Transfermerless Power Supply

why dont all put forward your basic spec?

input voltage, output valtge.?

???

No offense intended, but (assuming you're talking about a mains PSU) are you OK working with live mains circuits? Without a transformer in there, it's quite easy to zap yourself.

Please take careful note of the caution re Mains Powered transformerless Power Supplies per JohnDG above.

What sort of "time delay" circuit are you using ?

Does it include any inductive components = wound coils with iron cores ?

If so the requirements for your power supply may be quite different.

As suggested by cnpower above, best to show here, what you have in mind.

......Whats your voltage and mode AC/DC with 80-100ma .....I remember some time ago cheap chinese rechargable torches charging 3.6V 270mah rechargeable battery with charging through small circuit consisting of resistors for volatage drop bridge diode capacitor for rectification and limiting resistors and zener diode . no transformer utilised , but you should be extremly precautious while working with such circuits .

Hi Vikas,

Thank for your reply. I am just a beginner. I here attached my circuit. Ac supply voltage is 220-240V. The problem is resistor 220 ohms. It emits heat. I like to put this circuit into small casing. thank you.

Hello again, Lionnel1967,

That Isolating capacitor will need to be rated "Low Leakage" and for 800 volts PIV.(Peak Inverse Voltage)

It would be far cheaper to use a tiny mains transformer, far safer too.

You do not give a location, but Maplin or RadioSpares (RS) in UK; Radio Shack in US; Dick Smith Electronics or Altronics in Australia or New Zealand, if they are near your location, would be able to assist.

If you are obtaining the IC and other parts shown in your schematic, ask that supplier for a small mains transformer, the cost will be around US$4.00, Aust$ 9.00, NZ $11.00 or less.

You will not then need that resistor, which wastes energy, generating heat which will become a problem, if placed and operated inside a small enclosure..

Please note that 240 Volts is quite unforgiving if you receive a shock and we prefer you remain alive.

Please advise here further, that way we know you are still alive....

Look at this link.

It shows a capacitor coupled supply circuit, You will have to tinker with values and I'm not sure if you will be able to draw enough current without BIG capacitors.

Like the others said, maybe simpler with a transformer.... but if you want to play, that circuit is a good start point.

(I've used similar it on a small commercial product which runs a microcontroller driving an AC pump. )

Careful with capacitor ratings, and earthing. (terms and conditions apply, every man is his own safety officer...etc blah blah blah)

Del

Two resistances will form a voltage divider that can be used to supply a lower voltage than the voltage applied to them. It will be more wasteful as regards its heat dissipation, which is why transformers are usually used.

As long as the time delay switch power is independent from the load being switched there are a number of solutions.

What voltages are you using is a good question that needs to be answered first.

Then what are you switching?

There are a number of different off-line supply circuit chips, from various manufacturers, out there that can handle maybe a watt of power with a minimum of components.

A resistor bridge is the least elegant and most wasteful approach to use. The diode rectifier with a zener diode regulator and a filter capacitor or two is still very crude but cheap and orders of magnitude better than a resistor bridge.