Buck for low power application

[BenoitR]

Buck for low output power application

Hello,

I need to implement a buck converter in a specific application that required very low output power. Capacitive and resistive power supply are not possible to use because of too high power losses or too high input peak current.

My requirements are:
- input RMS voltage : 90 to 260 V / MAINS frequency : 50 or 60 Hz
- Output DC voltage 12 V / DC current : 2 mA => 24 mW in steady-state mode !
- Stand-by comsumption : lower than 0.3 mW !
- Maximum input current : 15 mA

I have test a VIPER06, but stand-by losses max is 30 mW (higher than my steady-state consumption).

I don't find any converter adapted to my above requirements, but I don't really know which manufacturer are specialists in low output power converter.
Feel free to propose me some converter reference, or tell me if lack of information about my application.

Thanks,
Benoit

 

[mtwieg]

Re: Buck for low output power application

Such high voltage, low power converters aren't really feasible or cost effective. After all, who cares about 30mW of standby dissipation?

If you really want such specs you'd have to build your own specialized circuit, probably using a huge inductor and operating at a very low frequency. Even then 0.3mW of standby consumption is likely not possible. You're talking about a couple microamps from 260VAC...

 

[BradtheRad]

Capacitive drop could be suitable for this purpose. It does not generate much heat, since it uses capacitive reactance to drop a large amount of the mains AC.

Screenshot:



C1 must be non-polarized.

R1 is not essential to proper running, but it is advised in order to limit inrush current. I used a value that allows use of a 1/2 W size, which is inexpensive and common.

The 12V (or 12.1V) zener diode dissipates up to 160 mW.

You will need to find the right balance between C1 and R1, in order to work with your wide supply range of 90 to 260 VAC.

 

[BenoitR]

mtwieg,

I'm care about these 30 mW. It's higher than my output consumption. Which manufacturers are specialists of low power converters ?

BradtheRad,

I cannot use a capacitive power supply because I have switch (Triac) in parrallel of this power supply that I turn ON every 10 ms. Then the capacitor will be discharge at each switch turn-on, that induce too high power losses (~5W in the worst case).

Thanks for your help.

 

[FvM]

Off-mains switcher usually don't care for a few mW. Thus it's unlikely to find a ready made IC. Looks like you need to assemble the solution from discrete components.

 

[BenoitR]

I take care about the power consumption because I have a load in series with my application on the MAINS. This load could be disturbed by a too high current sunk from the MAINS, its the reason I need a SMPS.

Questions:

1/ Did you know a good tool to design a buck converter fastly ?

2/ Which manufacturers are specialists of low power converters ?

 

[mtwieg]

I'm care about these 30 mW. It's higher than my output consumption.

If you were operating from a small solar cell or a battery then that would be a concern, but not when you're pulling power from the AC line. Consider that the same AC line is probably providing a couple kW to nearby loads, and 30mW on average costs a couple pennies per year...

I take care about the power consumption because I have a load in series with my application on the MAINS. This load could be disturbed by a too high current sunk from the MAINS, its the reason I need a SMPS.

Your circuit and supply are in series with a load? This isn't making much sense.

2/ Which manufacturers are specialists of low power converters ?

Linear Tech makes some micropower buck converters, but only for low voltage DC/DC applications. Power Integrations makes simple low power AC/DC converters, but none of them even come close to your requirements.

 

[BenoitR]

Your circuit and supply are in series with a load? This isn't making much sense.

It has sense, you could have a LED lamp converter in series with a light dimmer for example...

Thanks for the manufacturers, I will check their portfolio and I will post my results.

 

[BenoitR]

Hello,

Some news about my research:

- PowerInt devices : I have found a good candidate for my applications (very low stand-by consumption).
http://www.powerint.com/products/linkzero-family/linkzero-ax

- Linear Tech: I don't find any component with my input voltage requirement (No component with VIN > 150 V ?)

Did anyone knows another manufacturers able to fit my requirements ? (I would like at mean 2 manuf. for a comparison and/or to have a backup)