I need to design a controller that can switch On and Off a line conducting high currents.
the power line: it is supplied by a banks of capacitors
the switch: it must close the circuit when a signal is given and stop it when another one comes.
the circuit will give a burst of current that may be a lot under the 1second of time, the timescale is in deciseconds or centiseconds
I was thinking to use a button for engage it and a beam-interruction sensor for disengage it.
Pushing the button will engage the capacitor banks that will magnetize a coil producing a high magnetic force over a piece of metal, when that piece moves in the tube an ir receiver will see that the ir led is covered by the metal and he will switch off the capacitors.
The control of the logic isn't a big problem, I can just use 1-2 little relays for control the switch.
I thought at a GTO thyristors but creating a negative current will be a handicap.
There are relays that can keep high currents?
the cheapest way? (I don't trust a lot transistors, they may suffer from magnetic field…etcc)
the capacitors will be 2-3 at 300-350 working volts at around 200-500 uF at the start, but they might be 3800uf at 68 V or lower.
I can use without any problems the GTO if the signals can come from a different power sources
what is the best way for solve that?
tank you
Giulio
Best Answer
This is requirement that could be easily met by many MOSFETS or IGBTs. A GTO thyristor is harder to control and need not be considered unless you have some special love of them.
If you do not trust properly designed and properly rated and properly constructed MOSFET (or IGBT) 'transistor' circuits then the following is of no value to you.
If you accept proper design will allow a highly reliable product to be built then read on.
Taking your worst case of 500 uF at 350V discharged in one centisecond.
Energy = 0.5 x C x V^2 = 30.625 Joule. Say 40 Joule = 40 Watt.seconds.
If discharged in 1 centisecond = 0.01 second then Wattage = 40/.01 = 4000 Watts.
At 350 V, i = W/V = 4000/350 = 11A.
There are many possible devices that would suit, but until more detail is available, here is an example device that should be suited.
IXYS IX50N60P3 600 Volt 50A N Channel MOSFET
In stock $7.40 /1
145 milliohm on resistance. Avalanche rated. 1 kW power rated (don't try it). Sensible TO247 package. Thermal resistance of 0.25 C/W.
The Rdson (on resistance) is pulse rated so lets make it 0.2 ohm. At say 12 A the dissipation is I^2.R = 12^2 x 0.2 ~= 30 Watts.
Case rise = 0.25 C/W x 30W = 7.5 degrees C.
Add heatsink as desired. Note that is for a continuous 12A and you are pulse discharging.
Care needs to be taken that all relevant facts are known. The above does not discuss energy handling at turn off - not hard, just needs designing.
If you can provide a more detailed description then a more detailed answer can be given, but the above shows that the task is entirely doable with off the shelf parts.