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Over Voltage rating on transistors, is this called biasing?

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Hi,

Yes that could be one artifact but it would be better if you found a simple circuit that you were interested in that required some sort of bias, and then we could discuss that. That would give you a better idea i think.
 
For a single transistor:
If the positive AND the negative cycles are clipped the same amount then the level is too high, not the biasing.
If a transistor is biased too high or is biased too low then one cycle will be clipped more than the other cycle.
 
If the positive AND the negative cycles are clipped the same amount then the level is too high, not the biasing
.

Level? you mean DC offset voltage is to high?

For a single transistor:
If the positive AND the negative cycles are clipped the same amount then the level is too high, not the biasing.
If a transistor is biased too high or is biased too low then one cycle will be clipped more than the other cycle.

What about for a push pull , like a power amp?

When biasing a push pull , the zero crossing has the transistors OFF TIME

This is also biasing: Not sure what the name is for this type of biasing
There is trim pots which i don't know what the name's are, but they adjust the GAP of the push pull OFF TIME , so the GAP Transistors OFF TIME between the positive and negative cycles
 
If you bias it to work in a normal circuit, then you want to bias it so that the transistor works at some particular operating point which you deem to be a good operating point

Yes the transistor is biased at the Operating point, but the VCC is over the Max rate from the datasheets

The VCC voltage sets up a "bias" for the Collect and emitter right?

When you put a DC voltage higher on the VCC than the Max rating for the transistor , Isn't this over biasing it?

For operation in what is called the 'linear' range'

The Transistors are in the linear range, But the company just puts a higher VCC than the datasheets so the transistor will saturate or give a warm sound

If you pull a squarewaveform function generator , you will see the Corners of the squarewaveform rounded , thats how they test the power amps

I don't know what this is called when you put a higher VCC voltage on the transistor , i thought it was biasing

The data sheet will often show a range of collector to emitter voltage ratings; Vceo, Vcer, Vcex, Vce sus, and all these parameters are for the maximum voltage between collector and emitter

Yes I know, The VCC DC voltage I thought was called Biasing the transistor, but what is it called? the VCC does what to the transistor?
 
I will not bother to copy and post here my replies to these same questions on the other website forum.
 
Level? you mean DC offset voltage is too high?
If the positive AND the negative cycles are clipped the same amount then the level of the AC signal is too high, not the biasing.

What about for a push pull , like a power amp?
The output transistors of a push-pull audio amplifier have their idle current biased a little in class-AB to avoid crossover distortion.

When biasing a push pull , the zero crossing has the transistors OFF TIME
A class-B amplifier has OFF TIME which causes crossover distortion so it is not used for audio or video.

This is also biasing: Not sure what the name is for this type of biasing:
There is trim pots which i don't know what the name's are, but they adjust the GAP of the push pull OFF TIME , so the GAP Transistors OFF TIME between the positive and negative cycles
The trimpot adjusts the amount of class-AB idle current to eliminate crossover distortion. The idle current is fairly low.
 
Thanks for the help

If the positive AND the negative cycles are clipped the same amount then the level of the AC signal is too high, not the biasing.

What do you mean by the LEVEL of the AC signal is too high

Do you mean the Peak to Peak AC voltage going INTO the power amp stage is getting Clipped before the power amps input
 
Transistors can also be operated in 'avalanche' mode, using higher Vce's than the datasheet recommends.

Used as very fast, high current switch, eg: pulsed semiconductor lasers.
 
Ok, let me inject my 2 cents worth.
First, if you supply more VCC than a transistor can handle, you won't "FRY IT" the first time you turn it on. That is the 'breakdown' voltage of the PN junction. Once you go over this value, the 'junction' becomes a zener.... you are doing the same thing a zener diode does. You operate them in the region of their reverse breakdown voltage, AND you need a resistor to limit the current through the zener. The same phenom occurs in a transistor, as it's just a fancy set of diodes. When you go over the breakdown voltage, the PN starts to conduct current, and the voltage across the PN will be the breakdown voltage. NOW, what limits this current is what happens to the transistor. No limit... POP.... just like a zener. But usually, there is a resistor in line, so the current is limited. You won't hurt the device unless you exceed the current of the junction. The same as a zener can last for years in the 'breakdown mode' if the current is set right.

If you read the transistor data sheet, there is also a spec for reverse breakdown of the base to emitter voltage. The same thing happens if you exceed this breakdown voltage. The transistor starts to conduct, and the emitter is held at this voltage above the base voltage. The first time I saw this it took me a couple of minutes to figure out just what was going on. Then it dawned on me that the reverse base to emitter voltage was being violated.

So, driving a transistor in this fashion could be considered 'biasing' it into the zener mode, but why oh why would you use a transistor instead of a zener, unless it needs more power through it than a zener can handle. But you don't generally drive power through a zener, it is just used to regulate a voltage and the power should come through the bias resistor and into the voltage circuit, with a minimal of current through the zener.
 
Mike odom

MIke:

That's a good point, Breakdown really is, and I forget which one (avalanche or Zener) and can be non-destructive if current limited. At 5.1 V both mechanisms are present. With a transistor the actual voltage of breakdown is not controlled. like it is in a Zener diode So, it could be 25 or 27 or even 30.
 
Correct KISS, they only give you the minimum MAX voltage that the process yields, so a transistor rated at 30V may not breakdown until 40V, but all transistors of that type will not breakdown under 30V.
 
I just talked to the company next door and they said:

They Do over voltage the transistors by 2 to 5 volts over the max. VCC

They call it a power curve ratio, more voltage on VCC you get less current on the output of the transistor

The power transistors don't get shorted or open from the over voltage on VCC, the transistors will DROP in output gain and power, that's when they know the transistor is damaged.

Bench checking them after they been damaged, it doesn't test shorted or open, because the breakdown voltage has been broken down

They do call it HIGH biasing or biasing the transistor to HIGH when you put the VCC more than max on the transistor
 
That is a lot of BS. The company next door to your company does not know anything about electronics.

If the Voltage on a transistor is higher than its maximum allowed voltage then its tiny collector-base junction might have avalanche breakdown which makes it very hot which destroys it. A zener diode has a HUGE junction that can dissipate the heat so it normally has avalanche breakdown.

Maybe the company makes a very brief pulse of over-voltage so that the tested transistor does not over-heat. But why don't they buy transistors that are allowed the higher voltage instead?
 
But why don't they buy transistors that are allowed the higher voltage instead?

I just asked them that and they said those power transistors cost more in dollars or cents compared to the transistor they get

Managers think of numbers remember

Plus they the managers told me they have a huge RMA return and repair income that keeps the company just making double per year

The repair techs told me out of 8 power transistors in the power amps , a least 3 transistor go bad , so they are still saving money

I still don't get this Power Curve they are talking about

The Techs, use a Meter that measures the Voltage to Current = Power output

Do you know what kind of meter this is?

It's for measuring Power transistors in power amps I guess to know how much Voltage to Current RATIO = Power output
 
In my electronics career I always cared for quality and reliability, not penny pinching.
I designed circuits with parts that would last a long time. I never over-voltaged or over-currented anything. I never allowed a part in my circuits to get hot.
The cost did not matter because none of my projects failed so no repairs were needed.

Some of my customers were the head offices of major banks and investment companies and the Canadian government.
 
Most of the Techs and Designers I meet are from ITT tech , they aren't that bright

I get most of my information from people like this and that's why I come here and ask you guys questions
 
The power transistors don't get shorted or open from the over voltage on VCC, the transistors will DROP in output gain and power, that's when they know the transistor is damaged.

Bench checking them after they been damaged, it doesn't test shorted or open, because the breakdown voltage has been broken down

er, no... they don't test open or shorted because they have only been damaged, not 'blown up'... and it's not because the breakdown voltage has been 'broken down'... you don't 'break down' the breakdown voltage. It may 'move' and not be as high because the chip is damaged.
 
The Techs, use a Meter that measures the Voltage to Current = Power output

Do you know what kind of meter this is?

It's for measuring Power transistors in power amps I guess to know how much Voltage to Current RATIO = Power output

Power = voltage X current... so, for the same power supplied, the higher the voltage, the lower the current, and vice versa.
 
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