Unregulated, Isolated, Low-Parts Count?

Thread Starter

johnyradio

Joined Oct 26, 2012
278
Hi

Seeking a very low parts count (< 10 parts), unregulated, isolated, 10W DC/DC converter.
The only purpose of this circuit is to provide isolation, not regulation.

Input: 12V - 24V
Output: approx 4V - 9V, 2A
i'd like to do this with a switched-mode power supply, to minimize heat and size.

My reasons to reduce parts count are:
  • to reduce overall PCB footprint
  • simpler for the designer to build it

It happens that a divide-by-3 circuit would keep my output in desired range.
12V/3=4V
24V/3=8V.
The concern then is whether temperature or load could cause deviation outside my desired output-range.

Hoping for a short-height of all parts (especially inductor): < 5 mm. i can be more flexible on inductor footprint (length, width). So, a MHz clock rate would be preferred.

As always, cost is a consideration. Hoping to achieve this for about $5 total.

Any suggestions?

thx
 
Last edited:

Papabravo

Joined Feb 24, 2006
14,701
Good luck. How can you have the output remain at +5V Volts over that input range if it is unregulated? Or do you just not know what you are asking for?
 

Thread Starter

johnyradio

Joined Oct 26, 2012
278
i don't care if the voltage drifts, whether due to temperature, changes in source voltage, changes in load, or anything else. That's why "unregulated".
 

Papabravo

Joined Feb 24, 2006
14,701
It will take "some" kind of regulation to get the output to be "around" 5V over the entire input range. You just don't know anything about power conversion -- do you?
Stop wasting our time.
 

ronsimpson

Joined Oct 7, 2019
1,024
Less parts?
You need a transformer to get isolation. On the output: diode(s) and capacitor. (don't count the LC filter "optional")
Need a oscillator to make ac because transformers do not work with dc.
Need power transistor/MOSFET.
This circuit does not regulate in any way. It uses the transformer turn ratio to make a different voltage.
Circuit as shown 5V to 5V at 500mA. Could change the transformer to 12V to 5V at 1A. (you want 2A)
Input voltage must not get above 17V!
Does not meet your specifications. But less parts.
1600953774954.png
I have used this part. I think there is another one like this from TI or Onsemi but don't remember.
 

Papabravo

Joined Feb 24, 2006
14,701
It's always something, Certainly enough choices to require some homework and some decision making.
Why do I suspect that the TS still wants more?
 

Thread Starter

johnyradio

Joined Oct 26, 2012
278
@Papabravo your hostility and disrespect are inappropriate and unwanted. So far, you have contributed nothing of value to this conversation, only insults and personal criticisms. Why don't you make an effort to offer solutions?
 

Thread Starter

johnyradio

Joined Oct 26, 2012
278
Circuit as shown 5V to 5V at 500mA. Could change the transformer to 12V to 5V at 1A. (you want 2A)
Input voltage must not get above 17V!
Does not meet your specifications. But less parts.
View attachment 217892
I think there is another one like this from TI or Onsemi but don't remember.
Another fantastic answer from @ronsimpson ! Wow, 8 external parts.

I could relax the current requirement from 2A to 1A. But i can't restrict input V to 17V limit. Input could go as high as 24V, so unfortunately can't use this particular solution. But this might suggest other similar options. I'll check out Onsemi and TI. Thx!
 
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