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The diodes will not ruin any regulation, 7805 will all the time have 5 volts in the output pin, the diodes are a easy way to solve the issue,the only thing can affect diodes is temperature, it cause to them to drop more or less than 0.7 volts... i will use 7805 as variable regulator but seems to nobody undertand voltage divisor in the ref pin of the 7805 and not honoring thevenin and norton theorems....a real good one will be to use a 2n3054 to drive the power and a zener for reference, but this guy is learning, and we cant get in to very complicated solutions....
any way , who cares now, the guy in need of the info is not posting any more....why dont even know the voltage output of the transformer.....i am getting more fun with my 230k volts 100 khz tesla coils....
The diodes will not ruin any regulation, 7805 will all the time have 5 volts in the output pin, the diodes are a easy way to solve the issue,the only thing can affect diodes is temperature, it cause to them to drop more or less than 0.7 volts... i will use 7805 as variable regulator but seems to nobody undertand voltage divisor in the ref pin of the 7805QUOTE]
The voltage drop across the diodes will vary with the current through them, and for a small current will hardly drop any voltage at all - regulation will be terrible!.
As for using the 7805 as a variable regulator, I'm sure almost everyone here knows perfectly well how to do it, and that it's not a very good option - for a start the current limiting no longer works!.
The output is only 5V.
An LM386 amplifier will have an output power into an 8 ohm speaker at clipping of only 113mW. Like headphones playing loudly. Flea power.
An LM386 amplifier won't work with a supply of only 3V.
Nigel. diodes are not resistors, they are two substrates of p and n silicon, they drop over them self 0.7 volts if they are silicon, not germanium(0.4volt ), independently of the current that flow thru them, they can have a variable voltage over them if they are polarity reversed and in alternate current, if you place them in pure dc voltage (with low or very lo ripple) no variable voltage is over them, other wise they will disipate power/
Nigel. diodes are not resistors, they are two substrates of p and n silicon, they drop over them self 0.7 volts if they are silicon, not germanium(0.4volt ), independently of the current that flow thru them, they can have a variable voltage over them if they are polarity reversed and in alternate current, if you place them in pure dc voltage (with low or very lo ripple) no variable voltage is over them, other wise they will disipate power/
actually no I tried it once for 12 volt to 3 volt and with my tester alone read 10-11 volts. diodes are in effect resistors or can be compared vaguely to resistors because their response is not linear like a resistor, the best bet is to just use the LM317 and if the original poster would put in the availanble voltage and current required it would help alot also the circuit diagram and the pcb posted have absolutely nothing to do with each other
I will have to go back to university, I did not know new semiconductor are resistors now...I know a pic can do thing that at my times I did with a 8031 an adc converter, a fifo and uart in one chip, but did not know about new diodes...
sorry for my poor knowlack of new stuff...
oh, my god....
The datasheet for any diode shows how much its forward voltage changes with changes in the current through it. From 0.25V at low current to 2V at high current. it is logarithmic.
The change in voltage ruins the voltage regulation if it is in series with the output of a regulator IC.
Did you realise that are milivolts? any way, again, i am giving a "get out of the problem" solution , I am not posting to try to help somebody that dont know much, of course is not the high tech solution..i suject the 2n3054 with a zener, but this guy burned a zener before, so bad idea, I sugested the lm317 and he only have a 7805, I sugested the voltage divisor in the ref pin of the 7805 to make the output varible, I even posted the formula to calculate it..but only I get post reply to say...diodes dont work...7805 cant get variable output, etc..I dont care, please , help the guy asking for help...and please, be wise...if you know thah you dont know everything you will progress in life, if you thing you seen all, know all, then you are gone, and not posthing , because the millions you made will have you in the bahamas with 10 girls arround...I am wrong?
Nigel. diodes are not resistors, they are two substrates of p and n silicon, they drop over them self 0.7 volts if they are silicon, not germanium(0.4volt ), independently of the current that flow thru them, they can have a variable voltage over them if they are polarity reversed and in alternate current, if you place them in pure dc voltage (with low or very lo ripple) no variable voltage is over them, other wise they will disipate power/
You appear severely deluded over how diodes work?, they dissipate power at all times, by the simple formula W = V x I - and, as I said, the voltage drop across them varies considerably with the current through them, the datasheet for the diode will show how much, and Audioguru has posted an example.
I'm presuming you're young?, and probably use simulators?, which probably imagine components as 'perfect' - this doesn't happen in the real world, and you have to design accordingly.
Did you realise that are milivolts? any way, again, i am giving a "get out of the problem" solution , I am not posting to try to help somebody that dont know much, of course is not the high tech solution..i suject the 2n3054 with a zener, but this guy burned a zener before, so bad idea, I sugested the lm317 and he only have a 7805, I sugested the voltage divisor in the ref pin of the 7805 to make the output varible, I even posted the formula to calculate it..but only I get post reply to say...diodes dont work...7805 cant get variable output, etc..I dont care, please , help the guy asking for help...and please, be wise...if you know thah you dont know everything you will progress in life, if you thing you seen all, know all, then you are gone, and not posthing , because the millions you made will have you in the bahamas with 10 girls arround...I am wrong?
There's no point posting suggestions that are completely rubbish and won't work, your diode suggestion, although crude, would work under certain specific circumstances - but would be badly regulated, and would output near 5V under very low load. The variable 7805 idea is absolutely useless - you can only INCREASE the voltage with that, your example allowing adjustment between 5V and 10V (assuming you could get 10V with the input voltage you put on the diagram).
Your best idea was a discrete zener/transistor regulator - the reason the OP 'burned' a zener is probably because he simply stuck it directly across the output!.
There's no point posting suggestions that are completely rubbish and won't work, your diode suggestion, although crude, would work under certain specific circumstances - but would be badly regulated, and would output near 5V under very low load. The variable 7805 idea is absolutely useless - you can only INCREASE the voltage with that, your example allowing adjustment between 5V and 10V (assuming you could get 10V with the input voltage you put on the diagram).
Your best idea was a discrete zener/transistor regulator - the reason the OP 'burned' a zener is probably because he simply stuck it directly across the output!.
After testing your advice I got the result which you will see it as an attachment file. But I need 3v from 5v regulator which is still elusive to me. I hope you will give me some light.
My components details :
Transformer - 9-0-9 Centre Type (From 220v AC)
Diode - IN4001
Capacitor(1) - 2200uf/25v
Capacitor(2) - 1000uf/35v
Regulator - LM7805
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