MOSFET H-bridge Voltage too low.
first of all, have circuit attached image. text file can imported java applet.
http://www.falstad.com/circuit/
the h-bridge performs expected logically. however, voltage drops across mosfets enormous. when i'm working 12v, ~5.5v drop across 2 transistors results in ~1v motor. intent @ least 9v motor.
which means there's fundamental mosfets i'm forgetting. can me troubleshoot this?
http://www.falstad.com/circuit/
the h-bridge performs expected logically. however, voltage drops across mosfets enormous. when i'm working 12v, ~5.5v drop across 2 transistors results in ~1v motor. intent @ least 9v motor.
which means there's fundamental mosfets i'm forgetting. can me troubleshoot this?
firstly you've used wrong symbols power mosfets, have an
integrated body-diode part of symbol. no need other diodes a
result. btw must distinquish source drain in power mosfet. you
need source power rail, drain motor in kind of bridge.
top-side switches p-channel, low-side n-channel logic-level.
the circuit wrong in various ways:
1) shoot-through - turn on mosfet on other turning off. this bad.
you must turn off 1 before other starts conducting otherwise large
current pulses flow through both mosfets, potentially destroying them , wasting a
lot of heat in them. must separately control high , low-side switches on
each leg of bridge , allow dead-time between switch-off , switch-on.
2) gate resistor. this should low in value, perhaps 0 ohms even... mosfet
gates highly capacitive, trying drive them 33k resistor result in
ultra-slow turn on , turn off times, dumping huge amounts of power wastefully
into them if pwm used. if driving mosfet direct arduino must
be logic level , wise use 150 ohm resistor protect arduino pin
from excessive current (the mosfet gate happily , usefully take more than
the arduino can supply while charging/discharging). something 1k or 470 ohms
for pull-up resistor on p-channel gate (limited heat dissipation
in resistor perhaps).
[btw actual devices using? how current motor
take under load , @ stall, what's rating of power supply?]
integrated body-diode part of symbol. no need other diodes a
result. btw must distinquish source drain in power mosfet. you
need source power rail, drain motor in kind of bridge.
top-side switches p-channel, low-side n-channel logic-level.
the circuit wrong in various ways:
1) shoot-through - turn on mosfet on other turning off. this bad.
you must turn off 1 before other starts conducting otherwise large
current pulses flow through both mosfets, potentially destroying them , wasting a
lot of heat in them. must separately control high , low-side switches on
each leg of bridge , allow dead-time between switch-off , switch-on.
2) gate resistor. this should low in value, perhaps 0 ohms even... mosfet
gates highly capacitive, trying drive them 33k resistor result in
ultra-slow turn on , turn off times, dumping huge amounts of power wastefully
into them if pwm used. if driving mosfet direct arduino must
be logic level , wise use 150 ohm resistor protect arduino pin
from excessive current (the mosfet gate happily , usefully take more than
the arduino can supply while charging/discharging). something 1k or 470 ohms
for pull-up resistor on p-channel gate (limited heat dissipation
in resistor perhaps).
[btw actual devices using? how current motor
take under load , @ stall, what's rating of power supply?]
Arduino Forum > Using Arduino > Motors, Mechanics, and Power (Moderator: fabioc84) > MOSFET H-bridge Voltage too low.
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