# Inductor or ballast

1. Jul 25, 2009

### monus76

hi there
i just need to know , we use ballast of fluorescent lamp or ( inductor) in series ,i know it chokes the current ,so i just need to know what that choke means,does it increase the value of current ( means to say does it increase the charge transfer per unit time) or does it means it change the frequency or why not we use step up or step down transformer in parllel to supply rather that choke coil in series.

i know my question is little big,but i realy appeciate if someone reply.

with thanks

2. Jul 25, 2009

### Bob S

For ac currents, inductances (chokes) limit current in a fashion vaguely similar to resistors, but without the resultant power loss and heating. If you have a choke of 100 millihenrys in a circuit at 60 Hz (w= 2 pi 60 = 377 radians per second), the voltage drop at 1 amp is
V = jwL I = j 377*0.1*1 amp = j 37.7 volts.
The "j" indicates a phase shift of 90 degrees because chokes represent a reactive load instead of a resistive load. If you put this choke in series with a 25 ohm resistor, the impedance magnitude is
!Z! = sqrt(37.72 + 252) = 45.2 ohms