Wimpy/current limited boost chip

little boosties chips are so cheap now I'd suck it up and go for that option, don't worry that they're all less "wimpy" than you like. The e.g. MCP1624 has a 0.6 volt startup and outputs 5 volt, it's 35 cents in quantity of 500.

I've tried to shave pennies by rolling my own but except in the simplest situations like say a unregulated charge pump made from a 4000-series oscillator, or 555-timer voltage inverter, "Muntzed" SMPS converters are finicky, they're tough to feel confident enough about to put into something for sale (at least for me), I have almost _never_ been rewarded for taking that approach.

My vote is to just get the cheapest boostie chip with a AA-appropriate startup voltage and suck it up and don't fret it, sorry

if your cheapie boost doesn't have any niceties like user programmable current limit or shutdown but it has a low startup voltage should be able to do the current limit/wimpify it on the input side, something like this maybe:

(probably needs to be a pull-down resistor on the right hand 3904 base)

Diy sm boosters can be very simple, but lack any real protection. In an education environment that is a no-no - and in pretty much every environment. By the time you've added every kind of protection you've wasted time.

NT

Designing electronics for pay should be enjoyable or at least educational, if you can get away with it and get two birds that way. Not always possible but it's an ideal. IMO power supply design is a necessary job but has very little fun involved, and usually isn't particularly educational, either. it's a drag.

Avoiding ill-advised career changes to sales or pushing papers, due to burnout also has financial value, besides just time and parts

Thanks. I have a few days to think about it before I need to make any decisions.

Clifford Heath

Many converters have a fault output, to indicate they can't meet the goal. I went through a bunch of boost converters in 5 and 6-pin SOT-23 packages,* and only one had a fault pin (which could also drive an LED). That was the ISL9111, which also happens to be NRND. Most of them used their extra pin for an enable.

• I didn't look at all the LTC parts, too expensive.

On 07/03/2019 01:05, Clifford Heath wrote:

If high efficiency and low noise high stability output are not needed then a quick and dirty inverting discrete boost can be easy and cheap.

Survives a reversed cell - probably common in schools - and won't pass that reversed polarity on to the payload. Expect to have to fiddle with values and still only get mediocre performance but that may be enough for your target app ...

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SYMBOL diode 208 -32 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 496 -32 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL cap 304 -304 R0 SYMATTR InstName C1

SYMBOL cap 320 160 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 47p SYMBOL res 16 320 R0 SYMATTR InstName R1 SYMATTR Value 100 SYMBOL res 128 96 R0 SYMATTR InstName R2 SYMATTR Value 6800 SYMBOL res 224 32 R0 SYMATTR InstName R3 SYMATTR Value 6800 SYMBOL res 752 -496 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 33 SYMBOL res 816 -432 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1000 SYMBOL res 896 -256 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R6 SYMATTR Value 500 SYMBOL diode 96 -384 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL LED -176 -448 R0 SYMATTR InstName D5 SYMATTR Value NSSWS108T SYMBOL res -176 -288 R0 SYMATTR InstName R7 SYMATTR Value 1000 SYMBOL zener 256 -240 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D6 SYMATTR Value BZX84C8V2LT116 SYMATTR Description Diode SYMATTR Type diode SYMBOL LED 560 -304 R0 SYMATTR InstName D7 SYMATTR Value QTLP690C SYMBOL res 560 256 R0 SYMATTR InstName R8 SYMATTR Value 100 TEXT 644 410 Left 2 !.tran 20m TEXT -104 -448 Left 2 ;GRN=RUNNING TEXT 592 -200 Left 2 ;RED=OVERLOAD TEXT 800 -264 Left 2 ;LOAD TEXT 632 -24 Left 2 ;EPW MAR 2019 TEXT 632 96 Left 2 ;FOR CLIFFORD HEATH SED TEXT 632 32 Left 2 ;MINIPOWER BOOST

piglet

A microcontroller boost

Operate micro directly from 1.8V

Use external logic level FET with inductor and boost diode

Add source resistor to monitor the current

Cheers

Klaus

Nice, something like that may indeed be enough. It seems to work nicely, after I fixed up small copy/paste errors :)

Clifford Heath.

Unfortunately that costs more than my budget for a complete module. But thanks for the info, I can stop dreaming.

Clifford Heath

I don't have 1.8V. Should run from 1.2-1.5V. The MSP430L092 would work, it's ok at 0.9V and has a brownout detector.

Parallel some port pins and no external FET would be needed. Unsure what happens to it (running off the battery) when the FET shorts the battery to ground via the inductor. I guess a big enough cap would allow it to survive.

At $0.95/2000 it might still be a challenge to get it under $1.50, but getting close.

Clifford Heath.

the port pins would rise in V to output plus a volt or so. I think you'll need a tr. Could you use switched C boost instead?

NT

Or a single open-drain gate. But I suspect paralleled port pins would be enough. I need to look into the drain resistance at a low Vdd.

Difficult to get 9V from 1.2V after diode drops.

Clifford Heath.

Yeah. I'm imagining relays clacking away :)

NT