Over Voltage rating on transistors, is this called biasing?

[Billy Mayo]

Most bipolar transistors have a max rating at 24 volts and power transistors max rating are generally ?

The company next door to my work , over voltage the transistors and power transistors

They call it biasing the transistors , but its over the max rating that the transistors can take, so they get very hot and stresses them out so they don't last more than 6months to a year

I thought biasing was getting the transistor to the right Q point to the positive and negative cycles don't clip or distort

What this company does to transistor is they put a over voltage on the transistor on the +VCC

What is this called what they are doing to the transistor?

 

[KeepItSimpleStupid]

abusing the transistor. To the company only one thing matters. Lasting just beyond the warranty.

Transistors should be operated within their SOA or Safe Operating Area.

 

[crutschow]

Biasing is setting the operating point to the desired value for proper operation of the transistor. It has nothing whatsoever to do with operating the transistor outside its limits which an absolute no-no if you want reasonably reliable operation of the device.

 

[Billy Mayo]

Biasing is setting the operating point to the desired value for proper operation of the transistor. It has nothing whatsoever to do with operating the transistor outside its limits which an absolute no-no if you want reasonably reliable operation of the device.

True I agree

But what it is called when you raise the VCC past the max limit?

The VCC voltage Min and max DC voltage is Biasing the transistor right?

It says on the Datasheets what the Max. and min VCC you can supply on a transistor, is this biasing? or what is the DC VCC voltage doing to the transistor? it's setting up a biasing limit? for the positive and negative cycles to swing from the max VCC voltage

 

[audioguru]

The datasheet for a transistor does not say a minimum VCC. VCC is the supply voltage for the transistor circuit.
If an NPN transistor does not have a load, does not have an emitter resistor but has a collector resistor then its collector can swing up to VCC and almost down to ground. Usually A transistor AC amplifier is biased so that its collector voltage is at half of VCC when there is no input signal.

 

[Nigel Goodwin]

The VCC voltage Min and max DC voltage is Biasing the transistor right?

No, wrong - it's nothing to do with biasing.

 

[Billy Mayo]

what is the VCC voltage doing to the transistor than if it isn't biasing it?

if the VCC is more than 24 volts on a bipolar transister 2904 it will fry it and make it get hot

 

[Nigel Goodwin]

what is the VCC voltage doing to the transistor than if it isn't biasing it?

It's destroying it if it's too high.

Biasing is arranging the desired current through the transistor, so as it operates on the required part of the curve.

Generally (but not always, depending on what you require) you bias a transistor so as to allow the maximum output range.

 

[large_ghostman]

why would a company do this on purpose? it dosnt make sense???? surely the cost is not relevant if your product does not work correctly or you get a name of poor quality products! surely that would cost a company more than a slightly more capable transistor?? or am i missing something??

 

[Nigel Goodwin]

why would a company do this on purpose? it dosnt make sense???? surely the cost is not relevant if your product does not work correctly or you get a name of poor quality products! surely that would cost a company more than a slightly more capable transistor?? or am i missing something??

Well we've only got one persons suggestion that they are doing that, and much of what he claims doesn't make sense.

If you deliberately design a circuit to exceed the transistors max ratings it WILL fail, and not 'just out of warranty', the vast majority will fail the first time they are turned on - although you 'may' be lucky and get one or two per hundred that happen to exceed their ratings, and will be fine.

I don't believe what he claims, and there are a number of possible 'reasons':

1) He didn't understand what he was told.

2) The person who supposedly told him didn't understand it.

3) He was been wound up.

4) We are been wound up.

 

[audioguru]

what is the VCC voltage doing to the transistor than if it isn't biasing it?

if the VCC is more than 24 volts on a bipolar transister 2904 it will fry it and make it get hot

 

[audioguru]

Just a Moderation text test, for 'agu'.

Eric

 

[large_ghostman]

that makes alot more sense mr nigel

 

[MrAl]

Most bipolar transistors have a max rating at 24 volts and power transistors max rating are generally ?

The company next door to my work , over voltage the transistors and power transistors

They call it biasing the transistors , but its over the max rating that the transistors can take, so they get very hot and stresses them out so they don't last more than 6months to a year

I thought biasing was getting the transistor to the right Q point to the positive and negative cycles don't clip or distort

What this company does to transistor is they put a over voltage on the transistor on the +VCC

What is this called what they are doing to the transistor?

Hello,

Your best bet is to ask THEM. They are the only ones that can tell you this information. They might be stress testing the transistors which is usually done to quickly obtain data that can be extrapolated to predict the long term longevity of the transistor under normal operating conditions.

The word "bias" really just means to apply a DC voltage in most circuits. You can in fact bias it too high and blow it out, but it all depends on what your reason for biasing it is in the first place.

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 and then maybe study the amplification, distortion, etc., of the circuit.
If you bias it for a stress test, then you may apply higher than usual DC voltages and higher than usual temperatures and then study the failure rate, and the failure rate may help you to set the max voltage specification for that particular transistor.

 

[large_ghostman]

Hello,

then you may apply higher than usual DC voltages and higher than usual temperatures and then study the failure rate, .

ah so thats what ive been doing is called so i didnt brick or toast them i stressed tested them! man i have stress tested a fair few

 

[MrAl]

ah so thats what ive been doing is called so i didnt brick or toast them i stressed tested them! man i have stress tested a fair few

Ha ha ha, yeah i think we all have done our fair share of "stress testing" transistors and other devices in the past

 

[Billy Mayo]

what does biasing to high mean? more than half of the supply voltage on the base?

 

[MrAl]

Hi,

You are asking such general questions that im not sure if you will be happy with the answers. Might as well ask what color we can paint a transistor

You can bias the transistor to any voltage or current you like, but some levels will be more useful than others depending on what you are using the transistor for. For example if you are using it for an amplifier then you might want to bias it around 1/2 Vcc or something like that. Then in this context biasing it too high would mean that you've biased it so much that the output is almost in saturation already. That's not destructive but it doesnt make the amp work very well either.
Then for some apps there is emitter base reverse bias, which if you go too high on that the base emitter diode blows out, and this can happen with as little as 10 volts for many different part number transistors.
This would often happen when a tech puts the transistor in the socket or board with emitter and collector accidentally reversed. The collector is often biased to some higher voltage like 9v to 15v, and with the emitter where the collector is that puts almost the whole voltage reversed across the emitter base, blowing out the transistor (even though the current could be only microamps). Then when the transistor is reversed in an attempt to fix it, we find the gain has gone down to a much much lower level even though the transistor sometimes still seems to work a little, but it does not work in the original application anymore or else it blows out completely.

 

[rumpfy]

Sorry billy, but the premise of the question is quite incorrect.
"Most bipolar transistors have a max rating at 24 volts and power transistors max rating are generally ?"
This is just not accurate.
For operation in what is called the 'linear' range', biasing is quite important from the signal distortion point of view; However when used as a switch, the ratings depend very much on the bias AND the drive conditions. It is quite typical for a transistor to have a Vce rating of say 24 volt with an open circuit base, but with a Vbe resistance of say 1000 ohm, the Vce rating(Vcer) is increased to say 50 volt.
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 but with different base emitter drive configurations.

 

[Billy Mayo]

biasing it too high would mean that you've biased it so much that the output is almost in saturation already.

I still don't get what is biasing too high mean

Because when I would Bias power amps solid state or tubes power amps, I would use a Clean sine waveform at 1K hz and adjust the biasing trim pot so the power amps push pull was not clipping or had any DC component , transistor OFF time cross over

So Biasing too high means you would clip the positive and negative cycles?