This work is licensed under a Creative Commons License and is copyrighted 2004 by Michael Robinson
Pulse Forming Network (PFN)
The PFN, or Pulse Forming Network, provides power to the flashlamps in the proper pulse form. The following formulas help you design a PFN compatible with your flashlamps.
Deciphering Variables
The variables required in the following formulas are measurements of your flashlamps and PFN. Below is a summary of each measurment:
a = 0.8 for critical dampening
A = crossection of the flashlamp's internal bore (cm squared)
c = capacitance (farads)
Eo = energy (joules)
i = transformer current (amps)
I = home current (amps)
Ipk = peak current (amps)
Ko = flashlamp impedence; total impedence if there's more than one lamp (ohms)
l = flashlamp arc length between the two electrodes (mm)
L = inductance (henries)
p = laser power requirement (watts)
P = flashlamp sensitivity
V = home voltage (volts)
Vo = initial voltage (volts)
t = (t ^ 1/3) / 3; circuit time (seconds)
t^1/3 = pulse width (seconds)
T = pulse rate; width between pulses (seconds)
Zo = (L/c) ^ 1/2; circuit impedence (ohms)
Capacitance
c = ((2 * Eo * (a ^ 4) * t ^ 2) / (Ko ^ 4)) ^ 1/3
Credit goes to "Sam's Laser FAQ" for the original version of this formula.
Example for the Ruby project:
c = ((2 * 3000 * (0.8 ^ 4) * .00053 ^ 2) / (172.8 ^ 4)) ^ 1/3
Capacitance = .000092 farads (92 microfarads)
Inductance
L = (t ^ 2) / c
Credit goes to "Sam's Laser FAQ" for this formula.
Example for the Ruby project:
L = (.00053 ^ 2) / .000092
Inductance = .003 henries (3 millihenries)
Initial Voltage
Vo = ((2 * Eo) / c) ^ 1/2
Credit goes to "Sam's Laser FAQ" for this formula.
Example for the Ruby project:
Vo = ((2 * 3000) / .000092) ^ 1/2
Voltage = 8075.73 volts
Peak Current
Ipk = Vo / (Zo + (P * (1/A)))
Credit goes to "Sam's Laser FAQ" for the original version of this formula.
Example for the Ruby project:
Ipk = 8075.73 / (5.71 + (0.02 * (90/1.257)))
Peak Current = 1130.7 amps
Questions
Question: What pulse width and pulse rate should I setup my Ruby laser for?
Answer: Your pulse width and pulse rate are greatly determined by the current available from your home wiring, the available transformers, and the lasers application. Most home wiring can only supply up to 15A, transformer selection is usually limited to 9000V 30ma neon sign transformers, and cutting laser require a high pulse rate and width, while holography doesn't. - Michael Robinson
This work is licensed under a Creative Commons License and is copyrighted 2004 by Michael Robinson