Boost converter

Question

Hi,I am a beginner in electronics and i just wanted to help with a certain circuit of mine that I was handling and it was a boost converter but the input 3.7v is the same as the output and wanted the output to be 5v DC 
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kkazem · Answer

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.

robogary · Answer

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.

kkazem · Answer

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.

Boost converter

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