You can also make a red flashlight from scratch using a single red LED, a 10-ohm dropping resistor
in a series with the 1K (or even 2K) potentiometer, and any kind of handle that will hold two or three 1.
The magnetic field was excited by a pulsed current without a dropping resistor.
The magnetic field was excited by a pulsed current without a dropping resistor, and by a constant current with a dropping resistor (R = 2 Ohms).
One of the drawbacks of existing Darlington amplifier solutions, however, is the need for an external dropping resistor for setting and stabilizing the bias current of the amplifier.
bias] dropping resistor and are currently offered in the popular SOT89 package.
Operation directly from a 3-volt or 5-volt supply with no dropping resistor
A dropping resistor
from the DC bus initiates start-up current for the IRIS4009.
The ability to to deliver up to 4 settings of speeds or variable speeds without the use of dropping resistors
The patented self-bias topology allows designers to easily integrate into single-supply, 5 Volt applications without the need for any external dropping resistors
The low start-up current substantially reduces dissipation in any dropping resistors
required for start-up of the part, while the minimized operating current drastically cuts the amount of power that must be supplied to a SiP280x controller merely to power the IC.