You have 12,6 AC transformer right...so then you have to rectify it...and smooth it with a cap..will get you to around 16V..
That is enough to use a 7812. Remember it needs more voltage than 12,6V to be able to give 12 regulated.
The 7812 is fixed at 12v out regulated...so you need no trim!
Why did you post this at in the Tubes section by the way?
Cheers,
Bas
That is enough to use a 7812. Remember it needs more voltage than 12,6V to be able to give 12 regulated.
The 7812 is fixed at 12v out regulated...so you need no trim!
Why did you post this at in the Tubes section by the way?
Cheers,
Bas
How much current (DC) will you need? And how much current totally?
You cant get 1A 12 DC from this winding , maybe 0,7A .
And to load a 7812 with 1A is in the danger zoone, and it probably will get very hot.
Is it for DC heater to one or two tubes ? Then I say you'd better throw in a diode from pin two (and that is the case too) to - (might be the ground) as EC8010 suggest.
björn
You cant get 1A 12 DC from this winding , maybe 0,7A .
And to load a 7812 with 1A is in the danger zoone, and it probably will get very hot.
Is it for DC heater to one or two tubes ? Then I say you'd better throw in a diode from pin two (and that is the case too) to - (might be the ground) as EC8010 suggest.
björn
hi, thanks for your replys
in fact it is for the relay board of my tube preamp, which relays are 12V, i guess i am more concerned with tube amps that s why i ve been using this forum and not another, sorry
so i ve bought a transfo for a ridiculous price to make my preamp and i have one 12.6V 1A output left after building the preamp, and i want to use it to drive my relay board, which relays are 12V,
so i ve been picking up a relay board scheme from a magazine which has a 7812 regulator feeded with 12V and i ask this question because i want to use my 12.6V output to feed the 7812
so hello Bas, can you explain me how can i rectify my transformer?
by the way here is a picture of the preamp, it is a 6 ch preamp
cheers
fred
in fact it is for the relay board of my tube preamp, which relays are 12V, i guess i am more concerned with tube amps that s why i ve been using this forum and not another, sorry
so i ve bought a transfo for a ridiculous price to make my preamp and i have one 12.6V 1A output left after building the preamp, and i want to use it to drive my relay board, which relays are 12V,
so i ve been picking up a relay board scheme from a magazine which has a 7812 regulator feeded with 12V and i ask this question because i want to use my 12.6V output to feed the 7812
so hello Bas, can you explain me how can i rectify my transformer?
by the way here is a picture of the preamp, it is a 6 ch preamp
An externally hosted image should be here but it was not working when we last tested it.
cheers
fred
12 V regulator
Yes, the 7812 produces a regulated 12V output, but needs a higher, rectified voltage which is at least 14.5 volts at the input, NOT the output of the transformer directly. Good news is, all of these parts are cheap compared to your trafo.
So: unregulated DC in, regulated 12V DC out.
I would say first add the currents for all of the relay coils that can be on at the same time, to calculate the maximum current needed. That will be the worst case for the DC regulator, and it will allow you to calculate if you need a heatsink (you can also use more than one 7812, they are cheap enough).
The AC output of the transformer is rectified first, using a bridge rectifier, or four diodes, followed by one or two capacitors. This gives you the so-called un-regulated supply somewhere between 14 and 18 volts DC, depending on your transformer and the load etc. You need about 14.5V with this part to maintain regulation, but this is not so critical with relays. Then the 7812 regulator, with or w/o heatsink.
Whether you need a heatsink for a linear regulator can usually be calculated based on the type of case (TO-220 here), the voltage across the regulator, and the maximum current. There is probably a formula for this in the 7812 datasheet.
Wild guess: for this transformer voltage and 1A out, you need a bridge rectifier rated at 1-3 amps, 2 or three cheap electrolytic capacitors around 2200-3300uF each and rated at 25 volts minimum, and a heatsink rated at 10 degrees C/watt for the regulator.
Nice picture, btw.
PM
Yes, the 7812 produces a regulated 12V output, but needs a higher, rectified voltage which is at least 14.5 volts at the input, NOT the output of the transformer directly. Good news is, all of these parts are cheap compared to your trafo.
So: unregulated DC in, regulated 12V DC out.
I would say first add the currents for all of the relay coils that can be on at the same time, to calculate the maximum current needed. That will be the worst case for the DC regulator, and it will allow you to calculate if you need a heatsink (you can also use more than one 7812, they are cheap enough).
The AC output of the transformer is rectified first, using a bridge rectifier, or four diodes, followed by one or two capacitors. This gives you the so-called un-regulated supply somewhere between 14 and 18 volts DC, depending on your transformer and the load etc. You need about 14.5V with this part to maintain regulation, but this is not so critical with relays. Then the 7812 regulator, with or w/o heatsink.
Whether you need a heatsink for a linear regulator can usually be calculated based on the type of case (TO-220 here), the voltage across the regulator, and the maximum current. There is probably a formula for this in the 7812 datasheet.
Wild guess: for this transformer voltage and 1A out, you need a bridge rectifier rated at 1-3 amps, 2 or three cheap electrolytic capacitors around 2200-3300uF each and rated at 25 volts minimum, and a heatsink rated at 10 degrees C/watt for the regulator.
Nice picture, btw.
PM
thank you Bas and PMiczek 
Bas, for the diagram, it looks familiar to me now, thanks
concerning the caps, should i use one 2.2microF 25V, like on the diagram or should i use three of them?
PMiczek, i am not sure of which current to add for the relays, but i have one old heatsink, ill be using it, anyway thank you.
in fact i am using three relays at the same time, and i think each one needs 10 mA as "detection current", i guess it is quite low in fact,
the datasheet of the relays can be found here
NAIS DS2E-S-DC12V http://www.soyter.cz/pdf/nais/DS_E.PDF
thanks Mikael, i did the layout myself from a stereo preamp pcb, just adjusting the different spaces to fit my components, you can find the pcb from beginning in my site under "protocircuit.jpg" to see the change,
bye
fred
Bas, for the diagram, it looks familiar to me now, thanks
concerning the caps, should i use one 2.2microF 25V, like on the diagram or should i use three of them?
PMiczek, i am not sure of which current to add for the relays, but i have one old heatsink, ill be using it, anyway thank you.
in fact i am using three relays at the same time, and i think each one needs 10 mA as "detection current", i guess it is quite low in fact,
the datasheet of the relays can be found here
NAIS DS2E-S-DC12V http://www.soyter.cz/pdf/nais/DS_E.PDF
thanks Mikael, i did the layout myself from a stereo preamp pcb, just adjusting the different spaces to fit my components, you can find the pcb from beginning in my site under "protocircuit.jpg" to see the change,
bye
fred
This looks like a very good relay, gold and silver contact, low power coil (200mW). You could probably drive about 12-15 of these with a 1A 12V regulator and this transformer before you need a heatsink, but I find that if you have room for it, using heatsinks in d-i-y is always a good thing. Plan on 16-20mA per relay, because they will draw more than the minimum "detection" of "pick-up" current when on.
The amount of capacitance will determine how much ripple is on the unregulated side of the supply (this is the input of the 12V reg.) For the low power you probably need (assuming 3-4 relay coils at 200mW each), one 2200uF (2.2mF) cap is sufficient, although I tend to be conservative with 60/120Hz noise, so I would put two anyway, you can use cheap caps here, and add a small ceramic cap, or even better a metal film cap if you have one lying around. This will help reduce the higher frequency spikes which you can get with some rectifiers. (Your relays will not care about the noise, but your audio circuit might).
You may also need at least a small cap on the output of the regulator, and depending on what you use to drive the relays, a small diode across the coil of the relay, also to reduce spikes when the relay opens.
(It all depends on how conservative you want to be with heat, noise and filtering, and ground connections... )
PM
The amount of capacitance will determine how much ripple is on the unregulated side of the supply (this is the input of the 12V reg.) For the low power you probably need (assuming 3-4 relay coils at 200mW each), one 2200uF (2.2mF) cap is sufficient, although I tend to be conservative with 60/120Hz noise, so I would put two anyway, you can use cheap caps here, and add a small ceramic cap, or even better a metal film cap if you have one lying around. This will help reduce the higher frequency spikes which you can get with some rectifiers. (Your relays will not care about the noise, but your audio circuit might).
You may also need at least a small cap on the output of the regulator, and depending on what you use to drive the relays, a small diode across the coil of the relay, also to reduce spikes when the relay opens.
(It all depends on how conservative you want to be with heat, noise and filtering, and ground connections... )
PM
My experience and use...
Hi,
I find a 9 volt winding is best. Bridge rectified and loaded it gives about 11 volts. (Almost) perfect for 12 volt relays.
If however, I'm passing low level signals through the relays, I'm careful that noise is filtered from the supply. Noise can intrude by coupling within the relay, and by PCB traces running parallel.
I wouldn't go so far as regulating the supply specially.
NB Relays fed with inadequately smoothed DC sometimes emit a buzzing noise.
Cheers,
Hi,
I find a 9 volt winding is best. Bridge rectified and loaded it gives about 11 volts. (Almost) perfect for 12 volt relays.
If however, I'm passing low level signals through the relays, I'm careful that noise is filtered from the supply. Noise can intrude by coupling within the relay, and by PCB traces running parallel.
I wouldn't go so far as regulating the supply specially.
NB Relays fed with inadequately smoothed DC sometimes emit a buzzing noise.
Cheers,
I did not mean to suggest that a relay coil REQUIRES a regulated 12V supply, obviously, at a semi-regulated 18-20 volts you would not exceed the relay coil rating.
Your ears might like it better if you do not run a couple volts of 120Hz ripple with diode switching noise on the same circuit board as switched audio signals.
With any luck that will not happen, but a 7800-series regulator and a couple caps seems cheap enough compared to the effort that goes into a typical home audio project.
Your ears might like it better if you do not run a couple volts of 120Hz ripple with diode switching noise on the same circuit board as switched audio signals.
With any luck that will not happen, but a 7800-series regulator and a couple caps seems cheap enough compared to the effort that goes into a typical home audio project.
thanks for all your replys, i can see there are different ways to do this
i think i am going to follow PMiczek advice, i feel more confortable with it
so the scheme is:
bridge rectifier- 2*2.2mF cheap caps - 1 metal film cap - regulator with heatsink- cap - and one diode (1N4007) across the coil of each relay (even if i have three of them on at the same time)
my last questions would be to know how much capacitance for the metal film cap and also for the cap after the regulator, i guess at least 2.2mF for the last one but for the metal film cap i am not sure
after this, i think everything will be ok and one more time, i wish to thank all of you for your help
bye
fred
i think i am going to follow PMiczek advice, i feel more confortable with it
so the scheme is:
bridge rectifier- 2*2.2mF cheap caps - 1 metal film cap - regulator with heatsink- cap - and one diode (1N4007) across the coil of each relay (even if i have three of them on at the same time)
my last questions would be to know how much capacitance for the metal film cap and also for the cap after the regulator, i guess at least 2.2mF for the last one but for the metal film cap i am not sure
after this, i think everything will be ok and one more time, i wish to thank all of you for your help
bye
fred
cap size
metal film cap: anything between 0.1 and 0.47uF will be fine
output: between 100uF and 2200uF
(I think you do not need a lot for a relay board, just so when the relays turn on, the inrush does not make a spike)
Again, this is pretty standard for a 12V linear supply, and quite conservative for your use. If you like I can send you a circuit diagram this weekend, but I don't have time to find one right now.
metal film cap: anything between 0.1 and 0.47uF will be fine
output: between 100uF and 2200uF
(I think you do not need a lot for a relay board, just so when the relays turn on, the inrush does not make a spike)
Again, this is pretty standard for a 12V linear supply, and quite conservative for your use. If you like I can send you a circuit diagram this weekend, but I don't have time to find one right now.
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