# Is there a way to check this SMPS transformer (schematic)?

#### Lumenosity

Joined Mar 1, 2017
636
Hello,

I am having a hard time determining whether this transformer is functioning properly or not.
It is in a 300watt Modified Sine Wave Inverter and receives 12v as shown in the schematic below.
Each pin on the transformer is numbered below. I'm not even sure which side is primary and which is secondary.

I have attempted to apply 12v DC voltage to the transformer removed from the circuit and the results were confusing.
I connected 12v + to pins 3 and 4 and 12v - to pins 5 and 6. What I got from pins 10 and 11 was AC 1v at varying frequency from 30Hz to 181Hz
This is not what I was expecting. I was expecting an higher DC voltage output.
When the VOM meter was set to DC I got absolutely nothing. No reading at all from pins 10 and 11.

I also have a DE-5000 inductance meter.
I got 3.376 mH across pins 10 and 11
28.9uH between 5/6 and 3/4
28.9uH between 1/2 and 3/4
116uH between 1/2 and 5/6

Any insight or guidance appreciated. I'm somewhat lost.
Thanks

And here is the schematic of it in circuit.....

Last edited:

#### Ian0

Joined Aug 7, 2020
3,784
It's a push-pull primary, with V+ connected to pins 3/4 (labelled 4 on your schematic) and the MOSFET drains connected to pins 1/2 and 5/6 (labelled 3 and 5 on your schematic)
The output is on pins 10/11 (labelled 1 and 2 on your schematic)

#### Lumenosity

Joined Mar 1, 2017
636
Any idea what the output on pins 10/11 should be ?

#### Ian0

Joined Aug 7, 2020
3,784
Any idea what the output on pins 10/11 should be ?
$$V_{sec}=V_{pri}\sqrt\frac{L_{sec}}{L_{pri}}$$

#### LesJones

Joined Jan 8, 2017
3,572
Lumenosity, As you seem to think a transformer will work with DC you need to read up on transformer theory. If you don't understand how they work you have no chance of understanding how circuits using them works.

Les.

#### Lumenosity

Joined Mar 1, 2017
636
Lumenosity, As you seem to think a transformer will work with DC you need to read up on transformer theory. If you don't understand how they work you have no chance of understanding how circuits using them works.

Les.
I understand. That simple statement has just changed my direction so thanks.
I have read quite a few articles on transformer theory and inductance etc.
I admit I must be a slow learner at this point (yes, I'm a senior citizen trying to learn electronics)
It gets VERY confusing.

https://www.haloelectronics.com/products/dc-dc-transformers/
HALO offers a full line of DC/DC transformers for PoE, PoE+, and high voltage isolation applications. Please contact the factory or your local representative for non-standard turns ratios or custom design requests.

The hope was that through help and from continued study the proverbial lightbulb will eventually come on.

#### Lumenosity

Joined Mar 1, 2017
636
Lumenosity, As you seem to think a transformer will work with DC you need to read up on transformer theory. If you don't understand how they work you have no chance of understanding how circuits using them works.

Les.
In the schematic I included, can you tell me how AC is fed to the transformer when it is connected to DC?
Are the MOSFETS there to created the AC current?
Thanks