I tried to make a simple boost converter circuit for driving an LED using 555 timer IC, but somehow the output voltage is not increased at all. I suppose that the problem is the inductor I used, since I was unable to find a suitable one (i.e. around 220uH) and I end up using a 33uH.

Can somebody help me to build a 220uH inductor, or help me find a solution regarding the boost converter not boosting?

I am supposed to give around 3V input and get at least 12V output.

The components I used are:
555 IC
100uF 25V capacitor
1N4007 diode
10k variable resistor
33uH inductor


Schematic source: Et Discover

The circuit diagram used is this. Also note that I used a 20nF capacitor with the 555 IC which, according to diagram, should be 100nF. Is this the problem or the inductor as mentioned?

  • 3
    \$\begingroup\$ Can you provide a circuit diagram? Each part should have a reference designator (e.g. R1, C1 etc) and value. Without this I don't see how we can help. Also what frequency are you switching at a 1N4007 would be too slow for normal switching frequencies. \$\endgroup\$ Commented Nov 25, 2019 at 15:56
  • 2
    \$\begingroup\$ I suppose that the problem is the inductor i used since i was unable to find a suitable one(i.e. around 220uH) and I end up using a 33uH. This wouldn't cause your boost converter to "not work" but perhaps not work the way you want it to. Yes, as Warren mentioned, please provide a schematic. Also, it would be helpful to also list some other specifications as well, not just your desired output voltage, i.e. ripple, switching frequency, etc. You've chosen a particular FET and some other components, which indicate that you are looking for more than just a 12v output. \$\endgroup\$
    – user103380
    Commented Nov 25, 2019 at 16:03
  • 1
    \$\begingroup\$ Are you sure that the NE555 can work properly with such a low input voltage (3V)? \$\endgroup\$
    – G36
    Commented Nov 25, 2019 at 16:31
  • \$\begingroup\$ Yes! I suppose. What should be minimum voltage required according to you? \$\endgroup\$
    – user236938
    Commented Nov 25, 2019 at 16:32
  • 2
    \$\begingroup\$ 4.5V according to the datasheet. \$\endgroup\$
    – G36
    Commented Nov 25, 2019 at 16:38

2 Answers 2


At about 5kHz your frequency is too low. Aim for about 50kHz. The circuit below has a timing capacitor of 1nF.

If you move your pot to the position shown below then you can vary the mark without altering the space.

7555 has minimum supply voltage of 2V. 7555 is the CMOS low power version of the NE555.

Diode should be a 1N5819 (Schottky diode) for fast switching and low dissipation because of its smaller forward voltage drop.

Also that's the symbol for p channel mosfet in your circuit diagram. See how the body diode would clamp the output voltage to 0.7V.

Boost Regulator


I believe your only problem is the Gate voltage and choice of FET Vgs(th)

This FET you chose is a standard Vt=2~4V FET which means that a 3V gate voltage barely starts conduction.

You need a gate voltage of about 3x the threshold such as 10V which is used to define RdsOn.

You choice is to somehow use the output voltage to bootstrap the output voltage to the gate voltage of your NPN switch that drives the gate with a diode +Cap or choose a FET with Vt=Vgs(th)<=1V.

The choice of a 555 is a bad one with output voltages.

Normally when using NPN complementary half-bridge drivers the lower PWM switch feeds a diode+Cap to boost the gate voltage for the FET. Here is somewhat similar if using 3V for the 555. OK ?? any questions?


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