On 7 Aug 2011, at 19:02, Eric1180 wrote:
I plan on using a 555 or a AP34063 and i have a IRF510. But i don't know what to adjust to get the voltage down. I think the plans you use to make Nixie power supplies are called MK1.5 or MK2. it would be easier to figure out what to adjust if i have a IRF710 and...
I can tell you that the standard 555 circuit that works for nixies works just fine for VFDs too, if you adjust those two feedback divider resistors. I can look up what I used before for you, if needs be.
Most VFD circuits end up being multiplexed in some way, but you may be driving individual tubes of some unspecified kind, directly. You don't always know what final voltage you need, so some variable resistor in that feedback divider is very useful. Once you know what values work for your setup, you could replace them with fixed values. Unless you need to be able to adjust brightness to suit ambient changes in lighting.
...and i could just tinker around till i find out what controls the voltage but since the IRF510 Transistor i have cant handle 170v i don't know what to adjust.
Sorry? What VFDs are you driving that need 170v? Most kick in at around 25v, but often might need around 40v if you are multiplexing a set of tubes, or one of the Russian IV-18 type 9-digits-in-one-tube kind of a VFD setup.
As always, you will get more help from the group if you state what exactly you have and are trying to do with the parts at your disposal. This group is a mine of information, most of it very useful, always entertaining.
The best idea I saw so far was one Chris 'Fixitsan' Barron came up with. His concept used a PIC's PWM output to drive the FET. The feedback voltage was measured by the PIC and the duty cycle of the PWM pulse increased until the voltage was seen to decrease again, indicating saturation of the FET. The mark/space duty cycle ratio is then backed off a few pips and the system has thus self-optimised its efficiency. This system could cater automatically for a range of differing inductor values.
In fairness, and if my memory is correct, Nicko, our chief moderator, suggested that driving a FET from a PIC output could stress the PIC output gate in ways a PIC didn't ought to be stressed and that current sensing and back EMF diodes should be incorporated. I am not the right person to speak about such things but I for one would appreciate a lesson from the experts in this group on such a topic.
In balance I should say that I have seen a variety of nixie clock kits, pre-built or otherwise, driving FETs from a PIC gate so I suspect they work just fine. Has anyone experience of these causing long-term issues for the PIC in any way?
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