Power question

Hello all,
Im trying to reverse engineer a circuit. Ultimately I want to reproduce it but with more options. However I have one simple question…

This circuit uses low & high voltage, however I don’t see a transformer!!! I am not an expert, but I assume that there is both Low & High voltage circuits… but where is the low voltage coming from???

Any insight would be helpful!

Thanks,

Bottom View

Turn it around to top view, there you will find a small High Frequency transformer. The circuit here is a "Switch Mode" power supply essentially build by 3 blocks :

a) Line voltage rectifier and HF switch.

b) HF transformer.

c) low voltage rectifier and regulator.

These circuit types are definately not for newcomers, as they will very easy burn up in smoke by even the smallest mistake. More so, they can easily take out your house circuit fuse, leaving you in total darkness, on such mistakes.

Besides you WILL get quite a few electric shocks with this circuit, until you have learned your lesson.

lastly : this is the standard type of circuit found in almost any small charger for mobil phones, labtops etc. There is a huge selction of voltage and amperage versions on ready made units, for a few quid.

Thank you for the quick replay, I will definitely tread lightly and cautiously!

Can you tell me what component(s) in this circuit make up the power supply?

Anders53: Turn it around to top view, there you will find a small High Frequency transformer. The circuit here is a "Switch Mode" power supply essentially build by 3 blocks :

a) Line voltage rectifier and HF switch.

b) HF transformer.

c) low voltage rectifier and regulator.

These circuit types are definately not for newcomers, as they will very easy burn up in smoke by even the smallest mistake. More so, they can easily take out your house circuit fuse, leaving you in total darkness, on such mistakes.

Besides you WILL get quite a few electric shocks with this circuit, until you have learned your lesson.

lastly : this is the standard type of circuit found in almost any small charger for mobil phones, labtops etc. There is a huge selction of voltage and amperage versions on ready made units, for a few quid.

That is a bit hard to answer, as all components are needed to make the circuit work.
There is really nothing in this circuit you can use as a stand alone circuit for experimenting or modifying.

Your question tells me, that you better keep hands off this project, you dont have the required experience in electronics.
I’m not trying to turn you down, just trying to keep you off a circuit that is very dangeropus to work with, when you dont have the experience.

I urge you to find something else as a project, where only safe low voltage is involved.
Ordinary power supplies with good old fashion transformers are much easier and safer to experiment with.
As long as you keep hands off the high side of the transformer.

You seem to have posted the same picture for both top and bottom view. Most improbable. :grinning:

Note that there is a modest separation on the circuit board between the mains components and the low voltage components, with the opto-triac straddling the divide and the word "Danger!" denoting the mains side.


Anders53: Your question tells me, that you better keep hands off this project, you dont have the required experience in electronics. I'm not trying to turn you down, just trying to keep you off a circuit that is very dangeropus to work with, when you dont have the experience.

Amen to that!

Strange, fixed that pic... thank you!

I appreciate the concern over high voltage, fortunately I do have the shocking experience to help guide me !

Still, the question remains on where (the components) and how the power is transformed?

Paul__B: You seem to have posted the same picture for both top and bottom view. Most improbable. :grinning:

Note that there is a modest separation on the circuit board between the mains components and the low voltage components, with the opto-triac straddling the divide and the word "Danger!" denoting the mains side.


Amen to that!

Thanks for the concern, I do appreciated it.

However, I am nosey and always need to learn and investigate... sometimes to my detriment!

Anders53: That is a bit hard to answer, as all components are needed to make the circuit work. There is really nothing in this circuit you can use as a stand alone circuit for experimenting or modifying.

Your question tells me, that you better keep hands off this project, you dont have the required experience in electronics. I'm not trying to turn you down, just trying to keep you off a circuit that is very dangeropus to work with, when you dont have the experience.

I urge you to find something else as a project, where only safe low voltage is involved. Ordinary power supplies with good old fashion transformers are much easier and safer to experiment with. As long as you keep hands off the high side of the transformer.

Hi,
Anders53, can you circle on the image where these components you have identified are.
I see,
Fuse with spare fuse.
Series voltage dropping Capacitor
Series current limit resistor
Filter Cap.
Regulator.
On the other side of the PCB is the rectifying components.

So circuit is still connected to the mains supply, no isolation.
These controls are built for cost and so everything is just doing its job, no overheads.

If you look you will see what possibly is a micro-controller so this is a programmed controller.
Not sure how you are going to modify it if its software controlled.

Tom… :slight_smile:

I see a micro, supplied by a capacitor directly from the mains. Driving two triacs via opto couplers. I don't see any switch-mode supply.

A capacitor/resistor supply is cheap. Problem is that it's not mains isolated. It's only "safe" when you're 110% sure the cap is connected to the phase line of the mains power. Controls must have plastic shaft/knobs. Leo..

How cute! The two MOCs are in the same position on opposite sides of the PCB.

Right! No transformer. Should have guessed the reason for such a whopping capacitor.

So - the whole thing is "live". Like many early valve radios, it is "transformerless".

Wawa's link explains it all.

You are right guys - Since I never saw the top view (until now after the image correction) I assumed the large soldering joints were from the wellknown switch transformer.

This is a cost optimised charger circuit of some kind which would connect any connected device on mains potiential. Not allowed in my neck of the woods, so rarely seen here.

I would not allow such a device in my house, considering my small grandchildrens ability to pick up just about anything and taste it.

A capacitive power supply has it's advantages. I have a small night light in the hallway that runs on a capacitive supply. 100n+1Kohm (fuseable), a tiny bridge rectifier, a 100uF cap and a green high efficiency LED. Fully encapsulated though, including the LED. Been plugged in for ~5years now. Running 24/7. Leo..

Anders53: I would not allow such a device in my house, considering my small grandchildren's ability to pick up just about anything and taste it.

Maybe not.

If you look at the description, this is inside some sort of griller - a "toaster oven" or similar - an internal part of an appliance. Not so easy to just pick up and chew on. :grin:

You may already be using one.

Wawa: A capacitive power supply has it's advantages. I have a small night light in the hallway that runs on a capacitive supply.

I think you will find that most of the current LED bulbs of less than 10W would be using capacitors. They use many SMD LEDs in a series string, presumably fed by a capacitor, then a bridge rectifier so that the full AC cycle is used at a minimum current.

That said, I do have a couple of the cheap Chinese switchmode converters for driving 3W LED chains.