Transformerless 5v 40 mA source

320

05:41:57

Use a LM7805 in place of transistor and its zener.
Use 1W 12 V zener and 2W 50 ohm resistor. 
The work principle is simple, capacitor in series has an impedance of 5.5kohm, so the max current is 35  mA.
12 V zener avoid high voltages on lm7805 (transistor here).
Use a 100 mA fuse for safety. Varistor would be nice too.

Ps: tested this circuit today (20/06/2019) on protoboard. It worked fine. powered a ATMEGA328 p with 1 led and a moving sensor. 
Notice this circuit has a huge capacitive reactive power of about 10 VAr. It is nice for correction (not much) of your power factor if it is indutive.

published 6 years ago

PrathikP

6 years ago

It's not smart to use a series regulator for such a circuit. The voltage that the filter cap holds depends on the current draw from it. If the current draw drops really low, it can charge up beyond its rated voltage and blowup. It could also blow up the series regulator by exceeding it's max input voltage. And if the current draw drops to zero (aka no load), the capacitor will charge up to the peak of mains voltage. So it is imperative that you use a shunt voltage regulator.

PrathikP

6 years ago

And 60Hz 219V pk is quite odd.

ewric

6 years ago

Tks for repply.

ewric

6 years ago

Made the necessary changes. Anything you desagree, please, comment. I will use a source like this to power atmega and a infrared detector and transmitter to swith an air conditioner

BillyT

6 years ago

120Vrms is 170Vpeek

hougaarden

6 years ago

You do not have a galvanic isolation, this circuit is dangerous! For a few Euro/Dollar you can buy a 5V switching PSU.

ewric

6 years ago

Here we have 220 Vrms, 310 Vp. Yes, this circuit has no galvanic isolation. It shall not be used in products will be used manually. In my case, this circuit will work with no human contact. It will stay glued to the ceiling room. It will power an Atmega that will identify movement in room and switch on the Air conditioner. For safety, a 0,2A fuse will be used. Despite galvanic isolation is important, on switching power supplies you still have the problem. If the transformer short circuits, it will lead high voltage to secondary. If the switching transistor shorts, it will lead high voltage to pwm control chip. Avoiding high voltage in both systems is inevitable. Mine will be a little better than chinese ones because it will have fuse.

ewric

6 years ago

Room's ceiling***

hougaarden

6 years ago

As long as you know what you are doing. We don't want to lose you (yet) 😊

rich11292000

6 years ago

Hope those are reference grounds and not earth grounds.

ewric

6 years ago

、no, they are not. If they were, when i connect life in the up sine wave, the circuit would just blow up.

ewric

6 years ago

Not earth ground*

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