a BJT as a switch
- Field effect transistors
- Differences between BJTs and MOSFETs
- Operational amplifiers
- Op-amp applications
- Comparing signals
- Buffering signals
- Amplifying signals
- Filtering signals
- Combining signals