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Boost converter Circuit

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gauravkothari23

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Hi all,
i a trying to make a boost converter using 555 IC.(Circuit diagram attached).
My problem is the mosfet attached IRLML2402 burns out instantly as i connect the power to input 5V. so i tried using IRF540N, but even this mosfet gets hot withing a second and but i get output voltage of approx 15V.
can anybody please let me know what the problem is.
 

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  • Boost.png
    Boost.png
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Several things:

The gate storage in the MOSFET will be too long to be efficient - drop R2 to about 100R.
D3 needs to be a fast switching device, the 1N4007 is useless at more than a few hundred Hz.
The frequency is probably too high, for that kind of circuit and components, aim for about 25KHz to 50KHz.

Brian.
 

Most Mosfets Require 10 Volts on the Gate to Fully Turn On.
So you should be using 12 Volts in.
Also Mosfets Require Heat Sinks, to help prevent Over Heating.
Use a HF4007 or similar for Faster Switching.
 

Hi,

Without load the output voltage is not determined and may become very high. Too high for the MOSFET.

Klaus
 

I Can't find a Rating on that IMRL2402.
An IRF540 is a Bit Low in Voltage for this circuit.
An IRF640 or an IRF740 Would be More Suitable.

Depending on the Q and Current rating of the Choke, Output voltage will be Several Hundred Volts.
No Load, Possibly 400 or more.
 

also , how is your layout?...maybe the attached helps you in smps layout.
But also you may as well just use a boost controller, or a current mode controller...what about you try the HV9910B ,as its easy to implement for a low power boost...just have a potential divider feeding into the internal comparator.

- - - Updated - - -

you also need an input capacitor, and a cap near the controller as it will be needed to supply the pulsey gate current

- - - Updated - - -

1....keep switching power current loops as low in area as possible
2...try to avoid drawing switching pulse currents through lengths of control ground as it will cause ground bounce, and noise problems for you

- - - Updated - - -

also, you have no source sense resistor, and you need that...but the 555 gives you no comparator into which you can put its signal., so i beg you to use the hv9910b, or the uc2843 etc etc

- - - Updated - - -

so by "having a go", yes , you have no doubt learnt much.

- - - Updated - - -

well done!
 

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  • Basics of SMPS Layout _4.doc
    645.5 KB · Views: 71

Hi,

Posting to uselessly/usefully add: take a look at gate drive app notes and circuit ideas if it will add anything to the circuit once above recommendations are carried out.

This is a nice enough one, by Laszlo Balogh, the schematics are around pages 15 onwards if you want to skip to the point for ideas (and then read the salient info.): **broken link removed**
 

Not Very well Drawn, But the Circuit in Post-1 Will Work.
However the Supply Voltage should be 10 to 12 Volts.
R2 should be 100 to150 Ohms.
L1 should be a High Q, 100uH High Current Choke rated at 2 amps or more.
The 1N4007 Will work but a HF4007 or Other High Speed diodes are Better.
 

..yes the Balogh one above is a great one on gate driving.
Look at your miller plateau (Balogh shows it in the above)....the plateau is where most of you switching loss happens....the plateau is where the drain transitions from high voltage to low voltage or vice versa.
 

Not Very well Drawn, But the Circuit in Post-1 Will Work.
However the Supply Voltage should be 10 to 12 Volts.
R2 should be 100 to150 Ohms.
L1 should be a High Q, 100uH High Current Choke rated at 2 amps or more.
The 1N4007 Will work but a HF4007 or Other High Speed diodes are Better.

thank you all for your reply.
i cannot source 10 to 12V, because the input itself it 5V and output what i need is around 8V, where input current is approx 1.5 Amps and output load current is around 700 mA.
so, how can i avoid the output voltage to boost more than 8V.

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Hi,

Without load the output voltage is not determined and may become very high. Too high for the MOSFET.

Klaus

cannot i stable the output voltage by adjusting the duty cycle of mosfet.
 

IRML2402 is a "logic level" MOSFET with 0.7V Vgs,th, it can well work with 5V input. It's current handling capability is however too low for the intended load.

cannot i stable the output voltage by adjusting the duty cycle of mosfet.
Yes, but the circuit has no means for it, except a manual duty cycle adjustment. It may work if you have a constant load, e.g. a resistor. Below a certain output current, the converter operation transits to DCM (discontinuous conduction mode) and the duty cycle has to be varied with the load. For open output, the duty cycle needs to go down to about zero. Usual boost converters have a voltage regulation loop controlling the duty cycle.
 

Hi,

so, how can i avoid the output voltage to boost more than 8V.
You need an output voltage feedback and a (fast enough) regulation loop.

Otherwise you need to install a high power zener that disspates all the power that is not used by the load.

May I ask why you don´t use a ready to buy step up regulator IC (boost regulator IC)?
There are many hundred different ones from various manufacturers. All come with compact - less part count - design, all including voltage regulation and other safety features: like short circuit protection....

I personally won´t waste that much time and money to design it using NE555....

Klaus
 

Hi,


You need an output voltage feedback and a (fast enough) regulation loop.

Otherwise you need to install a high power zener that disspates all the power that is not used by the load.

May I ask why you don´t use a ready to buy step up regulator IC (boost regulator IC)?
There are many hundred different ones from various manufacturers. All come with compact - less part count - design, all including voltage regulation and other safety features: like short circuit protection....

I personally won´t waste that much time and money to design it using NE555....

Klaus

i want to built my own because of cost factor. here i india we get the boost converter module or any related IC's at around 2 US $, which are quite expensive, i am planning to build the same in half a dollar using NE555. and the thing is i dont need a sample of piece. i need the same in some hundreds. so i am planning to develop the same.

I tried the same using zener diode, so i am getting fixed output voltage, but when the input voltage drops, the outputs also drops.
 

Gauravkothari23, the point people are making is that there is nothing to stabilize the voltage. If you want a stable output you need a feedback system, one that monitors the output voltage and adjusts the on/off ratio automatically to keep it stable. At the moment, you would have to manually adjust the potentiometer all the time as the voltage changes, I'm guessing that is impractical. By the time you have added all the components to do that around a 555 it would be cheaper and certainly more efficient to change to a dedicated IC like the ones suggested.

Brian.
 

Hi,

here i india we get the boost converter module or any related IC's at around 2 US $
I didn´t talk about a "module" but about an IC, which should be much cheaper than a module.

For your cost calculation you have to consider:
* development cost (consider a realistic money/hour rate for your job)
* part count
* board space
* assembling cost
* additional features
* and others (like fails during development, during overcurrent situations in the field....)

In Europe I can´t imagine a discrete NE555 solution to be cheaper than using a dedicated controller IC with integrated control loop, oscillator, overcurrent protection, undervoltage protection, voltage reference, soft start, driver and MOSFET.

I tried the same using zener diode, so i am getting fixed output voltage, but when the input voltage drops, the outputs also drops.
--> expectable without control loop.
Note: You didn´t mention variable input voltage before. --> another call for a suitable control loop

*****
BTW: your design is missing a suitable input capacitor.

Klaus
 

Hi,

I want to add my penny to Klaus' comments, to be helpfully realistic, I in no way wish to offend at all... Most of the websites I see that make this kind of circuit (or similar) with 555s are doubtfully vague or outright low on fact and high on self-publicing vanity, oh - and the comments tend to be filled with (sic) "I can't get this to work". Don't believe the hype, friend, check real resources by semiconductor manufacturers. I wouldn't buy that.

Notice the insistent repetition by experienced engineers of the term control loop and how you can get e.g. 8-pin controllers that would substitute the 555 and reduce the cost of what you'll end up having to add to the "Christmas tree converter" just for it to work correctly...

Good luck!
 

You need a zener (7v5) from the output feeding an npn xtor via a 1k res, with 1k from base to emitter (gnd) the collector goes to pin 5, put 100nF on pin 5 for a soft start.

the above will regulate the output volts to ~ 8v5, D1,2 should be 4448's, R1 -> 2k2, RV3 -> 5k, C3 -> 4n7, put 10uF pin 8 to gnd, D3 should be a schottky 40V 1A,

good luck ...
 

the input itself it 5V and output what i need is around 8V, where input current is approx 1.5 Amps and output load current is around 700 mA.

As an alternative this voltage doubler is based on a full H-bridge and two capacitors. Since you mentioned a 555 IC then that is handy for producing bias pulses. The 5V supply has a reasonably smooth current waveform drawn.

555 IC drives H-bridge doubler 2 caps 5V to 8V 11 ohms.png

By adjusting resistor values you can obtain output approaching 10V. It's optional to add zener regulation and/or limiting safeguards.

The output is not referenced to ground. If you wish it referenced to ground then you need a different voltage doubler topology.
 

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