All of us are using micro controllers, small home made circuits. Most of the time I'm facing to power some of my small devices based on micro controller and also the 433Mhz transmitter receiver modules which are permanently connected in house. I want to ask you is it safe for the circuit to use simple zener-capacitor converters to produce 5V,12V from the direct 230V AC line? will fluctuations in the line affect my circuit working like if im powering to a RF receiver in this way? suggest me a good way of designing this kind of power converters which will be reliable and safe to my devices.
Is there any kind of modified version that can be categorized in an acceptable reliability? to reduce the sudden spikes. it is just for my experiments.
You need isolation to make it safe. The normal method is using a transformer and if you have a transformer you might as well use it to drop the voltage. Then use a voltage regulator chip, much more effecent than a shunt Zener.
I decided to build a transformerless power supply, which brings mains voltages from 110 RMS AC (155 v. peak) down to 70 v. "rough" DC, then to a very solid and well regulated 40 v. via a switching circuit. It can supply up to 4 amps. with tight regulation, and saves the weight and cost of a big 4 amp. capable transformer. Realizing that I didn't have the isolation, I built a DC GFI circuit as follows. I put a 0.1 ohm resistor in the current return path, and another in the current supply path. I then set up a 50% voltage divider across these resistors (from input on one to output on the other) and another across the other ends. If the current in the two 0.1 ohm resistors is equal (i.e., no leakage) then the voltages at the center of these dividers is equal. If there is current leakage (ground fault), the voltages are out of balance, and I use an opamp in comparator configuration to detect that and shut down the circuit.
This has been proved out in simulation, but as with any circuit, it will take a good bit of tweaking to get there. I think its legal in the U.S., because many items in the U.S. depend only on GFI to protect the users from shock.
jrdoner:
This has been proved out in simulation, but as with any circuit, it will take a good bit of tweaking to get there. I think its legal in the U.S., because many items in the U.S. depend only on GFI to protect the users from shock.
So what you are essentially saying, is that it is safe unless it (that is, your protective circuit) malfunctions.
What by the way are those dangerous items you mention protected only by a RCD?
Most of us rely on the very available "wall wart". You can buy the "regulated" type in almost any voltage you need. There are even models with DUAL outputs. Look at Jameco.com, they have a huge variety and you won't electrocute yourself trying to reinvent the wheel.
I think its legal in the U.S., because many items in the U.S. depend only on GFI to protect the users from shock.
I don't see how this can be true, because only outlets near water are required to have GFCI protected outlets. And there is the issue of outlets wired incorrectly, which I've heard is not uncommon.
I've never taken apart a wall adapter and found a transformerless power supply. Are you sure you weren't just looking at switch mode power supplies with very small transformers?
be80be:
Oh I'm getting forgetful ceiling fans with remotes use them and garage door openers with remotes and them cheap 433mhz remotes
Those are isolated through the remote, that is another matter entirley.
The main point of legislation in the US is the prevention of fire. Where as in Europe the concentration is the prevention of electric schocks. This leads to major differences in the safty regulations each side of the pond.
MarkT:
Note that in the AppNote all the supplies are directly on the live side with the series resistance or capacitance on the neutral side...
(perhaps there's an assumption that the circuit will be driving a Triac as a live-side switch)
I'm surprised that the AppNote doesn't have a reference date of first April 2004.
You must take that app note in context. It is designed to be used with a double insulated self contained system. It is not an open invitation to make general purpose power supplies.
It could be used for things like a desk light or the electronic control of a washing machine or oven. Something that is a compleate system where the user is never exposed to the low voltage.
The problem is that inexperienced people see the circuits and do not understand the limitations.
Grumpy_Mike:
You must take that app note in context. It is designed to be used with a double insulated self contained system. It is not an open invitation to make general purpose power supplies.
What is really disturbing in that context, is those sort of modules cited on eBay!
