DC step-up regulator wiring

I'm using a pololu step-up voltage regulator (http://www.pololu.com/catalog/product/2117) to go from an unregulated battery (VIN line from an Arduino, powered by a 3.7v LiPo cell) to 12V.

No matter what I do, I can't get a voltage to show across the VOUT. There's definitely a voltage applied to VIN, and it's within spec (above the 2.5V minimum for the regulator). The VOUT line just falls rapidly to 0 when I put a meter on it.

Seems like a simple enough circuit. What could I be doing wrong?

EDIT: The circuit below is for the final application. I tried simply supplying 5V on the VIN line to the regulator, and measuring voltage between VOUT and GND, with the same 0 value.

simulate this circuit – Schematic created using CircuitLab

Here's another way I tried to wire it, with the same effect

simulate this circuit

• It would be helpful if you attached a picture of your wiring setup or a schematic of your system. Also, you could just have a bum IC!
– scld
Jul 30 '13 at 18:36
• added schematic... possible that it's a bum circuit, but i've tested two, with the same effect. so - not super likely... Jul 30 '13 at 18:52
• If the attached schematic is not actually what you used to test, then it's the wrong schematic. Simpler is better. Jul 30 '13 at 21:25
• Except that it is. I tested both that one and a direct wiring one, taking power from a 5V regulated wall-wart. Jul 30 '13 at 21:48

The current out of that 754410 is probably not enough to drive the boost converter. I would build the same circuit like so:

simulate this circuit – Schematic created using CircuitLab

And 100 uF may not be enough. You may need 1000 uF! If so, you also want to add a few Ohms of resistance between boost-out and capacitor-plus, to avoid putting too much capacitive load on the boost converter all at once.

• I'll test this out, thanks. It still doesn't answer the second part - why it won't do anything even without any load... thoughts there? Jul 31 '13 at 19:20
• If putting 5V into the regulator gives you 0V out, then the regulator is either broken, or you're using it wrong (forgetting to enable some remote enable pin or whatever.) Aug 1 '13 at 21:04

Some observations:

1. The minimum voltage for the SN754410 (according to a TI datasheet) is 4.5V. You're using the driver outside its normal range if you're feeding it from a 3.7V LiPo.

2. (Gross simplification) Best-case output current for the 754410 is 1A. Assuming perfect 3.7V, 1A output from the driver (which it won't be), that's a theoretical maximum of 3.7W. Assuming your little booster is 80% efficient (which it won't be) that's 2.96W available for your load, or around 246mA for the solenoid. Again, this is assuming lots of ideals - reality will be worse. You didn't specify the DC resistance of the solenoid control winding so I cannot predict how much current it will draw. (\Gross simplification)

3. The regulator should have $33 \mu F$ of capacitance on its input per the web link you cited. It's not shown on your drawing.

4. You haven't mentioned the A-h capacity of your 3.7V LiPo. The Arduino will be eating some of that energy too. A heavy load will likely discharge it fairly quickly - if the boost continues to receive input, it will try and draw more and more current to keep the output regulated (a switching converter shows a negative impedance load to the source.)

• Thanks for #1 - I definitely missed that, and that explains why the driver wasn't putting out anything. Easy fix, I'll just take the 5V rail from the Arduino. The solenoid draws 300mA @ 12V, so ~4W (measured). Jul 30 '13 at 19:46

Power out is always less than power in. Stepping voltage up means you draw a much bigger current at input (in the same ratio).

A Solenoid (even a small one) takes a lot of current. The output from the half H drive is unlikely to be 3V3. To get 1.4A max current out you'll need to put in at least 5 times that. At 3V that's a whopping 7A, I think that rather exceeds the current ratings of the bridge, supply and the regulator.

With any luck your regulator has just shut down until you treat it with more respect.

• the solenoid draws 300mA @ 12V. I expect the ratio to hold, drawing 4x the 3.7V coming off the VIN, so right around 1.2A... Also - I've tried this without the solenoid connected, just supplying VIN + GND to the VIN and GND pins on the regulator, to see what comes out the other side. Still 0. Jul 30 '13 at 19:17