My question may sound dumb but I really have been looking and cannot find much on AC power supplies, either kits to build or ready built items for my audio amp that requires 12 Volts 2 amp AC current. There are plenty of materials for DC output units and some adapters for AC output but these are invariably in the 500MA output range and insufficient for my application.
Can some kind soul please point a newbie in the right direction? I will build one if I can finds some schematics or even buy a ready made to get my amp going.
Our mains current is 230VAC 60 cycles.
Thanks
Nico
Can some kind soul please point a newbie in the right direction? I will build one if I can finds some schematics or even buy a ready made to get my amp going.
Our mains current is 230VAC 60 cycles.
Thanks
Nico
It would help to know a bit more about the amp you want to power because ultimately all amps will require the supply to be DC.
If you really do need just 12 volts AC at 2 amp capability then you are looking at a single transformer of appropriate rating.
I somehow don't think that is what you mean though
If you really do need just 12 volts AC at 2 amp capability then you are looking at a single transformer of appropriate rating.
I somehow don't think that is what you mean though
Thanks.
Follow the link below to the item I have in mind.
Hope the information is sufficient.
Nico
NE5532 OP-AMP HIFI Amplifier Preamplifier Volume Tone Control Board Sale - Banggood.com
Follow the link below to the item I have in mind.
Hope the information is sufficient.
Nico
NE5532 OP-AMP HIFI Amplifier Preamplifier Volume Tone Control Board Sale - Banggood.com
Hi
With 2 NE5532 the current consumption would be max 30mA DC, and from the photos on the page you referred to, the power input states "AC-GND-AC", so what you are looking for is a transformer with the rating 12-0-12VAC, app 100mA or minimum 2VA (not A) should do the trick. The 2A you referred to is the VA (Volt Ampere) wich translates to 2VA/(12VAC+12VAC) = 83mA. Usually this means a small PCB mounted transformer.
On the face of it, 12VAC is a bit on low side (12V * 1,41 = 17V, a bit low for the LM7815 and LM7915), but these tiny transformers have a much higher output voltage when not loaded, around 15-16 V would be my guess. In this case the current consumption is quite low (20-30mA) so there should be no problem.
Lars
With 2 NE5532 the current consumption would be max 30mA DC, and from the photos on the page you referred to, the power input states "AC-GND-AC", so what you are looking for is a transformer with the rating 12-0-12VAC, app 100mA or minimum 2VA (not A) should do the trick. The 2A you referred to is the VA (Volt Ampere) wich translates to 2VA/(12VAC+12VAC) = 83mA. Usually this means a small PCB mounted transformer.
On the face of it, 12VAC is a bit on low side (12V * 1,41 = 17V, a bit low for the LM7815 and LM7915), but these tiny transformers have a much higher output voltage when not loaded, around 15-16 V would be my guess. In this case the current consumption is quite low (20-30mA) so there should be no problem.
Lars
You need a mains transformer.
12Vac is a bit low, but should work. I'd prefer to use a 15Vac transformer to feed 15V regulators.
Now the details.
you need either a centre tapped transformer 230:12-0-12vac of about 5VA or higher.
Or you can use a dual secondary 230:0-12, 0-12Vac again >=5VA - And convert this to centre tapped.
A 5VA transformer has a maximum continous output current of 5/(12+12) = 208mAac
When fed into a capacitor input filter you must de-rate that to ~ half ending up with ~ 110mAdc This will make the transformer run hot.
To operate cooler I suggest your maximum continuous DC current be limited to ~ 50% of that maximum, i.e. 55mAdc and that is plenty to operate that tone control circuit.
A typical quiescent current for the 5532 is 8mA total for both channels, but the maximum is specified as 16mA. Each regulator could take another 5mA back to the centre tap.
Two 5532 could theoretically draw 32mA (+5mA for reg.) of quiescent current continuously. In addition any output current has to be added to that, but this addition is not continuous. So the 55mA from the 5VA is sufficient.
BTW,
a 15-0-15Vac 5VA has a maximum continuosu AC current of 166mAac and I recommend a maximum continuous DC current after the capacitor input filter of 42mAdc. Note this still exceeds the absolute max of 37mA quiescent for the two 5532+regs.
DO NOT use a 2VA transformer !!!!!!!!
12Vac is a bit low, but should work. I'd prefer to use a 15Vac transformer to feed 15V regulators.
Now the details.
you need either a centre tapped transformer 230:12-0-12vac of about 5VA or higher.
Or you can use a dual secondary 230:0-12, 0-12Vac again >=5VA - And convert this to centre tapped.
A 5VA transformer has a maximum continous output current of 5/(12+12) = 208mAac
When fed into a capacitor input filter you must de-rate that to ~ half ending up with ~ 110mAdc This will make the transformer run hot.
To operate cooler I suggest your maximum continuous DC current be limited to ~ 50% of that maximum, i.e. 55mAdc and that is plenty to operate that tone control circuit.
A typical quiescent current for the 5532 is 8mA total for both channels, but the maximum is specified as 16mA. Each regulator could take another 5mA back to the centre tap.
Two 5532 could theoretically draw 32mA (+5mA for reg.) of quiescent current continuously. In addition any output current has to be added to that, but this addition is not continuous. So the 55mA from the 5VA is sufficient.
BTW,
a 15-0-15Vac 5VA has a maximum continuosu AC current of 166mAac and I recommend a maximum continuous DC current after the capacitor input filter of 42mAdc. Note this still exceeds the absolute max of 37mA quiescent for the two 5532+regs.
DO NOT use a 2VA transformer !!!!!!!!
Last edited:
Thanks for the inputs.
I have a number of small PCB transformers scavenged from old crt monitors, pc main boards etc and will look at what I have there first but perhaps purchasing a new one with the correct pecs might be more prudent.
Since I am a little confused, not having any electronic experience or knowledge perhaps someone could write me the specs I should search for in sourcing attempts. We have a local RS Components where I usually get what I need - if I know what to specify.
Thanks again.
Nico
I have a number of small PCB transformers scavenged from old crt monitors, pc main boards etc and will look at what I have there first but perhaps purchasing a new one with the correct pecs might be more prudent.
Since I am a little confused, not having any electronic experience or knowledge perhaps someone could write me the specs I should search for in sourcing attempts. We have a local RS Components where I usually get what I need - if I know what to specify.
Thanks again.
Nico
Here are the ones I have found. The prices are similar with the toiroidal slightly more expensive but quite affordable. I tend to lean towards the toiroidal 15VAC but advice will be welcome if these are indeed the right ones...
Toiroidal transformers
12VAC
Primary Voltage Rating
115V ac, 230V ac
Secondary Voltage Rating
2 x 12V ac
Power Rating
5VA
Number of Outputs
2
Secondary Current
208mA
Weight
144g
Dimensions
49.7 x 49.7 x 19.5mm
Minimum Operating Frequency
50Hz
Maximum Operating Frequency
60Hz
Mounting Type
PCB
Termination Type
Pin
Fixing Hole Diameter
M4
Maximum Temperature
+60°C
15VAC
Primary Voltage Rating
115V ac, 230V ac
Secondary Voltage Rating
2 x 15V ac
Power Rating
5VA
Number of Outputs
2
Secondary Current
167mA
Weight
144g
Dimensions
49.7 x 49.7 x 19.5mm
Minimum Operating Frequency
50Hz
Maximum Operating Frequency
60Hz
Mounting Type
PCB
Termination Type
Pin
Fixing Hole Diameter
M4
Maximum Temperature
+60°C
Mains transformers
15VAC
Secondary Voltage Rating
15V ac
Power Rating
5VA
Primary Voltage Rating
230V ac
Number of Outputs
2
Length
44mm
Width
33mm
Depth
37mm
Dimensions
44 x 33 x 37mm
Weight
190g
Mounting Type
Through Hole
Maximum Temperature
+50°C
12VAC
Secondary Voltage Rating
12V ac
Power Rating
5VA
Primary Voltage Rating
230V ac
Number of Outputs
2
Length
44.25mm
Depth
32.25mm
Dimensions
44.25 x 37 x 32.25mm
Weight
200g
Mounting Type
Through Hole
Maximum Temperature
+50°C
Minimum Operating Frequency
50Hz
Maximum Operating Frequency
60Hz
Nico
Toiroidal transformers
12VAC
Primary Voltage Rating
115V ac, 230V ac
Secondary Voltage Rating
2 x 12V ac
Power Rating
5VA
Number of Outputs
2
Secondary Current
208mA
Weight
144g
Dimensions
49.7 x 49.7 x 19.5mm
Minimum Operating Frequency
50Hz
Maximum Operating Frequency
60Hz
Mounting Type
PCB
Termination Type
Pin
Fixing Hole Diameter
M4
Maximum Temperature
+60°C
15VAC
Primary Voltage Rating
115V ac, 230V ac
Secondary Voltage Rating
2 x 15V ac
Power Rating
5VA
Number of Outputs
2
Secondary Current
167mA
Weight
144g
Dimensions
49.7 x 49.7 x 19.5mm
Minimum Operating Frequency
50Hz
Maximum Operating Frequency
60Hz
Mounting Type
PCB
Termination Type
Pin
Fixing Hole Diameter
M4
Maximum Temperature
+60°C
Mains transformers
15VAC
Secondary Voltage Rating
15V ac
Power Rating
5VA
Primary Voltage Rating
230V ac
Number of Outputs
2
Length
44mm
Width
33mm
Depth
37mm
Dimensions
44 x 33 x 37mm
Weight
190g
Mounting Type
Through Hole
Maximum Temperature
+50°C
12VAC
Secondary Voltage Rating
12V ac
Power Rating
5VA
Primary Voltage Rating
230V ac
Number of Outputs
2
Length
44.25mm
Depth
32.25mm
Dimensions
44.25 x 37 x 32.25mm
Weight
200g
Mounting Type
Through Hole
Maximum Temperature
+50°C
Minimum Operating Frequency
50Hz
Maximum Operating Frequency
60Hz
Nico
Order one of these. Whack the end off and connect to two of the power connections. (Center and to either of the other two) Ya can't hook it up wrong..
US EU 100-240V Converter Adapter 12V 2A Power Supply For LED Strip - US$4.21
US EU 100-240V Converter Adapter 12V 2A Power Supply For LED Strip - US$4.21
I believe the OP wanted a 12V AC output on the secondaries. Not a 110/230V AC to 12V DC converter (your model above states clearly that it is an AC to DC adaptor).
Best,
Anand.
I have already built a mains bulb tester and intend to use it - often.
Thanks to everyone who responded to my question. However, I have not a direct reply regarding the transformer I need to get. In post #9 I have listed four possible model which to me appear to be either close to or ideal for my purpose. The most expensive toiroidal is around $16 and I don't mind paying that for the best one.
Could someone please comment on my post #9? Thanks.
Nico
Thanks to everyone who responded to my question. However, I have not a direct reply regarding the transformer I need to get. In post #9 I have listed four possible model which to me appear to be either close to or ideal for my purpose. The most expensive toiroidal is around $16 and I don't mind paying that for the best one.
Could someone please comment on my post #9? Thanks.
Nico
They are virtually the same. All are 5VA, all are 230Vac
Choose one.
If cost is not an issue I would suggest you buy one 12Vac and one 15Vac. then test the actual DC voltage when under load.
The regulation of these very small transformers is very high and leads to very high DC voltages when the loading is low.
You may find that the 15Vac is just too high a DC voltage and then you would fit the 12Vac to keep the regulators cooler.
Choose one.
If cost is not an issue I would suggest you buy one 12Vac and one 15Vac. then test the actual DC voltage when under load.
The regulation of these very small transformers is very high and leads to very high DC voltages when the loading is low.
You may find that the 15Vac is just too high a DC voltage and then you would fit the 12Vac to keep the regulators cooler.
My bad. I seen (what I thought was) a full wave bridge behind the power input and assumed a single D.C. supply would be sufficient. The other thing(s) I missed were the two 15 volt regulators. (7815 / 7915) Not enough coffee, I guess..
They suggest a 12Vac transformer with no mention for the need of a center tap.
They suggest a 12Vac transformer with no mention for the need of a center tap.
the PCB is labelled AC GND AC.
That means a 3 wire ac connection is required.
The gnd is mislabelled and should read CT for centre tap.
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