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

From: Allan Herriman (allan.herriman.hates.spam_at_ctam.com.au.invalid)
Date: 12/14/04 

Date: Wed, 15 Dec 2004 01:10:23 +1100

On 14 Dec 2004 10:34:37 GMT, chrisgibbogibson@aol.com
(ChrisGibboGibson) wrote:

>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.
>>
>
>Multipliers are very inefficient.
>
>Transformers can be one of the most efficient devices around. 95% is very
>common. 98% is quite easily achievable.
>
>You're barking up the wrong tree. A simple high frequency inverter giving the
>required DC output voltage is your best bet.

Since the OP is clearly not a power supply designer, simply buying an
automotive PC supply is probably the best bet. IMO.

Here's an example:
http://www.opussolutions.com/modules.php?name=News&file=article&sid=23

Regards,
Allan

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