Transformerless AC DC Power Supply

[samEEEf]

I think one of the problems of such transformerless power supply is short circuit fault of the zener diode and the series capacitor. Am I right? I'm telling this thing because open circuit fault will not burn the target circuit. How can I protect the target circuit from short circuit fault?

 

[tpetar]

For short circuit you can use fuses on both sides L/N. If capacitor have some problem this can be dangerous, even can cause burning and fire at parallel resistor, all depends from particular situation.

- - - Updated - - -

We didnt hear recently thread owner Paradigm, maybe he is tased with voltage.

 

[samEEEf]

If I use capacitor voltage divider to get voltage across one of the capacitors around 7-10v and use voltage regulator IC like 7805, will it be better (and/or safer) than the conventional transformerless power supply? Being capacitor voltage divider circuit, no power is dissipated except in 7805 IC.

 

[tpetar]

This design is not isolated and cannot be considered as safe, but is better for one step with 7805 compared to zener diode.

You have problem with space in device case or with price of psu ?

 

[tpetar]

See this good material about cheap death :




Do NOT make this !!!



**broken link removed**

Read Chapters 7 and 8 its very important.

 

[mtwieg]

Do NOT make this !!!

View attachment 88267

**broken link removed**

Read Chapters 7 and 8 its very important.

WTF Microchip?? Can't believe they published this.

edit: ahahaha

the connection of neutral to earth should be harmless since they are supposed to be at the same potential. If they are not, it suggests a wiring fault, or other issue.

My diploma just burst into flames reading that.

 

[tpetar]

WTF Microchip?? Can't believe they published this.

edit: ahahaha

My diploma just burst into flames reading that.

Yes my friend, everyone have shiny moments.

Because of that, specially when mains power is used we need active brain which think, not just worker which just look to make and complete device based on some given circuit.

Everyone can make mistakes.

:wink:

 

["electri"]

yes, there are safety concern if you are first converting ac to dc and then stepping it down by the regulators ,dc handling is far more risky than ac , further more you will need a large value inductor which poses constrains in working with high frequencies. as far as i phone chargers are concerned so their chips are manufactured at foundries with preciseness taking into account of losses ,trying to make it manually will result a large amount of loses.

 

[tpetar]

yes, there are safety concern if you are first converting ac to dc and then stepping it down by the regulators ,dc handling is far more risky than ac , further more you will need a large value inductor which poses constrains in working with high frequencies. as far as i phone chargers are concerned so their chips are manufactured at foundries with preciseness taking into account of losses ,trying to make it manually will result a large amount of loses.

Prices for iPhone 3G per parts:
http://www.adbi.org/files/2010.12.14.wp257.iwutdp.tab.1.pdf

I think for price difference between that and full market price, device should be better. At least to increase the salaries of workers in China, which complete this device by hands.





See this SMPS psu, output voltage can be easily adjusted, this can be made in SMD version and with tight PCB can be very small :



- - - Updated - - -

WTF Microchip?? Can't believe they published this.

edit: ahahaha

My diploma just burst into flames reading that.

Also read what Rod Elliott get on email as official answer from anonymous.

I hope that thread owner did not try this circuit from TB008, we didnt hear him from first post. :-?:smile:

 

[samEEEf]

This design is not isolated and cannot be considered as safe, but is better for one step with 7805 compared to zener diode.

You have problem with space in device case or with price of psu ?

Problem with space.

 

[tpetar]

Problem with space.

My thinking :

1. To use external PSU small mains SMPS adapter for mobile phone 5V output, and connection with device is made over some connector, such as micro USB, mini USB, .... or any other, you can change it easily.

2. Extract PCB from that small SMPS and put it in your device case. That SMPS PCB size is almost the same needed to transformeless (capacitor, resistors, regulators,...)

3. To make your or buy smaller PCB SMPS completely maded in SMD. This can be very very small.

4. Usage of epoxy sealed AC/DC converter module. Not cheap but you didnt mention price as factor. :smile:


When you are not sure what you are doing, or you are starter, then respect and use well known traditional things. Always is good to ask, maybe someone have to suggest some different solution.


:wink:

 

[samEEEf]

No idea about epoxy sealed AC/DC converter. Is it able to convert 230V ac to 5V dc?

I'm planning to make a timer circuit inside a cube of dimension 1.3"x1"x0.7". I wonder whether it is possible to fit a PS inside it with a 8pin MCU, 6pin optoisolator and a TRIAC.

 

[tpetar]

No idea about epoxy sealed AC/DC converter. Is it able to convert 230V ac to 5V dc?

I'm planning to make a timer circuit inside a cube of dimension 1.3"x1"x0.7". I wonder whether it is possible to fit a PS inside it with a 8pin MCU, 6pin optoisolator and a TRIAC.

Use adapter like for mobile phone. All AC to DC is done in adapter at mains wall socket, 5V travel over wire to your device. This is principe of any gadget and mobile phone or any other mini device today, even laptops uses similar method.

**broken link removed**

Prices is around few euros, cheapest chinese with small SMPS inside 1-1,5eur.

You can use AC/DC converter in module, but price is little higher, and these modules should go inside in device case, usuallz is soldered on PCB :

**broken link removed**

Prices around 8eur and up, depends from power and specifications.

 

[samEEEf]

Yes, today's mobile phone chargers are extremely small. Those come with 500mA to 2000mA. I don't need such large amount current indeed. I need only 40-50mA of current at 5v DC. that's why I was thinking of a small, simple and low cost good PSU.:smile:

 

[tpetar]

Yes, today's mobile phone chargers are extremely small. Those come with 500mA to 2000mA. I don't need such large amount current indeed. I need only 40-50mA of current at 5v DC. that's why I was thinking of a small, simple and low cost good PSU.:smile:

Its not problem, and its better that psu is stronger that you need, that means that you can use 2A psu adapter freely to supply your device with 40-50mA. Your device will use only how much is need, and you support and can handle up to 2A.



:wink:

 

[samEEEf]

Yes, I know this. But using a 2A PSU only for 50mA demand is not a good design. 50mA PSU should be more compact in design as well as cost effective. So, for this low current demand I wanted to make transformerless PSU with better possible way. That's why I thought to use a 7805 (To-92) if it gives better result.

 

[samEEEf]

One thing that just came into my mind is - if I use connect filter capacitor (e.g, 470uF) across the Zener diode what will happen? For capacitve transformerless PS, a capacitor with high voltage rating (higher than 230V line) is used to limit the current through the zener. Usually the capacitance is low e.g, 0.47uF. So, it seems to be a voltage divider of 0.47uF and 470uF. As the impedance of 470uF is much lower than 0.47 the voltage across the filter capacitor will be much lower. In this condition how we will get the required DC of 5v?