I have replaced the 2A inductor with 165 mA inductor. The result I told now was with that. (I thought the 2A inductor drew too much current).

The original inductor only drew as much current as the circuit allowed it to. Changing to an inductor that, presumably, saturates at a lower current won't make the circuit work any better.

 

The original inductor only drew as much current as the circuit allowed it to. Changing to an inductor that, presumably, saturates at a lower current won't make the circuit work any better.

The load resistor is a 100 ohm 2W resistor. Two in series = 200 ohms 4 watt resistor. So could this probably be drawing a high current? ( I am trying hard to figure out which component is drawing this much current)

I also have a single 220 ohm 1/4 W resistor? Is this better to use so as to draw less current from the circuit?

 

Hello,

The power in the 200 Ohms load will be 1/4 of the power 100 Ohms load,
as the current in the 200 Ohms load is 1/2 the current of the 100 Ohms load.

Bertus

 

I am trying hard to figure out which component is drawing this much current

The inductor can draw excessive current if (a) it saturates, reducing its inductance or (b) the 100kHz oscillation fails or is slow to start. Simulation with LTspice shows that a 100uH inductor pulsed properly with 100kHz 67% duty cycle will have ~0.6A current peaks, but if condition a or b applies then the current could be several Amps, limited primarily by the resistance of the inductor. Simulation also shows that voltage spikes of ~280V will be present at the FET drain unless you take steps to suppress them! Is MATLAB showing you similar results?

 

http://www.alliedelec.com/triad-magnetics-rc-10/70218507/

This is more like an inductor you should be using for this project.

 

The inductor can draw excessive current if (a) it saturates, reducing its inductance or (b) the 100kHz oscillation fails or is slow to start. Simulation with LTspice shows that a 100uH inductor pulsed properly with 100kHz 67% duty cycle will have ~0.6A current peaks, but if condition a or b applies then the current could be several Amps, limited primarily by the resistance of the inductor. Simulation also shows that voltage spikes of ~280V will be present at the FET drain unless you take steps to suppress them! Is MATLAB showing you similar results?

Well the peak current across inductor was around the same. I will check and inform you tomorrow. But I did not measure voltage across the drain. I am shocked at the figure! Please tell me something to suppress them. Already I have damaged one mosfet.

 

Already I have damaged one mosfet.

IIRC, you've already been told that you need a snubber diode to supress back EMF.

 

IIRC, you've already been told that you need a snubber diode to supress back EMF.

Yes. I put a snubber diode across Lin and will put one for L and mosfet each. Is it sufficient? 280 Volt spike is so huge.

 

You need to read this

 

You need to read this

Thank you for sending this. Hardware implementation is so much more harder than I thought it would be. But since I am not using a re-lift topology and a normal power MOSFET which requires a drive, I don't need those hardware parts. Feedback control is a must though.

Meanwhile, when I measured the input current drawn by the circuit with a multimeter, it comes to just 1.6 mA with the 9V battery (fully charged battery with an OC voltage of 10.54 Volts). The output current measured comes around 0.5 mA (with which I was able to light 5 led lights in series with a 100 ohm resistor). But I am surprised that 0.5mA is sufficient to light led lights. (Bright light, not dim)

The voltage across MOSFET appears to be 30 Volts (Drain to Source) when measured on a CRO.

 

http://www.alliedelec.com/triad-magnetics-rc-10/70218507/

This is more like an inductor you should be using for this project.

But this inductor also has 0.98 ohms according to spec. From this discussion, I thought that such values of resistances (for inductors) are too high for switching regulators .

 

I believe that is a typo by the seller in the description.
The DATASHEETS number is .098 ohms.



ALWAYS read the datasheet for any part you choose.

 

I believe that is a typo by the seller in the description.
The DATASHEETS number is .098 ohms.



ALWAYS read the datasheet for any part you choose.

OK. I only read the seller description.