RE: TI-H: ti-calc schematics...

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RE: TI-H: ti-calc schematics...

Grant,

You have to be careful when you buy inexpensive switchers (DC to DC convertors).  Some are constant duty cycle convertors that require a regulated input, and provide an output voltage that is a fixed ratio of the input.  If your input varies from 4V to 6V (5V +/- 20%) then your output will vary 20%.

The better switchers have feedback that varies the duty cycle in response to variations in the input, maintaining a constant output voltage.

The equation you start with when designing a switcher is:

Vout = Vin (duty cycle)(transformer turns ratio)(efficiency)

If efficiency is constant (not quite true but close enough for this discussion); and Vout, turns ratio, and Vout are constants, and Vin varies, you must change the duty cycle to resolve the equation.  The only other way is to fix the duty cycle so the output is too high then add a linear regulator.  You get a clean output but efficiency drops, which kills battery life.

There are three options:

Unregulated Switcher:  Cheap and efficient but poor performance if Vin is not regulated
Unregulated Switcher with Linear Regulator: Moderate expense, worst efficiency
Regulated Switcher: More expensive and less efficient but great performance

I used to work at Interpoint designing switchers (www.interpoint.com) before getting into RF, and they have some good application notes.  Their power products target high-end military and space applications, so their products are not accessible to hobbyists, but their app notes can help you understand the technology and make selecting a switcher easier.

Mike

-----Original Message-----
From:	Grant Stockly [SMTP:gussie@alaska.net]
Sent:	Monday, July 13, 1998 10:54 AM
To:	ti-hardware@lists.ticalc.org
Subject:	Re: TI-H: ti-calc schematics...


6 to 6
5 to 6
4 to 6

It makes it so that the calc gets a constant voltage.

>Changing from what to 6V?  What's the purpose of the conversion?
>
>
>On Mon, 13 Jul 1998, Grant Stockly wrote:
>
>>
>> No voltage change.  a DC to DC 6v converter.
>>
>> >Why would the voltage change?
>> >
>> >
>> >
>> >
>> >> Thats why I stated to get a DC to DC converter so the voltage stays the
>> >> same.  I think ALL ELECTRONICS had one for $3.
>> >>
>> >> ---
>> >>
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>> >> To talk to me direct, I'm 'weridguy' on AOL IM service.  I don't have an
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>> >>
>> >> Thanks.
>> >>
>> >>
>> >>
>>
>>
>> ---
>>
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>>
>> Thanks.
>>
>>
>>


---

To Subscribe to the ACplay mailing list, please send a message to
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To get an e-mail every time http://gussie.alaska.net is updated, please
send a message to gussie@alaska.net with the subject "SUBSCRIBE ACNOTIFY".

To talk to me direct, I'm 'weridguy' on AOL IM service.  I don't have an
AOL account, just the IM thing.

Thanks.
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