Why AC/DC PSU won't work when supplied with DC?

Thread Starter

Dods

Joined Jun 11, 2019
7
Hi,

I'm using TOP60124 https://assets.tracopower.com/20190701131007/TOP60/documents/top60-datasheet.pdf
When I supply it with DC, it works but only when connected in one way.
When I switch the wires, it doesn't work.
Anyone has any idea why it would behave like that?
Shouldn't it work both ways? I mean, it is a AC/DC PSU, it shouldn't care about polarity on iput?

Also, what can i add to the input so that i could "fix" the issue?
 

ericgibbs

Joined Jan 29, 2010
8,737
hi,
Depending upon the internal switching circuitry there maybe a series diode on one of the 'AC' which prevents the DC input from being connected in either direction.
I would recommend that you do not try to bypass any input protection.

Is there a reason that you need the option to connect a DC input either way around.?
E
 

LesJones

Joined Jan 8, 2017
2,323
Either one or two of the diodes in the input bridge rectifier are open circuit or the power supply uses half wave rectification on the input. Trace out the input rectification part of the schematic. Adding a bridge rectifier between the DC input and the power supply input would solve the problem by ensuring the polarity at the PSU input was the same irrespective of the polarity to the bridge.

Les.
 
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Thread Starter

Dods

Joined Jun 11, 2019
7
Thank you both for the answers.
I don't want to bypass any protections, just trying to make it work.
Half-wave rectifier makes sense, but i didn't think they would put it, seems kinda "old".
I was thinking maybe some PFC inside has to do with it, since DC never goes to 0, but that are all guesses.

Is there a reason that you need the option to connect a DC input either way around.?
E
Yes, because it should work no matter how it is connected, because input may vary from AC to DC while in operation. If it shuts off when DC input comes, my device stops working :D

Either one or two of the diodes in the input bridge rectifier are open circuit or the power supply uses half wave rectification on the input. Trace out the input rectification part of the schematic. Adding a bridge rectifier between the DC input and the power supply input would solve the problem by ensuring the polarity at the PSU input was the same irrespective of the polarity to the bridge.

Les.
PSU is brand new, so there shouldn't be any diodes open :/
Looks like i'll have to add the BR before the supply anyways, i was hoping i was missing something, but seems like that would be the only solution.
Still waiting for manufacturers reply, if it comes, i'll share.
 

Thread Starter

Dods

Joined Jun 11, 2019
7
If you trace out the schematic and post it someone will be able to work out an explanation.

Les.
Sorry, but i'm really not in the mood for tracing out the PSU, i was just hoping maybe someone faced a simmilar issue before me.
 

Thread Starter

Dods

Joined Jun 11, 2019
7
hi,
Depending upon the internal switching circuitry there maybe a series diode on one of the 'AC' which prevents the DC input from being connected in either direction.
I would recommend that you do not try to bypass any input protection.

Is there a reason that you need the option to connect a DC input either way around.?
E
Got info from the manufacturer, seems like there's some startup circuit in front of the bridge, that's why it doesn't work.
The more you know...
 

MisterBill2

Joined Jan 23, 2018
3,883
There is no reason to expect an AC/DC device to work with both polarities of DC. Only heating devices would probably work, any other kind of device would work with one polarity but not the opposite. So just mark the plug so you know which way works.
 
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