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Registered Member #3358
Joined: Mon Oct 25 2010, 09:47AM
Location:
Posts: 20
I'm sure there is something wrong with this circuit here. the lm311 is backwards between the circuit diagram and the pcb template. any help would be greatly appreciated
For reference with the pcb : Cap1 10nF Cap2 1nF Cap3 100uF Diode1 Green LED Diode2 SFA1608G power inductor1 130uH channel transistor1 IRFP450 Resist1 15k Resist2 4.7k Resist3 15k Resist4 68 Resist5 15k Resist6 15k Resist7 12k Resist8 10k Resist9 1M Resist10 1k U1 NE555 U2 LM311 W1 Ground (In) W2 12V in W3 Ground (Cap Bank) W4 Capacitor Bank +
Registered Member #3358
Joined: Mon Oct 25 2010, 09:47AM
Location:
Posts: 20
wats really bugging me is that the led signals complete charge of the capacitor bank but instead it turns on the second the power is on. i have no idea why as well which is annoying me
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
It looks fine to me, though I haven't actually tried that layout myself. Remember the layout is placed ink-side down onto the PCB, so you can just place the LM311 on top to confirm that the layout makes sense. You've written +3V on the image, keep in mind the LM311 needs at least 3,5V to operate. The voltage range shown beside the potentiometer assumes 12V operation. The exact stopping voltage will depend on the voltage of your battery, since the comparator simply uses a voltage divider.
To be honest it's a terrible design, and one I've wanted to improve for a long time. If I get some time during the next few days I'll try to come up with something smarter.
Registered Member #3358
Joined: Mon Oct 25 2010, 09:47AM
Location:
Posts: 20
Yea it doesnt seem great to me but i dont know enough about electronics atm to make a better one myself. If you got any leads on how to though i'd greatly appreciate any information.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
One very easy upgrade would be to add a gate driver between the 555 and the power transistor. This would make it much less dissipative, since the 555 doesn't have enough power to quickly switch the gate.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Nothing more than a low side 1A or more ic. It's by no means a heavy load to drive a single 450/460 fet at moderately low speeds.
As for a better circuit, this is just a boost converter to charge a cap. If you where using the cap for filtering and running a hvdc power source, then you would be needing a true drive circuit with current sensing and pulse width. But in this application, a 555 is sufficient.
Eirik, if you do go designing a new version, give the sg3525 a shot where the pulse widths is controlled by the feedback.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
That's a common misconception, but the gate is switched fast enough for this application. The circuit is only operating an inductive load at 4kHz, but if you want put a diode in reverse parallel with the 68R resistor for faster turn-off. The fix I had in mind was using a current-mode controller IC instead of a 555. The would prevent problems like inductor saturation or excessive current in the switching device.
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confusing circuit
