Switching Mode Power Supply Input Transformer Specification

Hi Gerald,

I'm not sure I have understood your questions.

1- In my understanding your maximum Input Power is 150W (15VDC x 10ADC).
Assuming 87% efficiency the Power Supply input power would be around 150W/Eff=172W.
So if you want to use a transformer to isolate your SMSP from main during testing:
Assuming Transformer efficiency around 80% and 0.9 Power factor your transformer input power in VA would be around (172 /0.8)/PF = 238VA
A would say around 250VA to have some margin.

2- I don't know what kind of doorbell transformer you have but probably answer would be no.
3- I really do not understand what you mean.

Please try to be more specific, I did not understand what you want to do.
If you already have an SMPS or if you have to design an SMPS.

As general information:
- for 150W SMPS generally a two stage SMSP is used.
- First stage, that is directly connected to line, is used to Power factor Correction.
Generally this stage provides the second stage input voltage the in the most of application is a 400V DC voltage
Check out Power Factor Correction web page:
www.ti.com/.../overview.html

As specific part number you ca use UCC28056 as controller .

- Second stage converts 400VDC bus to the desired output voltage providing also isolation.
generally for this purpose LLC converter are used I can suggest UCC256301


Best regards
Davide

Davide:  Thank you for the information on how to determine the required VA electrical size for the power transformer.  This information is exactly what I needed.  I am replacing the old NiCad batteries for my 12 volt Panasonic drill with a DC power supply.

Measured Full Load Current Draw - This turns out to be 30 amps.

Worse Case Load Resistance Used in PSpice Model - 12 Volts / 30 A  = 0.4 Ohm

Minimum Transformer Size - 12 Volts x 30 amps = 360 VA, bump this up to 450VA for design margin. 115 volt primary, 24 volt secondary.

It turns out that I have a "boat anchor" transformer lying around which I can use for this purpose.

 

Linear Power Supply with Pass Power Transistor - Since I will be using the drill and this power supply in my garage woodworking shop, I have decided to use a linear DC power supply of this type.  The two PSpice models attached, including related plots of current and voltages illustrate the performance of this type of supply. 

I will need to tweak the resistors on the Op Amp to get the load voltage closer to 12 volts, RMS, and the load current closer to 30 amps RMS.  I will likely replace the three TIP102, NPN power Darlington transistors with one capable of continuously driving 40 amps or more of collector current into the drill motor.

Comments Invited - Any comments from you are invited.

By the way, I did want to tell you that I am a retired RF/Microwave engineer with a 40-year Modeled Transistor Linear Power Supply, Using Ideal Op Amp and Three TIP 102 Transistors.docxModeled Transistor Linear Power Supply, Using LM324 Op Amp and Three TIP 102 Transistors.docxcareer working and designing circuits in the frequency range from 100 KHz, up to 100 GHz.  However, power electronics has always been one of my interests.

Panasonic displayed all of the interest modeled by a cold brick working the dead, 12 volt NiCad battery issue, replacing same with Lithium Ion equivalents.  That's when I decided to design my own DC power supply replacement for same.

 

My apologies for taking this long to get back with you, but using your initial comments to me, I had a lot of learning and modeling to do.

 

Best wishes,

Jerry Renken, PE