Transformerless power supply

[Gantronics]

Hi ^__^

How are you everybody ? ...

I need some help ...

I have a friend that is making a transfomerless power supply , he wants to have 1 or 2 A of it ...

I searched but I didn't find any circuit that give that much from a transfomerless power supply ...

Some people say it is possible & others disagree with them ...

Can a transfomerless power supply give 1 A or 2 A ? explanation if possible please ...

Thanks a lot ...^__^...

 

[crutschow]

Transformerless supplies are dangerous and generally shouldn't be attempted by a beginner. What voltage does he want (I assume he wants DC)?

 

[tcmtech]

Yes you can. It's the same as building a small one but with larger components however just as the small ones are not line isolated this one would not be either.

Sorry but I can't upload a schematic at this time.

 

[ronsimpson]

What most people call transformer-less is not isolated. This means the output is on the power line so you can get shocked. Most power supplies are isolated from the power line. (safe)

Most transformer-less can only supply 20mA or so.

 

[Gantronics]

To crutschow

Thanks for the advice , I am assuming he is not a beginner ^__^ , 12VDC 1A or 2A ...

To tcmtech :

Thats what I want to hear , as for other power supplies (the ones that have transformer) I can upgrade it to give more current by using other components that can take more current (because I totally understand how it works ) , but for the transformerless power supply I cant do that because there is parts where I don't understand how it works in the circuit , for example lets take this picture : **broken link removed**

The Zener diode & the rectifier diode and the electrolytic capacitor will be upgraded to others that can take 1A or 2A (the cap will be higher capacity idk why ) , this is the easy part ...

But the hard part is the resistor and capacitor at the beginning "AC side" , I dont know what to do with them to reach the value I want , the resistor maybe I will rise its wattage (5watt instead of 1 watt) " am I right?" what about the capacitor?...

Thanks very much ...^__^...

To ronsimpson :

Thanks for the advice and information ...^__^...

 

[ronv]

The problem is it will be bigger and more expensive than a transformer supply. The capacitor will get very large as will the zener diode. The current limiting resistor will also be high wattage. Just not a real good idea for high current.

 

[ronsimpson]

in post #5 the circuit is good for 15 ma.
you want 1.5A thats 100x

 

[crutschow]

To crutschow

Thanks for the advice , I am assuming he is not a beginner ^__^ , 12VDC 1A or 2A ...

.....................................

Well anyone who wants to build a 12Vdc, 2A transformer-less line-powered supply rather sounds like a beginner.

 

[alec_t]

Why does your friend want a transformerless supply? Apart from being potentially lethal, as Ronv pointed out it will be more expensive than one using a transformer.

 

[MrAl]

Hi,

I'd like to find out what this is going to be used for. Why does he want this kind of power supply?

Transformerless power supplies are used on a lot of equipment. But for most of that stuff the guts are never exposed to possibly human touch. No connections accessible from the outside of the box, so that means a lamp dimmer might be ok but a battery charger would not really be safe. Even for the lamp dimmer special attention has to be paid to the type of pot being used so that the shaft can not become electrified.

In fact, wall transformers used for consumer products have to pass a double isolation test to be allowed for use in the USA and maybe other countries too. That means the secondary is isolated from the line voltage via two forms of insulation.

 

[ronsimpson]

I have played with a 12V 300mA transformer-less power supply. It is a buck supply not a capacitor supply.

A switching power supply the size of a 'wall wort' could give you 12V at 2A and give isolation.

 

[tcmtech]

But the hard part is the resistor and capacitor at the beginning "AC side" , I dont know what to do with them to reach the value I want , the resistor maybe I will rise its wattage (5watt instead of 1 watt) " am I right?" what about the capacitor?...

All you really need to do is change the capacitance size to move the circuits equivalent series resistance to a lower value.



To get 2 amps off of a 220 VAC 50 HZ circuit you will need a capacitance of roughly 100 - 110 ohms which works out to the capacitor needing to be around 30 - 35 uf which is a common size range used in AC motors, air conditioning systems, and HID lighting ballasts.

The line side resistor could be dropped from the circuit entirely and the whole circuit can be redesigned to be a single 1 watt zener diode, a common 30 - 50 watt power transistor for the power dissipation, and a good sized electrolytic capacitor like something inthe 4000 - 10,000 uf 25 VDC range.

 

[hmsahir4u]

I am also interested such Transformer less Power Supply in same specification.
Congratulation to all members of this forum and the admin for updated new website.

 

[ronv]

If you don't have the line side resistor and switch it on at the peak of the AC cycle the diode currents will be really big as they try to charge the caps.

 

[ericgibbs]

I am also interested such Transformer less Power Supply in same specification.
Congratulation to all members of this forum and the admin for updated new website.

hi,
These two PDF's show the required calculations.
E.

 

[ronsimpson]

If we are really trying to get amps from this type of supply; see AN954 (second .pdf from EricGibbs) near the end there is a circuit with full wave rectification. (4 diodes) I think getting current from both side of the cycle is important.

I do worry about 33uF on the power line. There is a requirement that the cap must discharge within a certain amount of time. Also the inrush current could be high. I would look at positive temperature resistors that are normally used for inrush limiting.

 

[unclejed613]

i grew up in a time where we had a lot of consumer equipment that had "AC/DC hot chassis" designs. the designers assumed that the outlets in homes were all properly wired. the main problem was that in many instances, the AC outlets were not "keyed", or if they were, they might be wired backwards. this made the chassis, which was supposed to be at or near ground potential, "hot" (at 120Vac).
as long as the equipment was isolated in it's plastic case with plastic knobs, everything was ok. but there were guitar amplifiers etc, that were made this way. when i was young and playing in a band, we did the "plug dance" to make sure everybody's equipment was properly plugged in. we kept a meter handy just to be sure...
even some rather large TV sets used this type of design. all of these devices were vacuum tube devices, and had the filaments wired in series across the line. with tube filaments, there could be a rather large inrush current as power was applied. the power supply itself was only a few hundred milliamps at 150Vdc, as tubes really didn't require as much current. then, somewhere along the line, there began to be regulations and such that required about 1500V or more isolation between the power line and chassis, and many manufacturers who were already switching over to solid state, also went back to transformers. then switching supplies were developed that reduced the need for "big iron" but were able to maintain the high isolation.

 

[tcmtech]

I do worry about 33uF on the power line. There is a requirement that the cap must discharge within a certain amount of time. Also the inrush current could be high.

At that low of capacitance it's not really an issue with inrush current or at least it's no different than when plugging in any large SMPS, electric motor, or HID light that uses large value capacitors in its circuitry.

Relating to bleed down resistors yes if the OP did not use a capacitor from one of the sources mentioned that came with a built in one then he should consider using a 100 - 250K 1 watt across its terminals.

 

[ronsimpson]

At that low of capacitance it's not really an issue with inrush current or at least it's no different than when plugging in any large SMPS, electric motor, or HID light that uses large value capacitors in its circuitry.

In a SMPS the inrush current flows through the diodes and charges the filter cap. The load does not see this current.

In this "capacitor" supply the inrush current flows through, not only the input capacitor, but also through the filter capacitor.
example: Input cap=33uF, filter cap=330uF, To get the input cap charged to 200V the filter cap will charge to 20V. If the filter cap is smaller the inrush current will (can) over charge the cap. If there is a Zener across the filter cap, the Zener must carry the inrush current.

I have built these power supplies to power LED night lights. I use the Zener function of the white LEDs to limit the voltage across the filter capacitor. Some times the inrush current is very high. (LED current is high) This depends when the power is applied (when with in the sign wave from the power company).

 

[tcmtech]

Yes however as I mentioned earlier for a 2 amp power supply using direct line coupling I would not use a filter cap anywhere less than 4000 uf.
Personally given it's being fed by a half wave capacitive source I would be using closer to 10,000 uf myself.