MAGIC of knowledge
I turned the switch on and BOOM! That noise, the tiny puff of smoke and the accompanying smell had become far too familiar.
I looked on in confusion at all the failed electronics components in front of me. I needed answers. Why did the H-bridge circuit not work as “claimed”? Books showed numerous such circuits. The Internet was not short of designs either. They were all similar though. I had done my research. I thought I understood the principles and modalities of operation. Then, where did the fault lie? Frustration was creeping in. But I just had to find the fault and fix it.
I wanted to make the SMPS based inverter because I could learn so much in a field completely new to me and then use the inverter at home during power cuts. In that one night of experimentation, I had failed repeatedly, damaging 24 IR2110’s and a lot more components. I had applied all I had learned thus far. Success, however, eluded me.
After repeated failures, I posted my problem on online electronics forums. Numerous members from around the world, engineers and non-engineers alike, joined in to contribute. I learnt and questioned. Heated discussions, arguments and counter-arguments took place. And I absorbed all I could. I did not get a direct solution to my problem but I felt I had become richer and perhaps, through discussion, helped make others richer.
I spent hours reading documents and application notes, analyzing existing designs and testing the different concepts experimentally. However, the result was the same.
One day I stumbled upon a circuit on the internet, which had a different type of MOSFET gate protection, which employed a resistor between “gate” and “source”. Theoretically this resistor was not required. I redesigned the entire circuit with these resistors connected.
MAGIC! I got the required AC output. No BOOM, no smoke, no smell! 4 resistors (one between gate and source of each MOSFET) that, in total, cost less than $0.25, had been the difference! This was the magic of knowledge – the power of knowledge people refer to.
I then resorted to books and the Internet and learnt why the gate-to-source resistor stopped the MOSFET, and in turn the driver IR2110, from “blowing”.
After completing my inverter, I regularly posted on online electronics forums, especially www.edaboard.com – in the time I found between school, sports, electronics endeavors and other activities – to help others and to learn.
Many people later posted on www.edaboard.com regarding problems where the MOSFET and driver “blew”. I had been the one to suggest the use of the “gate-to-source” resistor and this had been the solution to most such problems.
My repeated failures had frustrated me, but also pushed me beyond the boundary of books to learn, acquire and share knowledge, to believe in the power of knowledge but most importantly to believe in myself and my capabilities. This belief and these teachings helped me in later endeavors to overcome obstacles in my way and achieve success.
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Importance of the gate-to-source resistor:
It prevents accidental turn on of the MOSFET by external noise usually at startup when the gate is floating. The MOSFET may sometimes turn on with a floating gate because of the internal drain to gate "Miller" capacitance. A gate to source resistor acts as a pull-down to ensure a low level for the MOSFET. I have had MOSFETs blowing up in high voltage circuits, without the resistor in place. In most of the commercial power supplies / inverters I have seen, there is a 1k resistor used.
A similar experience is narrated in Sanajaya Maniktala's "Switching Power Supplies A to Z". This is also talked of in Raymond Mack's "Switching Power Supplies Demystified".
I looked on in confusion at all the failed electronics components in front of me. I needed answers. Why did the H-bridge circuit not work as “claimed”? Books showed numerous such circuits. The Internet was not short of designs either. They were all similar though. I had done my research. I thought I understood the principles and modalities of operation. Then, where did the fault lie? Frustration was creeping in. But I just had to find the fault and fix it.
I wanted to make the SMPS based inverter because I could learn so much in a field completely new to me and then use the inverter at home during power cuts. In that one night of experimentation, I had failed repeatedly, damaging 24 IR2110’s and a lot more components. I had applied all I had learned thus far. Success, however, eluded me.
After repeated failures, I posted my problem on online electronics forums. Numerous members from around the world, engineers and non-engineers alike, joined in to contribute. I learnt and questioned. Heated discussions, arguments and counter-arguments took place. And I absorbed all I could. I did not get a direct solution to my problem but I felt I had become richer and perhaps, through discussion, helped make others richer.
I spent hours reading documents and application notes, analyzing existing designs and testing the different concepts experimentally. However, the result was the same.
One day I stumbled upon a circuit on the internet, which had a different type of MOSFET gate protection, which employed a resistor between “gate” and “source”. Theoretically this resistor was not required. I redesigned the entire circuit with these resistors connected.
MAGIC! I got the required AC output. No BOOM, no smoke, no smell! 4 resistors (one between gate and source of each MOSFET) that, in total, cost less than $0.25, had been the difference! This was the magic of knowledge – the power of knowledge people refer to.
I then resorted to books and the Internet and learnt why the gate-to-source resistor stopped the MOSFET, and in turn the driver IR2110, from “blowing”.
After completing my inverter, I regularly posted on online electronics forums, especially www.edaboard.com – in the time I found between school, sports, electronics endeavors and other activities – to help others and to learn.
Many people later posted on www.edaboard.com regarding problems where the MOSFET and driver “blew”. I had been the one to suggest the use of the “gate-to-source” resistor and this had been the solution to most such problems.
My repeated failures had frustrated me, but also pushed me beyond the boundary of books to learn, acquire and share knowledge, to believe in the power of knowledge but most importantly to believe in myself and my capabilities. This belief and these teachings helped me in later endeavors to overcome obstacles in my way and achieve success.
---------------------------------------------------------------------------------------------------------------------
Importance of the gate-to-source resistor:
It prevents accidental turn on of the MOSFET by external noise usually at startup when the gate is floating. The MOSFET may sometimes turn on with a floating gate because of the internal drain to gate "Miller" capacitance. A gate to source resistor acts as a pull-down to ensure a low level for the MOSFET. I have had MOSFETs blowing up in high voltage circuits, without the resistor in place. In most of the commercial power supplies / inverters I have seen, there is a 1k resistor used.
A similar experience is narrated in Sanajaya Maniktala's "Switching Power Supplies A to Z". This is also talked of in Raymond Mack's "Switching Power Supplies Demystified".
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