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Transformerless Power Supply @ 100mA

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ronsimpson

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There have been many low current designs posted. Most are for 1 to 5mA. It is hard to get much power from the "transformerless" style.
Here is a design of a one IC PWM "buck down" style. Inside the IC there is a 630V 300mA MOSFET. (DRAIN--SOURCE)
This part was not designed for this application but works. http://www.linear.com/product/LT8315
This IC is new to me. I did not build this. I have built several Buck, PWM, Transformerless Power Supplies.
High voltage will kill.
Vin is from the power line.
"GND" is from the power line and is not ground.
The "+12V" is not at ground but lives on top of the power line.
The "GND" pin on the IC is not ground! It has high frequency switching!
Do not connect the ground lead of a scope to any part of this circuit!

upload_2017-2-13_20-28-46.png
---edited---
I see there is a part missing!
You need to add a full wave bridge between the power line and the first capacitor at "Vin".
 

Mikebits

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I wonder who will be the first one to connect their scope ground lead to the circuit :woot:
 

dr pepper

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I've used Tny devices for similar ideas, brite power make ic's with minimal parts for led lights that work in a similar manner.
 

schmitt trigger

Well-Known Member
Here is another using parts from Power Int. I would use 4 diodes (bridge) for D1. Then C1,2 cold be smaller.


Do not connect the ground lead of a scope to any part of this circuit!
I would too...however the reason I believe PI decided to use a half wave rectifier is that if you employ a polarized AC plug, the "common" line would be just a few volts above ground, thus ameliorating safety issues.
 

dr pepper

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Using one diode saves money as not only do you loose 3 other diodes, you also lower the voltage saving more money on having a lower rated voltage bulk cap and lower voltage rating switching fets, plus on low power stuff half wave is probab enough.
I built a line supply for a pyrography pen, 2v at 50a, it doesnt have rectifiers either end, the o/p is 50khz with 100hz ripple, and it works fine.
 

Mikebits

Well-Known Member
You don't need to - the load will simply take what it needs.
This seems to be a very common question, I have seen the topic come up countless times. Maybe somebody (Not me) would like to write up a little tutorial explaining this topic, and making it a sticky :)
 
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