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Transformer less Power Supply

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Suraj143

Active Member
I need to make a reliable transformer less power supply to my infrared project.Attached a drawing & needs comments.

Relay takes 30mA Current.A total current of 40mA-50mA more than enough for me.
 

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Last edited:

schmitt trigger

Well-Known Member
Looks good.
But...........in transformerless supplies it is always good practice to reduce the total current draw.

For instance:
I assume that your relay is 30 mA @ 5V.
If you change the relay coil to 12V and feed that from the voltage previous to the 7805, then a similar relay will only draw about 12.5 mA.
You would need an external NPN transistor to drive it, but those are really, really cheap.
 

ronsimpson

Well-Known Member
Most Helpful Member
The 1N4007 could be 1N4001. There is no high voltage on these diodes.
---------edit--------
The voltage is high across the 1M resistor. Many resistors can not take that much voltage. You might need to use 2, 3, or 4 resistors to reduce the voltage each.
 
Last edited:

Suraj143

Active Member
Hi thanks for the view.

Regarding the voltage across 1meg...

(230×1.414) - 30V = ~300V
V=IR
300=I × 1000000
0.3mA = I

You mean 1/4w resister not enough?
 

MikeMl

Well-Known Member
Most Helpful Member
...
You mean 1/4w resister not enough?
Resistors have a maximum voltage rating, as well as a maximum power dissipation rating...
 
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