I solicited suggestions for a converter which would meet all of the 
following without alteration (regardless of why it may be a good idea 
to alter them)

>> - will accept input from 4 alkaline cells over 6.5v to 4v range and
>> - provide 5 volts output
>> - at a few mA.
>> - Regulation for load or input voltage need not be flash - probably
>> +/- 0.25v OK but I'd expect we could do better.
>> - Efficiency not a major issue. 60% would do! - rather better
>> expected.
>> Probably through hole construction / ie DIP package if ICs used.

As output current is a few mA (say 5 mA max) the quiescent current 
needs to be low to achieve OK efficiency. ie parts that draw 3 mA 
quiescent aren't really acceptable.

Low manufactured cost is a key factor but possibly not originally 
mentioned.

There were various suggestions.
At present I'm looking at either a TL499 design or one based on a 
CD40106 hex Schmitt trigger plus a few transistors. It has a high 
parts count but excellent performance and component cost is low.

Various self oscillating transistor designs proved less than ideal for 
various reasons. (Voltage range, efficiency at low load current, 
startability, ...). (I'm sure a fully transistor based design could do 
a good job with refinement but the 40106 design is not a lot dearer 
and very effective). CD40106 is about $US0.15/1000 Digikey and TL499 
is about $US0.45/1000 Digikey. TL499 has a nasty high current mode 
when the power supply rises slowly - not mentioned in any data sheet 
or app note (of course).

The TL499 is very old but an effective solution. Much more modern 
boost converter ICs exist but they are usually much dearer. Most 
suitable Maxim parts are more like $2/1000 or more from Digikey. The 
LM2578/LM3578 is cheaper (about $US0.50) but not in DIP.

Has anyone got any other suggested IC that may do the job that is also 
well priced - probably not over $US0.50/1000 quantity. Anything this 
'dear' would want a minimum of 'glue' components.



        RM 

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