I've been looking at some of the layouts that require someting other than the usual -9V, +9V or +18V so after a few minutes of hunting for suitable power options I found these which look like they'll be perfect
One thing that does have me slightly concerned and confused though is that the 1n5817 diodes that are mentioned/suggested are only rated at 20V max? Which if they are to be used in a circuit to provide 25V or 33V seems to go against all the usual suggestions to make sure components are rated well above the supply voltage to make sure they don't expire in a spectacular way.
Haven't been able to find anything useful online so far (Mostly just links to these layouts) so a few questions......
First of all, how important is the voltage rating of the diodes in these circuits?
Are the diodes in non voltage critical part of the circuit?
If the voltage rating is important, what effect would substituting have? For example instead of 1N5817 (20V) use 1N5818 (30V) or 1N5819 (40V)
I got a big bag of 1N5819 for really cheap, and while they say they have slightly higher Fv, none of the ones I've tested seem to have any higher than 5817s.. That being said looking around at all the effects people make, you see 1N4002s and 4007s all over where a 4001 would work... people just built stuff with what they had. You won't notice a difference in 5819s and 5817s once you factor in a wall wart and peak power grid wall voltage being 116v or something etc..
As for 1N5817, I use them in charge pumps all the time, but never above 20v.. just get some 5818s or 19s :)
I agree! I use 1n4004 diodes, cause the local shop here sells them for very little money, once I bought like 500 of them for less than 10 bucks. They work fine for these kinds of tasks in place of the 5817 too.
perfect timing for Tayda order, tagged on some extra 1N4001, and added a bunch of 1N4002 and 1n5819 just for good measure.
I've seen mentioned that the 4001's may produce a bit more of a voltage drop compared to the 5817's but I think the possibility of maybe losing a couple of volts is a sacrifice I'm willing to make, especially if it means I have a safe circuit.
Once the parts arrive, and if all goes well I'll report back with some measurements for the different diodes
For the negligable time and cost to knock up a couple of extra boards, use the same IC and take measurements of each is something that I think might still be worthwhile to do, if only to get a legitimate comparison of the diodes. Of course measuring the caps beforehand would probably help to minimize variables as well, and if nothing else I'll have a couple of spare boards ready and waiting
The 1N400x diodes are all regular silicon power diodes with a voltage drop of about 0.7 V and the difference is in voltage rating: 1N4001 are rated for 50V peak reverse voltage, 35V rms reverse; 1N4002 are rated for 100V peak reverse, 70 rms reverse, and so on. You can get these ratings by reading the datasheet.
The 1N581x series are Schottky diodes with a voltage drop of about 0.3 V and different voltage ratings, 1N5817 is the lowest voltage, then 1N5818 and so on.
The way a charge pump voltage doubler works, the diodes are effectively one-way valves that allow 2 x V_supply to accumulate on a capacitor without discharging back toward the supply. So I think each individual diode is only likely to see 1 x V_supply of reverse voltage. However, it would be prudent to use diodes that are rated for the full output voltage just in case.
What you absolutely must be careful about is using an output supply cap rated for the full supply, with some margin of safety, so for the 33V charge pump circuit I would use an supply cap rated 50V or higher.
Hey Travis, thanks for reminding me of my emrarrasingly poor breadboarding skills something I really should put a bit more effort into I guess, along with following and understanding schematics. Mind you, this could well be a good incentive for me to try and get a bit better at it
3260 slot breadboard? isn't that a bakery?
Thanks for confirming that, I'd done some trawling around online and with the slightly patchy info I'd found, and my limited knowledge, I'd kinda figured out something like that might be going on (Each stage adds to the previous?) always nice to have it confirmed though I tend to use 35V or 50V caps as standard anyway, they're rarely any more expensive than lower ratings, and often the same size as well so nice safety margin for no compramise.
Could be a good idea to take measurements on all the diodes just to make sure of the voltages they see?
Looks like the diodes do see an increasing amount of voltage as you progress through the circuit, (Which is why I only did the first stage to 18V with the 5817's) and confirms that the increased voltage drop with the higher rated diodes is negligable, so hardly any compomise to use the 4001 / 4002 and you also have a far better safety margin.
From the measuremens I guess the 5817's are ok for an 18v charge pump, but for anything above that it would probably be a good idea to use the higher rated diodes.
With all the brilliant work and effort that others put into the site, the least I can do is give something back whenever my limited abalities allow, so it's a pleasure to be able to contribute something that might be of use to others