panic mode
- Joined Oct 10, 2011
- 2,751
to turn transistor on, you need some signal. for BJT that would be some base current, for mosfet that would be some gate voltage...
increasing (changing) that signal means transistor would conduct more current (this is used in amplifiers), basically transistor becomes controlled resistor. current through it becomes in some way related (proportional) to control signal.
but if we don't want this analog response. if we want transistor to work as a switch (full current), then we need larger input signal....
for power mosfets this usually means some 10-12V and maximum survivable gate voltage is usually some 20V. your mosfet is one of them. also the Vcc supply used for driver circuit is also 12V....
btw. few special mosfets are designed to be turned fully on using much lower voltage (3-5V) so they can be driven straight from logic gates (most logic gates operate at 5V or less). but not this mosfet...
now this explains what is required to turn the mosfet on, but there is more...
BJTs are connected in CC (common collector) configuration. this means the voltage gain is less than 1. in other words to get 10V out, you need to bring a bit more than 10V in (to base). although the voltage gain is less than spectacular, current gain is large and output impedance is low. this is exactly what one needs to charge/discharge gate capacitance fast.
increasing (changing) that signal means transistor would conduct more current (this is used in amplifiers), basically transistor becomes controlled resistor. current through it becomes in some way related (proportional) to control signal.
but if we don't want this analog response. if we want transistor to work as a switch (full current), then we need larger input signal....
for power mosfets this usually means some 10-12V and maximum survivable gate voltage is usually some 20V. your mosfet is one of them. also the Vcc supply used for driver circuit is also 12V....
btw. few special mosfets are designed to be turned fully on using much lower voltage (3-5V) so they can be driven straight from logic gates (most logic gates operate at 5V or less). but not this mosfet...
now this explains what is required to turn the mosfet on, but there is more...
BJTs are connected in CC (common collector) configuration. this means the voltage gain is less than 1. in other words to get 10V out, you need to bring a bit more than 10V in (to base). although the voltage gain is less than spectacular, current gain is large and output impedance is low. this is exactly what one needs to charge/discharge gate capacitance fast.