Electronic Engineering

[Ned Storm]

Kind of a funny topic to post here but I spent a good proportion of my life focused on this topic and ended up specializing in Switched-Mode Power Supplies like you get inside your PC to convert the mains voltage to 5V, 12V etc.

So if you have any questions on how to bias a transistor, choose your wire or wind a transformer, post here

I got really into optimizing the design of SMPS transformers and now I am optimizing web sites, go figure. We all need our passions right?

Heck, I may as well spill the beans on how to bias a transistor.

So lets start with an NPN high gain transistor.

What we need to do is minimize the effects of the Vbe drift with temperature, so our emitter to ground voltage drop needs to be as large as possible i.e. at least 1 volt. To increase AC gain we can always connect a capacitor across this resistor.

The base should be biased with a potential divider to set the collector voltage at the required level which is the +ve rail minus the emitter voltage + the VCE max and subtract this for the rail and divide by 2 to get a figure to subtract from the +ve rail to get the collector voltage bias point.

Then we can AC couple a signal into the base via a capacitor.

Then, to extract the amplified signal we connect a resistor from the positive supply line to the collector of the transistor so the DC bias point is mid-way between the output signal voltage swings and finally AC couple our signal out of the circuit via a nice big electrolytic capacitor.

OMG - now I know why I didn't create an electronics based website.

p.s. remember to match your impedances well i.e. drive low into high to minimize distortion.

[stu]

Hi

I started in electrical and electronic engineering when i first left school, i did a OND, HND and a few city & guilds then i ended up fixing tv's for about 3 years.

[Ned Storm]

It's funny isn't it, that when people know you are an electronics engineer, they bring you their busted TV's etc. to fix?

The old-style TV's were really horrible to work on with all the grime inside them because of the static attracting dust and moisture. And did you ever knock the RGB driver board at the end of the tube neck and crack the glass to render the TV useless?

But at least we could sometimes fix them, now the modern electronics has to be thrown away if it stops working under warranty. There is no way to find the faults without a lab and a service manual.

[stu]

ya they where a pain with all the muck, i just used to used comperssed air to clean them first, otherwise you just couldnt see what your were doing.

Ya the board on the back of the tube. the tv's where that big to move on your bench you had to lean right over the tv to turn it and without the back on you always caught the bloody board. i had that many tho that where unfixable for other reason i had a few spur tubes around that sometimes fitted.

The worsed thing to fix was dry joints. finding them was so time comsuming at times it wasn't worth trying.

when the brought flat screens out they just became unfixable, i use to like fixing video players, that was always a fun job. not that anyone has them now. my kids wouldn't even know what one was. years ago they use to be so expensive.

[Ned Storm]

Stu, it seems like you had some similar experiences to me only more so

Oh, the dry joints, actually, they tended to be cracked solder joints due to the expansion and contraction due to hot parts.

My latest waste of time electrical repair was replacing a florescent wall light which was perfectly fine except that another wall switch was turned off. 2 hours or more wasted fixing that when I could have simply flicked a switch!

The lesson to learn is to ask more questions.

[Harrison jess]

hey ...
i am running my dvd rom and hdd on another supply and bought a new supply which is 450 volts , but the recommended one is 475 will it work ?

[stu]

(11-01-2010 05:49 PM)Harrison jess Wrote:  hey ...
i am running my dvd rom and hdd on another supply and bought a new supply which is 450 volts , but the recommended one is 475 will it work ?

hi

yes it will work, as with most things manufactured you have a 10% tollarance on what the recomended is.

[jeanbosh]

Electronic engineering is a branch of engineering, research and application involving a variety of technical equipment and the application of electrical components. These components include tubes, such as diodes, transistors and integrated circuits. Disciplines, they are used to design all kinds of things, such as circuit boards and other wide range of electronic applications.