About the DC power supply charger

Thread Starter

LAOADAM

Joined Nov 21, 2018
273
Hi,
I measured few of the primary coil of DC power supply chargers, none of them conduct, this is against my cognition,
In my knowledge, the primary coil even the secondary coil should conduct and got a resistance reading, am I right?
Thanks
Adam
charger1.jpgcharger2.jpg
 

shortbus

Joined Sep 30, 2009
7,857
No. Those are switching power supplies. There are rectifiers before it ever gets to a transformer any other coil/inductor of any type. A transformer or linear power supply would have the primary coil your thinking of.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
273
No. Those are switching power supplies. There are rectifiers before it ever gets to a transformer any other coil/inductor of any type. A transformer or linear power supply would have the primary coil your thinking of.
Thanks.
The thing is some normal power supplies' (non switching power supplies) primary coil doesn't conduct neither. I even opened them and saw the primary coil direct connect to the plug.
Best
 

Tonyr1084

Joined Sep 24, 2015
4,927
Thanks.
The thing is some normal power supplies' (non switching power supplies) primary coil doesn't conduct neither. I even opened them and saw the primary coil direct connect to the plug.
Best
Show us a picture of what you're talking about please. I've opened many of those SMPS's (Switch Mode Power Supply) and have seen transformers in there. It may be possible you're seeing something and mis-interpreting it. It's also possible that some of the transformer coils you've measured were somehow open circuited. Dual primary can be configured by a PCB for 120 or 240 VAC. If there's a jumper between the two center leads it's probably for 240 VAC. If each lead marked with a • is joined together and the other two leads are joined together then it's a 120 VAC transformer (primary side). Secondary sides can also be individually wound coils. A center tapped transformer (secondary side) will only have three wires. And there are many many more transformer configurations out there. Ask and I will post a schematic diagram of a transformer I took out of a stereo. You'd be surprised at the number of different voltages that can be obtained by different sets of secondary coils.
 

MisterBill2

Joined Jan 23, 2018
6,779
Hi,
I measured few of the primary coil of DC power supply chargers, none of them conduct, this is against my cognition,
In my knowledge, the primary coil even the secondary coil should conduct and got a resistance reading, am I right?
Thanks
Adam
View attachment 214523View attachment 214524
Your knowledge is correct, but the devices shown have neither primary coils nor secondary coils because they are switching-mode power supplies. Their functioning is fundamentally different.
 
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