Let's Make Robots!

ok ok i'm building a voltage reg...erm help?

hi peeps

ive decided to build the voltage regulator board but im clueless about the voltages

ill be using a TS 7805 CZ reg , a larger capacitor in front and a smaller one after ... but how do i decide on the capacitor size?

i want a steady 5v supply for my machine and i have a choice of 6 rechargeable AA batteries (7.2v) or 8 AA's (9.6v) ... i'd prefer to use the 7.2v as i could swap it later for some battery packs i have (when i find a way to charge em) but it just makes the 2.0v vdrop... whereas the 9.6v version makes the 2/3 vdrop some peeps say is better...

any idea's?

oh and could you explain how you came to the conclusion as i'm more used to biological fluid logic rather than maths based logic.

thanks peeps


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The cap will discharge itself very quickly if the load (voltage reg.) is still connected after the power is removed.

The cool thing about the latch is that when the Zener triggers transistor #1, transistor #2 gets switched on by transistor #1 as well. Then, because the two transistors are connected back to back, transistor #2 works in parallel with the Zener to keep transistor #1 turned on.
Since transistor #1 is now keeping transistor #2 active and vice versa, the latch created by the complementary transistor pair will stay on (latched) until power is removed, even if the supply voltage falls below the Zener threshold.

If you set the circuit up so the Zener switches transistor #1 on only when the cap is almost at full charge, you should get the delayed start effect as intended, without having to worry about the timing being incorrect.

i'll have another look to try and decode what you just said (after all the whole point of project blue beta is to learn)


i woke up the other morning thinking "why not just put a ceramic capacitor between the electrolytic one and the volt reg to smooth out the fluctuations" (i do that a lot - i must dream in tech).

so i used my new soldering iron to stabilise the connections of all the various parts rather than doing it breadboard style then hooked it up to the multimeter - and suddenly there was no fluctuation - not sure if its because of the soldering or if its no longer an unused capacitor but the problem seems to have sorted itself out for now

do electrolytic caps hold onto a residue after thier first charge or get altered in some way that makes later use smoother?

(i doubt it was the soldering if i'm honest as i was pretty carefull first time about the connections - but the scientist in me never likes to leave out a possible affecting circumstance)


Multiple capacitors connected in parallel will tend to behave like a single capacitor, but with capacitance equal to the total sum of the capacitances. This isn't always exactly how it works, especially with diferent types of capacitors connected together, but the real deal is usually pretty close.

I know electrolytic capacitors tend to lose their capacitance as they age, but I haven't heard of them having to warm up or anything like that when you first use them. I think they'd probably charge and discharge them a few times when first manufactured, but maybe that's only done for the high performance electrolytics use in PCs and such.

Either way I'm glad your problem has been sorted out =)
Maybe the new soldering iron was the trick? Cold solder joints can have very poor conductivity even if they look ok on the outside.

the caps combine? bugger...there goes that understanding (i was hoping to smooth one using another) - it does make sense tho i suppose.

the caps im using were given to me at my first attempt (amber alpha?) at electronics about ten years ago by my little bro who worked at Tandy when it went bust so i dunno if age was a factor

thanks for your help tho - i can feel my brain getting bigger every day thanks to you lot and your advice (might explain the headaches and the goo oozing from my ears)