![]() ![]() Consider undervoltage lockout if you use such a small package since the consequences of it turning partly on can be disastrous. For example, it may be rated for 2.5V drive, but Rds(on) quoted with 4.5V drive.įor example, a quick search comes up with the Si3442CDV. The parametric search is sloppy enough that you may have to go through several datasheets to be sure. Also pick one with sufficient voltage capability (3.3V + one diode drop for the flyback diode), sufficient maximum current for the stalled condition. Better 0.1 ohm to account for temperature. For example, for a 1A motor you might want < 150mV drop so Rds(on) < 0.15\$\Omega\$ with 3V drive. For 3.3V drive you should pick one that is rated with 2.5V or 1.8V or 0.9V Vgs and look for a guaranteed Rds(on) at < 3V Vgs that is sufficiently low. You can search distributors using parametric search. ![]() The voltage drop is too high (At 3A the voltage drop could be as much as 2V, but at 2A it's typically a bit over 1V- even so it takes about 1/3 of the motor voltage typically). See for example these tutorials on how to use nFETs as a switch:Ī Darlington is not a very good way to drive a motor from 3.3V. This is especially problematic if you are operating at high currents and low voltages. Between collector and emitter of a Darlington transistor you will always lose around 1.2 V, no matter how much current you are switching. MOSFET can often be just as easy (or even simpler) to use and losses at the transistor will be smaller. If you switch a low voltage load, e.g.: a single LED, a motor running at 3.3 V volts, then bipolar transistors and especially darlingtons will be very ineffective. Using a Darlington transistor can be effective for loads with a high voltage that are switched often, but are only switch on for a short time. You might need to reduce the resistance your base resistor a bit at 3.3V. The resistor between your micro controller and the TIP120 will convert the voltage to a current. You do not apply a voltage to a bipolar transistors base, but you apply a current to the base. ![]()
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