Boost converter

Hi,

The minimum voltage for proper function of the 555 timer is 4.5 Volts. 3.7 Volts is probably not enough to make this circuit work properly. Even the schematic indicates 5 volts as a minimum voltage. There are circuits designed for 3.7 to 5 volts. You could perhaps salvage one from an old supplemental cell phone recharging battery.

John

Big kudos to you for building a voltage boost circuit.  Its alot of work in designing and troubleshooting. The 555 is a classic multipurpose device.

As another viewpoint, another way to bump up some volts is using a DC DC switching power supply converter

for example https://www.ebay.com/itm/402847203332?hash=item5dcb908004:g:wY4AAOSw39dgn5rC

( I am not promoting Ebay or this seller, just providing an example of an inexpensive solution for boosting voltages from bulk or battery power supplys )

There are inexpensive buck supplies, buck - boost supplies, for low currents to 3 to 5 amps.

Am I missing something here? In the image, I see a wired-in-the-air breadboarded circuit with no 555 timer IC and a very light schematic that really isn't very readable. But I don't see any 555 timer IC. Where is the 555 that I'm not seeing?

Anyway, problem solved. Simply change the IC from an LM555 (bipolar) to a TLC555 (bicmos) which operates down to 2VDC. If all else is OK and you get boosting at 5 VDC in, then this circuit should work and it's an easy fix. The TLC555CN is the commercial temp version, but I recommend looking at the datasheet and getting the best version for your application. 

I simulated the TLC555 boost converter ckt I mentioned using LTSPICE XVII at 2.7 VDC input and it gave 5.2 VDC out. I didn't optimize the pulse width nor did I put in a regulation feedback loop and it runs open-loop with a fixed pulse width in this version. But it can easily be done by modulating the CONT pin (pin-5) with an opamp as an error amp along with a dc reference.

If you look below at the waveforms, the red trace is the DC output of about 5.2V with some ripple. The Green is the bottom-side of the inductor (also the FET drain). The FET I chose here was one with a low enough Vth to make the ckt work at the low VIn of 2.7 VDC. I wouldn't try to build this ckt with that FET. Instead, choose a good, low Vth and low RDSon N-CH FET if you want to build this. 

I got the SPICE model of the CMOS 555 timer IC, TLC555 from the TI website. Just Google TLC555 SPICE model and you'll find it. I had no convergence problems with this IC model, it seemed to simulate pretty well and fast.