Reply by amal banerjee●December 14, 20222022-12-14
On Tuesday, December 13, 2022 at 8:11:44 PM UTC+5:30, Fred Bloggs wrote:
> On Tuesday, December 13, 2022 at 1:19:41 AM UTC-5, daku...@gmail.com wrote:
> > On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
> > > On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
> > > > A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
> > > > In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
> > > > In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
> > > > Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
> > > > amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
> > > > Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
> > > If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
> > I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
> > 1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
> > 2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
> > _
> A functioning transistor will not behave as you describe. There must be something wrong with your test setup. Is the transistor plugged in wrong, or is there an issue with ICE to voltage conversion for the display, or some other problem?
> Rule number one for engineers: If your test setup leads to the discovery of an entirely new property for the device under test -> something is wrong with the setup.
I am using a Keithley 6842 picoammeter and a Keithley 2230G triple output DC and programmable power supply. The same transistor is used for continous DC Vbe|Vce and pulsed DC Vbe|Vce. So if the continous DC Vbe|Vce method generates the correct family of curves, why would it fail in the pulsed DC Vbe|Vce case ? There are collector and base resistors as well.
Reply by Fred Bloggs●December 13, 20222022-12-13
On Tuesday, December 13, 2022 at 11:52:36 AM UTC-5, John Larkin wrote:
> On Tue, 13 Dec 2022 16:37:24 +0100, Jeroen Belleman
> <jer...@nospam.please> wrote:
>
> >On 2022-12-13 16:19, John Larkin wrote:
> >> On Mon, 12 Dec 2022 22:19:37 -0800 (PST), amal banerjee
> >> <daku...@gmail.com> wrote:
> >>
> >>> On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
> >>>> On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
> >>>>> A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
> >>>>> In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
> >>>>> In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
> >>>>> Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
> >>>>> amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
> >>>>> Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
> >>>> If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
> >>>
> >>> I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
> >>> 1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
> >>> 2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
> >>> _
> >>
> >> Thermal time constants are complex, but a first guess of 100
> >> milliseconds first-order is a reasonable place to start.
> >>
> >> Pulse for a few hundred milliseconds at some fixed Vc and observe the
> >> Ic waveform during the pulse. Wait a minute before pulsing again.
> >>
> >> Everything electrical, namely non-thermal, will be settled in
> >> nanoseconds in an SiGe transistor.
> >>
> >
> >It sounds to me like his pulsed sources aren't doing what he thinks
> >they should be doing.
> >
> >Alternatively, his pulse sources may have enough parasitic reactances
> >to make the transistor scream at some high frequency.
> >
> >Jeroen Belleman
> Good point about oscillation. Fast transistors are tricky in wideband
> circuits.
Not if it's properly terminated and the power supply is choked. Maybe he did choke the power supply with some crummy hi-Q thing. Seems it would be just as likely to oscillate in DC as well as pulsed mode.
>
> He could touch various nodes with a pencil or a small screwdriver and
> see if anything changes.
>
> Base resistors sometimes help.
Reply by John Larkin●December 13, 20222022-12-13
On Tue, 13 Dec 2022 16:37:24 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
>On 2022-12-13 16:19, John Larkin wrote:
>> On Mon, 12 Dec 2022 22:19:37 -0800 (PST), amal banerjee
>> <dakupoto@gmail.com> wrote:
>>
>>> On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
>>>> On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
>>>>> A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
>>>>> In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
>>>>> In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
>>>>> Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
>>>>> amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
>>>>> Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
>>>> If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
>>>
>>> I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
>>> 1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
>>> 2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
>>> _
>>
>> Thermal time constants are complex, but a first guess of 100
>> milliseconds first-order is a reasonable place to start.
>>
>> Pulse for a few hundred milliseconds at some fixed Vc and observe the
>> Ic waveform during the pulse. Wait a minute before pulsing again.
>>
>> Everything electrical, namely non-thermal, will be settled in
>> nanoseconds in an SiGe transistor.
>>
>
>It sounds to me like his pulsed sources aren't doing what he thinks
>they should be doing.
>
>Alternatively, his pulse sources may have enough parasitic reactances
>to make the transistor scream at some high frequency.
>
>Jeroen Belleman
Good point about oscillation. Fast transistors are tricky in wideband
circuits.
He could touch various nodes with a pencil or a small screwdriver and
see if anything changes.
Base resistors sometimes help.
Reply by Jeroen Belleman●December 13, 20222022-12-13
On 2022-12-13 16:19, John Larkin wrote:
> On Mon, 12 Dec 2022 22:19:37 -0800 (PST), amal banerjee
> <dakupoto@gmail.com> wrote:
>
>> On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
>>> On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
>>>> A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
>>>> In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
>>>> In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
>>>> Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
>>>> amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
>>>> Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
>>> If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
>>
>> I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
>> 1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
>> 2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
>> _
>
> Thermal time constants are complex, but a first guess of 100
> milliseconds first-order is a reasonable place to start.
>
> Pulse for a few hundred milliseconds at some fixed Vc and observe the
> Ic waveform during the pulse. Wait a minute before pulsing again.
>
> Everything electrical, namely non-thermal, will be settled in
> nanoseconds in an SiGe transistor.
>
It sounds to me like his pulsed sources aren't doing what he thinks
they should be doing.
Alternatively, his pulse sources may have enough parasitic reactances
to make the transistor scream at some high frequency.
Jeroen Belleman
Reply by John Larkin●December 13, 20222022-12-13
On Mon, 12 Dec 2022 22:19:37 -0800 (PST), amal banerjee
<dakupoto@gmail.com> wrote:
>On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
>> On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
>> > A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
>> > In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
>> > In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
>> > Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
>> > amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
>> > Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
>> If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
>
>I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
>1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
>2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
>_
Thermal time constants are complex, but a first guess of 100
milliseconds first-order is a reasonable place to start.
Pulse for a few hundred milliseconds at some fixed Vc and observe the
Ic waveform during the pulse. Wait a minute before pulsing again.
Everything electrical, namely non-thermal, will be settled in
nanoseconds in an SiGe transistor.
Reply by Fred Bloggs●December 13, 20222022-12-13
On Tuesday, December 13, 2022 at 1:19:41 AM UTC-5, daku...@gmail.com wrote:
> On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
> > On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
> > > A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
> > > In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
> > > In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
> > > Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
> > > amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
> > > Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
> > If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
> I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
> 1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
> 2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
> _
A functioning transistor will not behave as you describe. There must be something wrong with your test setup. Is the transistor plugged in wrong, or is there an issue with ICE to voltage conversion for the display, or some other problem?
Rule number one for engineers: If your test setup leads to the discovery of an entirely new property for the device under test -> something is wrong with the setup.
Reply by amal banerjee●December 13, 20222022-12-13
On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote:
> On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
> > A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
> > In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
> > In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
> > Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
> > amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
> > Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
> If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms.
1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case.
2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained.
_
Reply by Fred Bloggs●December 12, 20222022-12-12
On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote:
> A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
> In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
> In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
> Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
> amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
> Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind.
Reply by John Larkin●December 12, 20222022-12-12
On Mon, 12 Dec 2022 00:01:59 -0800 (PST), amal banerjee
<dakupoto@gmail.com> wrote:
>A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
>In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
>In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
>Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
>amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
>Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
>
>
The differences between DC and pulsed curves are usually thermal. That
transistor is so fast that your pulses (milliseconds or microseconds?)
are effectively DC electrically.
If you make long pulses, into the 10s or 100s of milliseconds, you can
see the thermal effects on the curves. Until it blows up.
There are tricks to actually measure junction temperature while
pulsing. Mosfets use the substrate diode and bipolars can use the b-e
junction as the temperature sensor.
As Phil H has noted, the Early voltage of SiGe parts is huge. In other
words, the Ic vs Vc curve is very flat absent thermals.
If you see a drooping Ic/Vc (or Id/Vd) curve, a reverse Early voltage,
that's usually thermal.
Reply by Anthony William Sloman●December 12, 20222022-12-12
On Monday, December 12, 2022 at 7:02:04 PM UTC+11, daku...@gmail.com wrote:
> A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor.
> In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet.
> In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are.
> Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce
> amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the
> Vce pulses are. Thanks in adbvance for your hints|help|suggestions.
https://www.infineon.com/dgdl/Infineon-BFQ790-DS-v02_00-EN.pdf?fileId=5546d4624cb7f111014d237c2a8f54fc
Table .2 on page 6 lists the collector base capacitance as typically 1.1pF at Vce at 5V. It's a varactor
and Figure 7 on page 11 shows how it varies with Vce.
Most of the charge is injected into the base when Vce starts rising, and progressively less - in Coulombs per volt - as Vce goes up.
A good Spice model for the transistor might capture that.
--
Bill Sloman, Sydney