Hello!
I need a schematic for a mini switcher with a few components only. It has to be powered by AC 220V in has to produce DC 12V.
It will be used as PSU for one relay and IC 4027. I supose that 500mA should be enough.
Does anyone have an idea how should this be done? I was hoping that i could use an IC, but i'm not sure that it is possible.
Regards,
DJG
I need a schematic for a mini switcher with a few components only. It has to be powered by AC 220V in has to produce DC 12V.
It will be used as PSU for one relay and IC 4027. I supose that 500mA should be enough.
Does anyone have an idea how should this be done? I was hoping that i could use an IC, but i'm not sure that it is possible.
Regards,
DJG
what about one of these ?
http://www.futura-shop.com/pdf_eng/1350-VB409SP.pdf
- only about 30 mA tho
Or
You can use a cap. to reduce mains voltage.
Be careful with mains plz
http://www.futura-shop.com/pdf_eng/1350-VB409SP.pdf
- only about 30 mA tho
Or
You can use a cap. to reduce mains voltage.
Be careful with mains plz
If you are only driving a relay and a mini IC, it would be best to just use a low frequency main transformer with rectifier and cap filter. The previously mentioned part will dissipate huge amounts of power and will require a heatsink. Also the minimum output current on this part is 80mA much higher than your required minimum. You may have trouble there.
If you are using this for a soft-start circuit and you don't need it to be ground referenced, you can build a very simple supply by placing an X-cap in series with a bridge rectifier, and put a Zener and filter cap on the output of the rectifier.
The cap will drop most of the voltage, and approximately set the maximum available current. The Zener regulates the voltage. You don't need a resistor in series with the Zener because current is limited by the cap impedance.
You will need to play with the input cap value because too low a value means you won't have enough current and too high a value means that you will have to dissipate all the surplus current in the Zener.
I plan to use a circuit like this for a soft-start circuit where I want a relay to short a resistor after some delay. For a 120VAC, 60Hz system, I plan to use a 1.2uF cap on the bridge input and a 12V Zener on the bridge output. I expect a max available current of about 50mA. My relay draws about 33mA at 12V. A 2200uF input cap should give me about 1-2sec delay before the relay kicks in. If the timing is not well controlled with jsut a relay, I'll add a transistor or two to get a mor econsistent delay.
Use an X-cap for the voltage dropping cap, since these caps are safety rated for across-the-line use.
I'll try to put up a picture Monday. I've only simulated the version described above, but I've used a half-wave version of this in a product that will be going commercial soon (non-audio). I did not invent it, but I forget where I first saw it (maybe in a Microchip app note?).
John
The cap will drop most of the voltage, and approximately set the maximum available current. The Zener regulates the voltage. You don't need a resistor in series with the Zener because current is limited by the cap impedance.
You will need to play with the input cap value because too low a value means you won't have enough current and too high a value means that you will have to dissipate all the surplus current in the Zener.
I plan to use a circuit like this for a soft-start circuit where I want a relay to short a resistor after some delay. For a 120VAC, 60Hz system, I plan to use a 1.2uF cap on the bridge input and a 12V Zener on the bridge output. I expect a max available current of about 50mA. My relay draws about 33mA at 12V. A 2200uF input cap should give me about 1-2sec delay before the relay kicks in. If the timing is not well controlled with jsut a relay, I'll add a transistor or two to get a mor econsistent delay.
Use an X-cap for the voltage dropping cap, since these caps are safety rated for across-the-line use.
I'll try to put up a picture Monday. I've only simulated the version described above, but I've used a half-wave version of this in a product that will be going commercial soon (non-audio). I did not invent it, but I forget where I first saw it (maybe in a Microchip app note?).
John
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