I know flourescent lighting has come a long way since the days of bulky transformers and T12 lamps.
I cut open a dead electronic-ballast CFL to check out the components inside and I noticed the usual stuff: a few caps, a small x former, a few transistors, an IC, etc. I vaguely understand how they work but I'm still rusty on a few things.
Do they operate at AC or DC?
How do a few caps and a transistor convert line frequency into 20 Khz?
What voltage does the flour. tube operate at?
Are there any good diagrams on the net explaining how these work with notes describing the function of each component?
CT, I can run down some simple basics right now, and after the upload problems get fixed (and I finish this current Electrical Planset) will post a simple schematic of an Electronic Ballast. Picked up a Ballast at Advance Xformer when we did the new receptacle runs. The poor thing was clipped by a forklift - damaging the F Can and chopping off input leads, but the PC board and all components managed to escape the chaos! Can add some annotated pictures too.
Anyhow, I'll try and answer some Q's concisely:
The output to the CFL will be AC - High Frequency AC is the target goal. The line input 120 VAC @ 60 Hz is rectified to "somewhat straightline" DC. The rectifier is usually a full wave bridge type, and output filtering is normally a Capacitor only.
Most Electronic Ballasts will include AC line filtering and MOV crowbars in front of the 1st stage rectifier.
So, now that the power is "useable for Electronics" (DC), it gets inverted to a high frequency AC - via the larger heat sinked Transistors (the black plastic flat case with three leads). These FETs invert the DC into AC by being "turned on and off rapidly" via the clock circuitry (composed of the DIP type IC arrays). This results in an output AC which is somewhere between 20 kHz and 40 kHz - depending on who made the device.
The component which looks like a Transformer is a combination type Animal! It's both a Linear Reactor (Choke) and a Mag Amplifier / saturable reactor. On more intregrate circuitry for Electronic Ballasts, the reactor / amp is tuned via additional IC control circuit arrays. These systems integrate lamp control techniques - such as shutting off the Ballast if the lamp fails, lamp regulation, etc.
Output to a normal CFL would probably be around 200 - 300 VAC open circuit (what would be needed to start the lamp). After the arc inside the tube is setup, only a minimal voltage is found across the tube (maybe drops down as low as 2 volts, possibly 10 volts for a warm and well used lamp). Once the arc is established, things flow like mad!!! This is the primary function of the Ballast - to regulate the current flowing through the lamp, so it does not draw excessive current. The Negative Resistance situation encountered with an operating lamp will draw as much current it can get - until either the circuit can no longer supply additional / increased current, or the lamp fries it's self (lamps will generally fry them selves at about the same time a 20 amp breaker trips!).
Let me know if this was helpful enough to answer your Q's in a brief fashion (AKA: does this baloney make sense?).
Will try posting SMPS / High Hz Ballast info ASAP.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
#128385 - 02/10/0310:47 AMRe: How do Compact Flourescents work?