Something like this maybe
Something like this maybe
Hi, all:-
Have a little project that needs to operate off of DC. Any suggestions on the best approach for a wide range (eg. 6V to 60V operation, transients to perhaps 100V) operation?
I only need a watt or so at 5VDC (or +/- 2.5VDC). I'd like to make it idiot-proof, so jumpers and such like are out. Isolation optional, but it might make things easier.
Current-mode flyback to get variable Ton?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
The first thing that leaps to mind is something synchronously rectified
-- essentially a class D amp that you happen to hold mostly at one value for a long time.
But you'd have a lot of loss at 5V if you wanted it to be capable of 100.
-- http://www.wescottdesign.com
On a sunny day (Sun, 15 Mar 2009 07:43:27 -0500) it happened Spehro Pefhany wrote in :
Unless you say somethin gabout what those spikes are, in time duration, it is difficult to say. For very short spikes, a series resistor and transzorb could protect a serial switcher input. For longer duration 'pulses' you need to design for the max voltage, and have a fast enough response time, may work out on L. So: how long is a spike?
Hmmm.. why do I care about synchronous rectification? Diode loss isn't much with a 5V/100mA output. Am I missing something?
50-60% efficiency would be just peachy. Unfortunately, it's more important at ~12V in than 50V. A linear regulator followed by a 6:1 buck regulator would probably do.Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
switcher
The 100V is what gets past the TVS.
Milliseconds.
Looks like a variable frequency current-mode flyback could cut it.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
I suggest a SEPIC design.
Current mode or a variable Ton based on the input voltage seems needed. At low input voltages, the inductor current will almost certainly go continuous. At high input voltages, you would need too much inductance for that.
At the very top of the input voltage range the frequency will need to decrease because the switching circuit will have a minimum on time.
Making the Ton based on a current sense and then basing the off time on the output voltage should give a system that is stable over the full input voltage range.
The SEPIC design can be done without having to get a transformer at all. If you can get an inductor with two windings, off the shelf, I suggest this sort of a thing:
L1 L2A C1 D1 ----)))))-----)))))-----+---!!---+-->!---- ! ! O -)))))--GND / L2B ! GND
L1 is a small inductor. L2 does most of the work. If the L2A and L2B are tightly coupled, C1 can be a modest sized capacitor. D1 needs to be big and fast.
Another way to go may be to build a simple booster that takes the 6V input up to about 20V. When the voltage is above 20V, the transistor in the boost would stay off and the "20V" supply would follow the input. This would make the bucker design a lot easier.
))--GND
L2B
BYou don't mention what your output voltage quality needs to be (ripple voltage etc?).
If it does not need to be short circuit safe, I would use an ultra simple hysteretic buck (no isolation, bang-bang mode). If you need perfect ripple, then set the buck some hundreds of millivolts above the desired output and add a LDO to the output.
Regards
Klaus
Is this for automotive (or similar) use? .
No, not for use in a vehicle.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
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