If a uC requires an isolated DC power supply, can that be done without a transformer? It would be, obviously, a very low-power supply.

Could power be delivered with an optoisolator?

 

Most optoisolators use photo transistors which can only control current and do not supply power. Similarly some might use a photocell which is a light-variable resistor. My first reaction to your request was to say "impossible" but when you mentioned optoisolator, my response is "small solar panel." However, transformers need not be a big deal and might be easier to implement with small driver circuit rather than using a solar panel and means of regulating its output. Transformer can be much more efficient than a lamp powering a solar panel. Will your uC have sunlight available or do you need to operate without sunlight?

 

If a uC requires an isolated DC power supply, can that be done without a transformer? It would be, obviously, a very low-power supply.

No, you need a transformer to transfer power with isolation.

Could power be delivered with an optoisolator?

No
Integrated opto-isolators transmit signals with isolation but require isolated power on the output for that.
The exception is one type that uses a small photo cell to generate a very low current signal (a few tens of microamps) to drive a MOSFET gate, which would not be enough to power a µC.

You could conceivable make one with a high power light source shining on a solar cell, but it would not be very efficient (perhaps 10% at best).
How much power would you need?

 

Will your uC have sunlight available or do you need to operate without sunlight?

No sunlight, and it needs to be rather small and cheap (under $1 for all parts). It's driving a couple of low-power parts, eg a uC and op amp.

 

it needs to be rather small and cheap (under $1 for all parts)

The cheapest would likely be a small switching supply, either flyback or switched inductor.
It operates at a high frequency so the transformer/inductor can be quite small.

What is the source of the power you need to isolate?

 

What is the source of the power you need to isolate?

Regulated DC from a typical laptop wall charger.

 

Regulated DC from a typical laptop wall charger.

That's already isolated from the mains.
Why do you need further isolation?

 

That's already isolated from the mains.
Why do you need further isolation?

This isn't for isolation from mains, it's for isolation from other parts of the circuit. Take my word for it.

 

This isn't for isolation from mains, it's for isolation from other parts of the circuit. Take my word for it.

Since you seem to have only a rudimentary knowledge of electronics, I don't think I will.
Unless you can show why you need isolation, I won't spend further effort on a solution.

 

Since you seem to have only a rudimentary knowledge of electronics, I don't think I will.
Unless you can show why you need isolation, I won't spend further effort on a solution.

That's your choice, but i think the appropriate thing here is to focus on the question that i posted, without concerning yourself with externalities. This is a "how" post, not a "why" post.

 

That's your choice, but i think the appropriate thing here is to focus on the question that i posted, without concerning yourself with externalities. This is a "how" post, not a "why" post.

This attitude is why your threads never seem to get to a resilution.

But I’ll play. High powered LEDs focused on a solar panel. Not very efficient, but definitely isolated.

 

This attitude is why your threads never seem to get to a resilution.

But I’ll play. High powered LEDs focused on a solar panel. Not very efficient, but definitely isolated.

Most of my threads do get a resolution. It's unclear why factors external to my question are of concern here. I'm not asking if i need an isolated supply, only asking how to do it. It's disrespectful for someone to question whether i should do what i'm asking. I'm not asking if i "should". It's also disrespectful for someone to insult me. For someone in this forum to say "I'm not going to answer your question because you're ignorant" is inappropriate. I'm not the person bringing drama here. Let's stay on topic -- electronics.

 

High powered LEDs focused on a solar panel. Not very efficient, but definitely isolated.

Getting back to the actual substance of this post:
Your solution is interesting. This needs to be small. I wonder if there's an off-the-shelf component which is solar material and LED inside a small component.

Maybe a linear optoisolator?

This doesn't have to be all that efficient, because it's running off mains.

 

Getting back to the actual substance of this post:
Your solution is interesting. This There are, but theneeds to be small. I wonder if there's an off-the-shelf component which is solar material and LED inside a small component. This doesn't have to be all that efficient, because it's running off mains.

There are. But probably not that produce enough power. I think they are called photovoltaic opto isolators. Intended to provide gate drive for a MOSFET or IGBT.

 

"I'm not going to answer your question because you're ignorant" is inappropriate.

And to diss my question is also inappropriate.
Many times posters want answers to what they think is needed to solve a problem when it's actually not a problem.
Thus I won't waste time trying to solve a possibly non-existent problem.

So carry on as if you know what your are doing.

 

Many times posters want answers to what they think is needed to solve a problem when it's actually not a problem.

I appreciate you trying to help me avoid going down a wrong path. In this case, I've been working on this project for a few years, and have consulted with some pro EE's, so i know that isolation is an essential element of the whole system. Have a good day.

 

Ok, so make a small transformer and drive with pulses from an NE555 or an MC34063 (the 34963 gves you regulation).

The lack of detail is not helping.

 

The lack of information is a real problem. We don't know exactly what voltage and current your application needs, but even more important, is this for intermittent or continuous use? I could probably make suggestions for both cases, but I would be wasting half of my time and effort in considering it.
I am not trying to be difficult. I am just trying to help. The suitability of suggested solutions depends directly on the amount of relevant information you can supply.

 

It's unclear why factors external to my question are of concern here.

In my career as an engineer, the problem is often getting past the "ask" to understand the "need". It comes down to understanding the problem.

Since you asked about a low voltage isolated power supply NOT using a transformer. The the obvious conclusion is you want to reduce AC line power to DC and you understand that some form of isolation is required for safety. So using a DC laptop charger is a totally unexpected turn. Presumably you need NOISE isolation?

 

"High powered LEDs focused on a solar panel. Not very efficient, but definitely isolated."

For that matter, and ahem the direction of this thread, you could use two DC motors with a coupled shaft and make your own dynamotor. It would at least be more efficient and you could probably source some pretty small motors. <smirk>