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Looking for dirt cheap method DC power supply

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Space Varmint

New Member
Anybody got a short cut that will deliver maybe 100 milliamps? I don't want to use E cores. I would like to use a small toroid transformer. I only need to power a 6 pin PIC processor and a transistor to switch an SCR that will trip a solenoid actuated switch. The AC will power the solenoid directly through the SCR.

I'm hoping I can find a cheap chip that will take a direct AC input and using maybe, only a toroid and a tantalum cap I got about 6 volts at 100mA.
 

Sceadwian

Banned
Why not an e-core? It's a whole lot easier that hand winding a toroid.
 

Sceadwian

Banned
I'm personally a big fan of discarded cell phone chargers, they usually put out 5 volts and are smaller and much lighter than transformer supplies.
 

Space Varmint

New Member
I'm personally a big fan of discarded cell phone chargers, they usually put out 5 volts and are smaller and much lighter than transformer supplies.
This has to be replicatable. Hmmm....might have invented a new word. But yeah, I can't really use another power supply. What I have against the E core is it's size. This has to be small. It will be inline in an AC power cord.
 

ericgibbs

Well-Known Member
Most Helpful Member
This has to be replicatable. Hmmm....might have invented a new word. But yeah, I can't really use another power supply. What I have against the E core is it's size. This has to be small. It will be inline in an AC power cord.
hi SV,
Is a wall wart psu not applicable.?
 

Sceadwian

Banned
How small? For 120V to 6 volts you'd need 20-1 turns ratio and enough inductance on the primary to keep the quiescent current down. Depends on the core material and it's size. I'm not even sure how to go about calculating how many turns you'd need to do that, so you'll have to experiment with it. Any way you look at it it's going to be large, sure toroids are better than e-cores but not THAT much.
 

Space Varmint

New Member
How small? For 120V to 6 volts you'd need 20-1 turns ratio and enough inductance on the primary to keep the quiescent current down. Depends on the core material and it's size. I'm not even sure how to go about calculating how many turns you'd need to do that, so you'll have to experiment with it. Any way you look at it it's going to be large, sure toroids are better than e-cores but not THAT much.
No, can't use wall wart to the other guy.

I guess I'm not as concerned about the transformer. That is something I could work out later. What I need right now is a chip. Do you'all know of any cool chips where I could run the AC straight into the chip and just have a few external parts to pull it off? I mean, I could do this using a diode bridge rectifier and all, but I know there are allot of chips out there that have all that in them. Maybe Maxim would have one. I'm just sorta tapping the knowledge banks of the group, where maybe someone has done something like this recently so I can go after the latest & the greatest.....cheap and small.
 

blueroomelectronics

Well-Known Member
One of the Microchip app notes shows a transformerless PIC supply. A few caps & diodes. Problem will be the size of the 1uF high voltage cap.
 

Space Varmint

New Member
One of the Microchip app notes shows a transformerless PIC supply. A few caps & diodes. Problem will be the size of the 1uF high voltage cap.
Not a problem. I could use tantalum. You know, Coltan type cap. But yeah I would like to find that link because I will be using a PIC, the PIC10F206.
 

tcmtech

Banned
Most Helpful Member
Thats an easy one!
This is as simple of regulated power source you can get thats directly line powered.
The AC cpacitor value should be matched to give you about 20 Ma or so higher than what the circuit uses at peak amps draw. :)
 

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Sceadwian

Banned
Sure, use tantalum caps if you want to create a small ball of plasma where your pic used to be the first time the power line spikes. You could use a simple non-isolated buck converter, the Art of Electronics has an example on how to build a line powered buck converter which could probably be adapted, again though for 100ma's a standard transformer/bridge rectifier is really not that big. you're only saving 50% space and some weight at most.
 

tcmtech

Banned
Most Helpful Member
Am I missing something? Where did the idea for Tantalum Caps at 250 VAC and what not come from?
Right now I feel like I am watching a dyslexic and an autistic have an argument! :D
 
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