Re: Question: simple inverter to fire up a switch mode power supply?

From: Mac (foo_at_bar.net)
Date: 12/14/04 

Date: Tue, 14 Dec 2004 06:03:56 GMT

On Tue, 14 Dec 2004 15:42:40 +1100, Walter Lolham wrote:

> Hi there,
>
> I am not an electronics guru, just know enough to be dangerous and need
> some help on the following.
>
> In a switch mode power supply, in the first stage the 110/240 volts
> mains power goes into a bridge rectifier and becomes DC and gets
> filtered by a large capacitor giving around 150 -> 350 volts DC.
>
> Now to use such a power supply say with a 12 volt battery, an inverter
> would be the easiest solution. But since inverters are not very
> efficient (heat, loss in the transformer etc), do you think if the
> following solution could work?
>
> If I oscillate the 12 volt (similar to an inverter), but rather than put
> it across a step up transformer, instead I feed it into a diode/cap
> bridge to multiply the voltage N times to give me the required voltage
> (say around 180 volts) to charge the large cap in the primary stage of
> my switchmode power supply. Given the current is sufficient, do you
> think it could work?
>
> If it does, advantage is that it will be much simpler, cheaper and
> smaller to build inside the box, on top of being more efficient.
> Secondly when there is no load or if the load is minimal, battery
> consumption will be next to nothing as opposed to an inverter which
> still has to chop the primary of a relatively large transformer, which
> in theory is a load in itself.
>
> Any thoughts/suggestions would be appreciated. If you know of a suitable
> circuit that you could point me to, I'll appreciate it even more.
>
> Regards,
> Walter.

I think you could replace the switch mode power supply altogether with an
off-the-shelf DC to DC converter. This would be the easiest thing for you
to do.

--Mac

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