input stage transistor

pdp11 · 2nd May 2010, 03:41 PM

Hi all
I'm now designing a class AB mosfet amplifier with IRF240 and IRFP9240.
Since now I have not designed any mosfet amplifier and any amplifier with high voltage supply.
The supply voltage are probably +-45/50V
I'm thinking to use mmbt5401/mmbt5551 (th: 2n5401/2n5501) or fjv992/fjv1845 (th: ksa992, ksc1845) for the current mirror input stage if I'll wish more hfe.
For the VAS i'm thinking to use ksa1201/ksc2881.
What do you think about those transistors? I haven't seen those in many design.
Are a good choice?
Any other idea regarding SMD transistor for driving a 100V mosfet design?

PS: sorry for my bad english.

nigelwright7557 · 2nd May 2010, 06:37 PM

I use MPSA42 for LTP and its constant current source.

For the VAS and its current source I use MJE340 and MJE350.

AndrewT · 06:46 PM

I don't know what voltages the smd types are available in, but for a +-50Vdc amp you may have to consider cascoding to get these tiny devices within their thermal and voltage limits.

For both LTP and VAS you need good hFE over the range of working currents, low Cob at 5V and 10Vce, medium to high fT at your working currents.

pdp11 · 3rd May 2010, 05:04 PM

thanks for answares.
Both couple mpsa42/92 and mje340/350 have smd brothers.
I prefer avodi cascode input stage for many reason, the first is that increase complexity without a sound improvement.
SMD transistors placed correctly offer a better termal uniformity and less noise than a trough hole solution.
I will calculate the heating of all transistor during the components choice.

Telstar · 15th January 2011, 08:16 PM

Hey pdp, what did you go for in the end?

moschfet · 15th January 2011, 08:37 PM

hi pdp11,

my english is also bad, so I hope we can communicate

Do you know == Diodes, Inc. == ? Since there are a lot of interesting transistor.

tommy1000 · 16th January 2011, 08:22 PM

Quote:

Originally Posted by moschfet

hi pdp11,

my english is also bad, so I hope we can communicate

Do you know == Diodes, Inc. == ? Since there are a lot of interesting transistor.

What transistors from diodes.com do you reccomend?

moschfet · 16th January 2011, 10:10 PM

I like SMDs, but I don't like to work with it. So I build my amps with big devices. In one of my next projects I will evaluate an amp with SMDs.

MMDT5401 and MMDT5551 are very interesting, because there are two transistors in one case. Important for mirrors and diffamps. I have very good experience with 2N5551/5401, so I give them a try.

CBS240 · 17th January 2011, 05:14 AM

Most of those SMDs come in duel or quad packages which makes for many less 'components' to solder.

tommy1000 · 17th January 2011, 05:48 PM

Thank you.

2nd May 2010, 03:41 PM	#1
pdp11 diyAudio Member Join Date: Apr 2010	input stage transistor Hi all I'm now designing a class AB mosfet amplifier with IRF240 and IRFP9240. Since now I have not designed any mosfet amplifier and any amplifier with high voltage supply. The supply voltage are probably +-45/50V I'm thinking to use mmbt5401/mmbt5551 (th: 2n5401/2n5501) or fjv992/fjv1845 (th: ksa992, ksc1845) for the current mirror input stage if I'll wish more hfe. For the VAS i'm thinking to use ksa1201/ksc2881. What do you think about those transistors? I haven't seen those in many design. Are a good choice? Any other idea regarding SMD transistor for driving a 100V mosfet design? PS: sorry for my bad english.

2nd May 2010, 06:37 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	I use MPSA42 for LTP and its constant current source. For the VAS and its current source I use MJE340 and MJE350. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

2nd May 2010, 06:44 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I don't know what voltages the smd types are available in, but for a +-50Vdc amp you may have to consider cascoding to get these tiny devices within their thermal and voltage limits. For both LTP and VAS you need good hFE over the range of working currents, low Cob at 5V and 10Vce, medium to high fT at your working currents. __________________ regards Andrew T. Last edited by AndrewT; 2nd May 2010 at 06:46 PM.

15th January 2011, 08:16 PM	#5
Telstar diyAudio Member Join Date: Dec 2007	Hey pdp, what did you go for in the end? __________________ The response of the inner ear extends to at least 200khz - Dr W. Tempest

17th January 2011, 05:14 AM	#9
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Most of those SMDs come in duel or quad packages which makes for many less 'components' to solder. __________________ All the trouble I've ever been in started out as fun......


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3rd May 2010, 05:04 PM	#4
pdp11 diyAudio Member Join Date: Apr 2010	thanks for answares. Both couple mpsa42/92 and mje340/350 have smd brothers. I prefer avodi cascode input stage for many reason, the first is that increase complexity without a sound improvement. SMD transistors placed correctly offer a better termal uniformity and less noise than a trough hole solution. I will calculate the heating of all transistor during the components choice.

15th January 2011, 08:37 PM	#6
moschfet diyAudio Member Join Date: Jul 2008 Location: Hannover	hi pdp11, my english is also bad, so I hope we can communicate Do you know == Diodes, Inc. == ? Since there are a lot of interesting transistor.

16th January 2011, 10:10 PM	#8
moschfet diyAudio Member Join Date: Jul 2008 Location: Hannover	I like SMDs, but I don't like to work with it. So I build my amps with big devices. In one of my next projects I will evaluate an amp with SMDs. MMDT5401 and MMDT5551 are very interesting, because there are two transistors in one case. Important for mirrors and diffamps. I have very good experience with 2N5551/5401, so I give them a try.

17th January 2011, 05:48 PM	#10
tommy1000 diyAudio Member Join Date: Mar 2008	Thank you.

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