Adding a current limiting resistor at the base of the PNP seems to have solved the problem of the blowing regulator. I will now try to combine the NPN output and regulator output and see if it works
It could be the pnp is shorted or backwards. The 20 ohm resistor may need to be larger (watts) depending on the base resistor.Adding a current limiting resistor at the base of the PNP seems to have solved the problem of the blowing regulator. I will now try to combine the NPN output and regulator output and see if it works
Another simpler option:Ahh awesome thank ronv, this looks like it fits the bill . Any idea on how I go about deciding how much to limit the current on the primary winding and therefore my resistor value? Or is it a case of just keeping the secondary current below the surge current limit of my FWB rectifier?
Yeah it's a toroidal but it's 240V here unfortunately and I think that circuit was designed for 120V, if I used a 10 Ohm that would be 24 Amps which would trip my breaker and have me worried about my rectifier I could go with 48 Ohm 10W which would give me 5A and limit my secondary to 30A.I'd just try the 10 ohms so the current will be below the trip point of the breaker.
You have a toroid transformer?
http://forum.allaboutcircuits.com/threads/value-of-a-capacitor.122450/#post-982688Hey guys, Time for me to do a little follow up on this. Thanks for the inrush limiter circuit Ronv that work a treat and stopped the breaker going every time but the huge cap keeps it on for about 5 minutes after I switch it off, but that's no big deal
It works quite well with the inductive load I have designed it for but unfortunately I haven't got a resistive load I can use to test it with at the moment but I am assuming if it can handle an inductive load it should be ok with a resistive or capacitive. As expected the high voltage provided to the royer oscillator decreased heating time significantly.
One thing I am noticing though is that before a load is switched on the highest voltage measurable would be closer to 60V however once load is attached the maximum voltage decreases to the expected 52V approx. I can only assume that the voltmeter is measuring a peak value here before a load is applied. In addition to this when an inductive is switched on the voltage will drop very low and quickly increase to near the previously set value. I say near because it seems and inductive load slight skews my range of voltages, not by much but by some (5V max). I'm guessing this forced voltage drop is just due to the fact I can't change the current instantaneously in an inductor, but no damage to LM317 seems to result from this.
I chose some rather small emitter resistor values to balance my current load across the NPNs before realise the cable resistance is 4 milliohm per foot so I had to make the cable lengths match before attaching them to my resistor array.
Air flow in the unit is maintained by a LM383 PWM fan controller mounted on the top, inside the case with the respective thermistor behind the filter capacitor as this is the most likely area to encounter stagnant airflow. Four 40mm 0.12A axial fans mounted in opposite pairs maintain the airflow. The rear heat sink for the Power BJTs also has active forced air cooling (two 80mm axial fans) which are maintained by an additional fan controller with it's respective thermistor behind the heat sink and set low enough so ambient temperature increase is directly proportional to heat sink temperature.
So BIG thanks to the following members for helping me troubleshoot this and getting it going. I really appreciate it thanks
Ronv
Dodgedave
Lestraveled
Hp1729
Scottwang
Wbahn
I've attached the final schematic and some photos in case anyone is interested. As you can probably see I fell into my usual trap of barely leaving myself any room to fit it all in Also if anyone has any advice, suggestions or criticisms on the finished unit please feel free to comment, I would also appreciate this as I always make a list of refinements for future implementation (FYI that burned resistor did get replaced lol).
Thanks again everyone
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Thanks . If I remember correctly at 51.7V it drew around 5.2A with no work piece and with the bolt, after an initial low voltage-higher current draw (12A max till voltage increased) it settled at around the 7.5-8.5A mark.http://forum.allaboutcircuits.com/threads/value-of-a-capacitor.122450/#post-982688
Very nice!
Out of curiosity how much current does the heater draw with and without the bolt in it?
That will generate tons of heat.DC supply with an adjustable range of at least 30-50V @ 20A max.
I did consider this but I had trouble understanding how I could use a pre-tracking regulator with the pass transistors without all of the current passing through the pre-tracking regulator. The main function of the unit is to operate at maximum voltage and I just accepted at the time that the voltage differentiation would be indirectly proportional to the current available without burning out my transistors.That will generate tons of heat.
I would encourage you to think of a switching mode pre- or tracking regulator before the linear regulator.