AC/DC converter (110VAC to 12VDC, 120W)

Thread Starter

Warlockgoosy

Joined May 19, 2021
7
I'm looking to design a PCB that will have a 110VAC input and convert it to 24VDC output with a maximum load current of 5A.
Is mounting the step down transformer on the PCB a good idea?
What better ways are there to do it?
 

dcbingaman

Joined Jun 30, 2021
495

dcbingaman

Joined Jun 30, 2021
495

Thread Starter

Warlockgoosy

Joined May 19, 2021
7
Here is a module that will handle it all for you:

https://www.digikey.com/en/products/detail/delta-electronics/PACSR24012S/7322769

It is fairly expensive, does your project really need that much current?
I would at least need a maximum of 2A current to run an actuator that I will be connecting it to. I'm a little worried that it will become an issue in terms of space requirements to allocate all the filter components etc,. So, I'm looking for a simple yet efficient design that I can implement.
 

dcbingaman

Joined Jun 30, 2021
495
I would at least need a maximum of 2A current to run an actuator that I will be connecting it to. I'm a little worried that it will become an issue in terms of space requirements to allocate all the filter components etc,. So, I'm looking for a simple yet efficient design that I can implement.
Here is a very small compact unit that can put out 2.5A:
https://www.digikey.com/en/products/detail/mean-well-usa-inc/IRM-60-24/7704690

At less than 20 bucks and immediately available from digikey.

size: 3.43" L x 2.05" W x 1.16" H (87.0mm x 52.0mm x 29.5mm)
 

Ian0

Joined Aug 7, 2020
3,754
Is mounting the step down transformer on the PCB a good idea?
You'll probably be mounting the PCB on the transformer!
There aren't many 120VA PCB mounting transformers out there.
If you don't need a very accurate 24V and a bit of ripple won't do any harm, then you can use a very simple rectifier and capacitor circuit, which will be very reliable.
Reliability will probably determine whether you use a good-old-fashioned and completely reliable 50/60Hz transformer, or whether you buy a cheap switcher off Amazon.
Do you need 120VA (24V @ 5A) all the time? 50/60Hz transformers can be used at up to 3x their rated output for intermittent operation.
 

Thread Starter

Warlockgoosy

Joined May 19, 2021
7
You'll probably be mounting the PCB on the transformer!
There aren't many 120VA PCB mounting transformers out there.
If you don't need a very accurate 24V and a bit of ripple won't do any harm, then you can use a very simple rectifier and capacitor circuit, which will be very reliable.
Reliability will probably determine whether you use a good-old-fashioned and completely reliable 50/60Hz transformer, or whether you buy a cheap switcher off Amazon.
Do you need 120VA (24V @ 5A) all the time? 50/60Hz transformers can be used at up to 3x their rated output for intermittent operation.
I don't need 5A all the time, but whenever the load activated it needs 1.5A. Also, I'd like something less noisy (imagine as this needs to be in a commercial product).
 

Ian0

Joined Aug 7, 2020
3,754
The main question is now about the nature of the load. Does it need an accurate 24V, or would 24V±10% do? Can it withstand a couple of volts of ripple?
If so, 18V 40VA transformer, bridge rectifier and 6800uF smoothing capacitor will do. If the load is a motor or something else with an inrush current that takes it briefly to 5A, then it will be OK.
 

MrSalts

Joined Apr 2, 2020
712
I don't need 5A all the time, but whenever the load activated it needs 1.5A. Also, I'd like something less noisy (imagine as this needs to be in a commercial product).
For safety, you're much better off with a desktop power supply so the user is only seeing the 24vdc output from the brick to your device. Also, if it is a Consumer product, getting through the EMI hurdles will be somewhat easier and cheaper if you start with a pre-built power supply. If you need durability and low noise, look for one that is rated for medical applications on a reputable Distributor's website (not Amazon).

Also, are you after 24v (post 1) or 12V in title of this thread.
 

Ian0

Joined Aug 7, 2020
3,754
getting through the EMI hurdles will be somewhat easier and cheaper if you start with a pre-built power supply.
Only "somewhat" because a certificate for the power supply is no proof that the final product is compliant!
A transformer/rectifier/capacitor supply may make EMI compliance easier, but not if the final product is "lighting" as it might fail on harmonic currents.
Similarly, a fully certified power supply may be the cause of failure if the final product was lighting, and the power supply was not power-factor corrected.
 

MrSalts

Joined Apr 2, 2020
712
Only "somewhat" because a certificate for the power supply is no proof that the final product is compliant!
A transformer/rectifier/capacitor supply may make EMI compliance easier, but not if the final product is "lighting" as it might fail on harmonic currents.
Similarly, a fully certified power supply may be the cause of failure if the final product was lighting, and the power supply was not power-factor corrected.
Thank you for confirming what I said and I completely reject any additional assertions that imply my post was incorrect or incomplete.

Even if the product is "lightning", it would still be lightning if designed with an on-board PSU, right? So with an external power supply, the OP will know to look at his product, not the power supply.

In the very rare scenario that the PSU is "CAUSING" the EMI issues, it becomes infinitely easier to track down by simply testing a different PSU that operates at a different frequency, then analyzing the differences. This is way easier than redesigning an internal PSU - especially if it is on the same PCB as the device.

So, I don't really see any situation where an onboard PSU makes a project easier as your post tries to dispute my assertions.
 

Ian0

Joined Aug 7, 2020
3,754
The crux of the matter is the 5A/1.5A current spec. If it is 1.5A normally with a 5A inrush, then a transformer/rectifier/capacitor supply rated at 36W would do it, but a switched-mode would have to be rated at 120VA to deal with the inrush.
 

Thread Starter

Warlockgoosy

Joined May 19, 2021
7
The crux of the matter is the 5A/1.5A current spec. If it is 1.5A normally with a 5A inrush, then a transformer/rectifier/capacitor supply rated at 36W would do it, but a switched-mode would have to be rated at 120VA to deal with the inrush.
For safety, you're much better off with a desktop power supply so the user is only seeing the 24vdc output from the brick to your device. Also, if it is a Consumer product, getting through the EMI hurdles will be somewhat easier and cheaper if you start with a pre-built power supply. If you need durability and low noise, look for one that is rated for medical applications on a reputable Distributor's website (not Amazon).

Also, are you after 24v (post 1) or 12V in title of this thread.
[/QUOT
The main question is now about the nature of the load. Does it need an accurate 24V, or would 24V±10% do? Can it withstand a couple of volts of ripple?
If so, 18V 40VA transformer, bridge rectifier and 6800uF smoothing capacitor will do. If the load is a motor or something else with an inrush current that takes it briefly to 5A, then it will be OK.
I have worked on low power circuits and battery operated designs. This whole high voltage power electronics design (especially with EMI considerations is giving me a nightmare). I will be using a linear actuator or a solenoid( have not decided on whether to use a 24V or a 12V one). Are there any evaluation boards that I can test first before implementing in my own design.
 

Ian0

Joined Aug 7, 2020
3,754
Presumably the solenoid is responsible for the brief 5A pulses. Go for the simple, transformer/rectifier/capacitor supply. It will cope with the solenoid.
 

MrSalts

Joined Apr 2, 2020
712
The crux of the matter is the 5A/1.5A current spec. If it is 1.5A normally with a 5A inrush, then a transformer/rectifier/capacitor supply rated at 36W would do it, but a switched-mode would have to be rated at 120VA to deal with the inrush.
It all depends on how long the solenoid will be activated and how big the capacitors are.
A good, brand name power 120w supply in quantity will cost 35-40USD with power cord. A transformer alone will cost $15-20 (assuming a short pulse is only needed). Add a few more dollars for cord, more for capacitors, assembly, housing, labels, safety certification, ....
 
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