Need assistance with designing a Single input 120VAC and dual output DC converter

Status
Not open for further replies.
S

Sarray

Member
Location
Canada
Hi all,

I am trying to reduce the number of converters and wires for a project which will eventually be mass produced. Typically our lighting supplies require 12vDc Class 2 transformers or drivers both hardwired and plug in system.

I also have some phone chargers, ipad chargers that require 5vDC Chargers 3A.

For the prototype I used a single 12v DC supply has its own outputs and used the same supply to power a 5v buck converter. The 12v lights and the ipad chargers both function properly, my question is what other factors do I need to take in account such as a diode?

Should I consider using a diode in between the 12v DC supply and the buck converter? to restrict the return because I am using two different power sources and the second power sources is fully dependent on the first one.

In the event that someone over loads them, am I risking the ipads?

Thank you,
 
gar said:
180210-2008 EST

Sarray:

You need a much clearer statement of your problem, loads, goals, and why?

.
Click to expand...


Goal is to reduce the number of AC-DC Converters, plugs and cords. If I have 2 ipads and one low voltage lighting load on shelf I would need 2 converters (ipad chargers) and one low voltage LED driver.

This leaves me with the need to have 3 plugs.

If I choose one 12v Driver rated for 12v, 5A, 60 Watts and my LED Load is only 20 Watts. I have remaining 40 Watts that I can use elsewhere.

Using a buck converter rated for 5v, 30 Watts I can power 2 ipads. I want to use a 12v output from a driver and use that as an input for the buck.

Contain the transformer and the buck converter in one enclosure so I have one plug with dual 12v, 5v outputs

Main Power source
Input: 120VAC
Output:12v, 5A, 60 Watts

Load 1,
12vDC, 1 8Watts

Load 2
5vDC, 30 Watts

Thanks
 
Need assistance with designing a Single input 120VAC and dual output DC converter

Not sure of the commercial aspects of what you're trying to achieve, but you can buy what you're describing at retail for about $20. Combo 5/12 VDC switching power supplies are used in virtually every desktop computer produced in the last 20 years.
 
retirede said:
Not sure of the commercial aspects of what you're trying to achieve, but you can buy what you're describing at retail for about $20. Combo 5/12 VDC switching power supplies are used in virtually every desktop computer produced in the last 20 years.
Click to expand...

Hi,

Correct, they are many power supplies available however there aren't any Class -2 c(UL)US Listed power supplies that can perform both functions. In addition, Class 2 restricts the wattage to 60 Watts.

To comply with the code for the part of industry these will be used for, I would like to use one Class to supply and power another cUL Listed buck converter using the DC output jack of the first one.

However, if there is a supply CLASS 2 power supply which can provide 12v & 5v and carries a UL Mark it would be great..
 
180213-2125 EST

Sarray:

You have a Class 2 12 V DC power supply rated at 60 W maximum. You call it a driver and that really does not define what the driver is very well.

I will assume it is a regulated voltage DC supply with a current limiter function at 5 A. This would mean a constant DC output voltage of 12 V up until the load current reaches 5 A, then it goes plop to 0 V for any load greater than 5 A. It may not precisely do this, but likely this is an approximation.

You indicate a 20 W lamp load at 12 V DC. This is 1.7 A. Thus, you can put up to 3.3 A of additional load on the supply.

Almost any failure of your lamp load will produce an output voltage between 0 and 12 V. Thus, any switching regulator connected to this 12 V source will do whatever it does with inputs from 0 to 12 V. No need for diodes between your driver and the switching power supply(s).

I have no knowledge about iPads. This means I don't know if all battery charging control is done within the iPad.

If battery charging is totally controlled within the iPad, then just any 5 V DC source as input should be OK.

On-line iPad power supplies are listed at 10 and 12 W. This would imply 2 or 2.4 A at 5 V. At 100% efficiency this is 0.83 or 1.00 A at 12 V.

If current limiting is not required into the iPad, then your switching regulators don't require this function.

.
 
gar said:
180213-2125 EST

Sarray:

You have a Class 2 12 V DC power supply rated at 60 W maximum. You call it a driver and that really does not define what the driver is very well.

I will assume it is a regulated voltage DC supply with a current limiter function at 5 A. This would mean a constant DC output voltage of 12 V up until the load current reaches 5 A, then it goes plop to 0 V for any load greater than 5 A. It may not precisely do this, but likely this is an approximation.

You indicate a 20 W lamp load at 12 V DC. This is 1.7 A. Thus, you can put up to 3.3 A of additional load on the supply.

Almost any failure of your lamp load will produce an output voltage between 0 and 12 V. Thus, any switching regulator connected to this 12 V source will do whatever it does with inputs from 0 to 12 V. No need for diodes between your driver and the switching power supply(s).

I have no knowledge about iPads. This means I don't know if all battery charging control is done within the iPad.

If battery charging is totally controlled within the iPad, then just any 5 V DC source as input should be OK.

On-line iPad power supplies are listed at 10 and 12 W. This would imply 2 or 2.4 A at 5 V. At 100% efficiency this is 0.83 or 1.00 A at 12 V.

If current limiting is not required into the iPad, then your switching regulators don't require this function.

.
Click to expand...

Thank you so much for the description response.

The Class 2 transformer is rated at 12v, 5A 60 Watts. I was a little worried about the protection side of things incase the transformer gets overloaded.

For example if I have an ipad connected to it drawing 12 Watts I have 4 A left to use for the rest of the 12v load and if accidently someone overloads the transformer and connects a load that draws over 4.5 Amps, it will reduce the amount of current going to the ipad

ipads do have an internal current limiter and are rated for 5v 2.4Amps. I know that if less than the required current is supplied to ipads, iPhones etc it damages the device therefore I want to ensure that I am either providing 2.4Amps to the ipad or 0 nothing in between and possibly protect the direction of current if needed.
 
Using a buck converter rated for 5v, 30 Watts I can power 2 ipads. I want to use a 12v output from a driver and use that as an input for the buck.
Click to expand...

Buck converter?? Most 12v to 5v USB "chargers" are a simple 5v regulator IC. If your 12v supply should dip that is one of the reasons for the regulator, it should still provide 5v with an input well below 12v. If you are that concerned about supplying an iPhone with less than 5v someone can design a supply that will cut off during an under voltage condition. But that's not something that you are going to buy off the shelf.

If you were able to obtain the design of a Apple iPhone 120VAC charger you will see that there is a lot more going on than simply providing 5vdc. This is why aftermarket chargers or connecting to a USB port take forever to charge the phone- as will your scheme.

-Hal
 
180217-0952 EST

Sarray:

Since you are concerned about your iPads, then you need to find out more about the iPad.

What does the I-V curve look like from 0 to say 6 V for a fully charged, and near fully discharged iPad. From this you can probably determine whether you need protection from abnormal voltage in this range, or back-current feed.

For protection from higher voltages you may need a fuse, and something like a Transorb. A Transorb is a commercial product that is a specialized Zener diode designed and specified for transient voltage limiting.

If you can't find authentic information on the iPad and don't want to experiment over a wide voltage range, then test over 4.5 to 5.5 V. Depending upon what this tells you design a circuit that opens the circuit to the iPan for any voltage outside what you determine to be an acceptable range.

.
 
gar said:
What does the I-V curve look like from 0 to say 6 V for a fully charged, and near fully discharged iPad.
Click to expand...

Well, maybe but maybe not.

I'm sure the charging operation of the Apple charger and the phone itself is proprietary. I suspect information is exchanged between the phone and charger to provide a fast controlled charging (ie highest current vs temperature vs time). About the only given is that you can charge the phone via a USB cable from a 5vdc source, but even if the source can provide current equal to the Apple charger, the phone won't use it resulting in a much slower charge time.

I also don't believe that the phone can be damaged by an under voltage.

-Hal
 
Status
Not open for further replies.
Top