Hi everyone =) Recently i've stuck with searching a simple, cheap low-voltage PWM controller IC. My requirements were quite clear (and seem to be easy to meet) - operation voltage range (at least) 4-12V, low-side MOSFET driver with (at least) 1A output, adjustable frequency, current-mode control.
It's hard to believe, but almost ALL the IC manufacturers have a BIG TROUBLE making that kind of device!
There is a good and cheap old IC, which meets almost all requirements except low voltage operation - that is UC3845. it is also very cheap, about 10 cents.
There is a lower voltage CMOS version - UCC3805, produced by Texas Instruments/Unitrode. But it's surprisingly expensive, about 10 times (i cant understand why) and seems to be hard to obtain.
There's also LM3478, which is almost ideal for described requirements, with except of high-frequency operation (not less than 100 KHz recommended).
That's everything what i have found.
So i create this thread for other possible finds/additions, which, as usual, could happen unexpectively
Just like in UC38xx family: there is a current sense amplifier (comparator) input, which usually connects to "sense" resistor installed between power MOFET source and circuit ground. Switching current at this point is represented by sawtooth ramp of certain amplitude. When current amplitude crosses comparator threshold, PWM signal is terminated until the end of period.
This allows to keep stored energy (per cycle) in power inductor at constant, wheh supply voltage changes.
Found another one, SIP2800 family, produced by Vishay Siliconix. Seems to be direct replacement of UCC3805 and even pin-compatible. but there are no russian suppliers who has stock of this IC here's what Mouser says about it: mouser.com/ProductDetail/Vishay-Siliconix/SIP2803DY-T1/
found another one: LT3750. but very expensive and seems to quit production soon. there are some interesting features in that IC, like sensing secondary voltage from PRIMARY side (e.g. no voltage feedback needed). datasheet explains how that works. good start to develop custom PWM...
Last Edit: Mar 18, 2017 5:26:59 GMT -8 by lamazoid
Another crazy (actually not) idea: put a service step-up converter before UC3845, to bypass UVLO threshold. I've found some cheapr IC's to implement this, 34063 for example (and it's modern version NCP3063 from ON semiconductor). This should (will) work from as low as 3V supply. Total BOM cost it 2-3 times less than with UCC3805.
Actually i have already tried this approach, with ucc3805 & NCP1402A to run an HV converter off a supercap (2.7V fully charged). I have not measured overall efficiency, but it worked down to 0.8V !
Last Edit: Apr 5, 2017 10:17:56 GMT -8 by lamazoid