Any recommendations on a good, small switcher to go from 27volts to 5 volts @ 100ma.
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Take a look at:
Are you looking for a point of load converter board or a switcher device such that you can design your own switcher?
If you want a POL stick, search google for Point of load converters.
If designing your own switcher will the input voltage vary significantly and will the output current vary significantly? (Significant is a ratio of at 2:1 or more).
If the input voltage varies but the output current does not, choose a current mode controller. If the output current varies but the input voltage does not, choose a voltage mode converter. If both vary, try a voltage mode converter that has feedforward compensation to make the device insensitive to input voltage variations (the LTC3703-5 is one, although it's rated for higher currents).
The general rule for the loop compensation is: Voltage mode converters are sensitive to Vi/Vo variations (and for a fixed output that means just Vin) and insensitive to Io variations. Current mode converters are sensitive to effective Ro variations (Vo/Io, so for a fixed voltage output current variations) and insensitive to input voltage variations. Obviously, both are sensitive to Vo/Vi as it sets the main switch duty cycle but at your range that's not an issue. (Lower than 10% and higher than 90% can limit your choices)
Cheers
PeteS
Looking for a way to power a very small pic processor and a couple of optos from 18-30 vdc. Was looking at a LM2936MP-5.0 but 50 ma may be cutting it close.
Richard
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I would suggest one of the wide range of Linear Tech current mode controllers. Get one rated at least 36V (a little headroom helps).
Go to
At the next page select (from the drop down box)'High Input Voltage' , then 'View category'
At the next page, select 'View table'
You'll see a whole list of devices that would suit your needs for Vin and Iout. Monolithic means the switch is internal (so all you need to provide is the external schottkys, caps and a small inductor) [I'm not trying to teach you basics, just trying to be complete]
There are a number of devices there that should meet your needs, *and* happen to be easily available from your favourite mail order parts company.
Cheers
PeteS
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