12V DC to 220V DC Boost Converter Circuit

In this article I have explained a very simple method of acquiring 220V DC from a 12V DC source. The idea utilizes inductor/oscillator based boost topology with the help of the IC 555.

Circuit Operation

Now let us learn more about this simple 12V to 220V DC boost converter circuit, which is built around IC 555, one IRF840 MOSFET, one inductor, and then a few transistor parts for feedback side.

It is made to boost a low 12V DC input into a much higher DC output, somewhere near 220V DC, by fast inductive switching...

555 IC Astable Frequency Generator

If you look at the circuit diagram on the screen, then the left side starts with IC 555 working as an astable oscillator. In that area, R1, R2, C1 decide the switching frequency of the integrated circuit.

IC 555 keeps sending rectangular pulses from pin 3, and that pulse becomes the switching drive for the mosfet.

Pin 8 and pin 4 go to the +12V line, while pin 1 goes to ground. Pin 5 is connected to ground through a 10nF, which helps keep the integrated circuit quiet from switching noise, so it stays stable.

The pulse coming from pin 3 passes through 1k resistor before reaching the gate of IRF840. That resistor limits gate charging current and also saves the output side of IC 555.

1N4148 diode is placed around that gate path, so when the pulse goes low then the gate can discharge faster. Because of that the mosfet turns off quicker and switching loss stays lower.

MOSFET Switching

Now IRF840 is the main switching part here. It turns on and off again and again following the pulse from IC 555. When it turns on, then current starts moving from twelve volt supply through L one and then through the mosfet to ground. During that small on time, L1 stores energy inside its magnetic field.

When the mosfet turns off, then that magnetic field inside L1 collapses and throws a high-voltage reverse pulse.

That pulse appears at the drain side of the mosfet and then goes through the 5 ampere Schottky diode into the output capacitor.

Because this keeps repeating, the capacitor slowly charges and reaches high direct current voltage near two hundred twenty volts.

L1 is the Main Boosting Component

L1 is actually the part doing the voltage BOOSTING work, so its quality matters a lot. A ferrite core inductor works better here. A practical winding can be around forty to forty-five turns of one millimeter copper wire on ferrite rod or ferrite toroid core, which usually gives proper response.

The capacitor here is 100 microfarad rated at 400 volts, and it stores that boosted energy while also smoothing the output side.

Automatic Output Voltage Control

Now let us see the automatic voltage control side also.

At the output, 180K resistor and 10K resistor make a voltage divider. That divided voltage goes to the base of the shown BC547 transistor. This transistor keeps watching output voltage.

If output rises above the set level, then the left BC547 transistor turns on and grounds pin 5 of IC 555, executing PWM control, which limits further voltage rise. The 4.7k preset is there so you can adjust carefully and bring output near two hundred twenty volts.

Automatic Output Overload Protection

Now if we want overload control also, then one current sensing resistor marked RS can be added as shown. When output current increases, then voltage develops across RS and switches the right side BC547 transistor on, which grounds the MOSFET gate.

So now current limiting starts and mosfet gets protection during overload. 100 ohm resistor and 0.1uF capacitor there help steady the sensing action and reduce switching spikes.

We can also see one snubber network across drain and source of the mosfet, made using one 100 ohm and 0.1uF high-voltage capacitor. That part absorbs sharp spikes, so mosfet reliability improves.

This is Only a Low Watt Converter

In practical use, this circuit is only for small high-voltage jobs. Output power usually stays around five watts to fifteen watts, depending on inductor quality, switching frequency, and how strong the input supply is.

Ideally one 7 ampere-hour 12 volt battery or more works better, because weak adapters often fail when sudden current pulses are demanded by L one.

Caution

Please remember, although input is only twelve volts, output reaches dangerous high-voltage direct current. High-voltage direct current can be more dangerous than alternating current, because it does not naturally cross zero, so before touching the circuit always discharge the output capacitor.

Circuit Diagram

WARNING: THIS CIRCUIT INVOLVES HIGH VOLTAGE, EXTREME CAUTION IS ADVISED WHILE HANDLING THIS CIRCUIT.

IC 555 Pinout Details

Audio/Video Representation

How to Calculate all the Parts (For 1 Amp 220V Output)

Let's assume the maximum output current required is 1 Amps.

So 220V * 1A = 220W output.
From 12V battery, ohh so now we see the problem already.

Even if we assume 85% efficiency, which is optimistic, yep a little hopeful.

Pin ≈ 220 / 0.85
≈ 259W

Input current then becomes:

Iin ≈ 259 / 12
≈ 21.5A

So now our inductor L1 and MOSFET must survive that, and if current rises then it must not panic.

Around 25A peak current...
Around 220V drain voltage..

This is not small but maybe possible if parts are seriously selected.

Now duty cycle, which is the main issue here.

For boosting:

D = 1 − (Vin / Vout)
= 1 − (12 / 220)
= 0.945

So now 94.5% duty cycle, which means if duty goes that high then stress also goes high, that is the real heat generation issue here, on the MOSFET.

Now 5555 astable working with 50kHz, let us see.

Formula:

f = 1.44 / ((R1 + 2R2) * C1)

Choose C1 = 1nF.

50000 = 1.44 / ((R1 + 2R2) * 1e-9)

Then:

(R1 + 2R2) ≈ 28.8k

So we take:

R1 = 4.7k
R2 = 12k

Check:

R1 + 2R2 = 4.7k + 24k
= 28.7k

Close enough right... so frequency comes near 50kHz, that looks fine...

Now inductor, which is hugely critical, so lets pay attention here.

Input current ≈ 21.5A.
If ripple is 20%, then ΔI ≈ 4A.

Boost formula:

L = (Vin × D) / (ΔI × f)

L = (12 × 0.945) / (4 × 50000)
L ≈ 56 µH

So L1 equal around 56 µH.
Current rating must be 30A or more.
Use good Ferrite core only, since if core is weak then saturation quickly happens, killing the MOSFET.
DCR very low, below 10 milliohm if possible.

If inductor saturates then MOSFET dies instantly, without warning...

Now MOSFET side.

Ipeak ≈ 21.5 + 2
≈ 23.5A

But if spikes come then you can design for 30A minimum.
Voltage rating should be at least 500V.

IRF840, which does not look good here.
Rds(on) ≈ 0.85Ω.

Loss:

P ≈ I²R
≈ 20² × 0.85
≈ 340W during ON time

Even if duty scaling reduces average, still too much heat, it will overheat badly.

So we need:

500V 30 Amp MOSFET
Rds(on) below 0.3Ω ideally
Big heatsink, not small toy one

If one device struggles then parallel two, but layout must be tight, otherwise sharing goes wrong.

Please Use FQD20N60 or FCPF20N60 for the MOSFET.

Now about the diode.

It must handle 1A average output, but peak pulses go 20–25A.
Reverse rating at least 400V, but safer is 600V.

Ultra-fast diode is mandatory, since if recovery is slow then losses rise.

Schottky diode ultra-fast 600V diode is practical choice.

Now let's check real world situation..

220W from 12V boost is possible, but stressful.
Efficiency maybe 75–85% best case.
Copper tracks must be thick, since if tracks are thin then heating happens.
Cooling must be serious.

Note: This is not a small hobby circuit, it becomes power hardware.

Now Even at 1A output, frequency is not main issue.

The real issue is 94.5% duty cycle.

Only 5.5% OFF time exists, and if energy must transfer in that small window then current spikes grow huge, That can creates high peak currents and heavy switching stress.

That is why industrial designs do not boost 12V straight to 220V in one stage at high power.
They use transformer-based topology, since then stress spreads better.

So now safe recommendation.

With 555 boost style:

220V at 200mA–300mA, around 50W–60W, comfortable zone.
1A, which is 220W, possible but becomes aggressive, so make sure parts must be strong.
Above all that, 1 amp at 220V might not be practical, you will fight MOSFET heating and failure, sorry that is reality.