2SC1775A/2SA872A equiv but with higher VCE max

[Massilia]

Hi,

I would like to find some equivalents of the famous 2SC1775A/2SA872A bipolar devices, but with higher VCE max (ideally 150V max, against 120V max).

Do you know if it exists, and their references?

Many thanks in advance

Regards

Bruno

 

[AndrewT]

the only parameters that are less common are hFE being higher and Noise being specified by graphs.

There are probably more than a few alternatives that can match, or better, the a872 and >=150Vce0

Have you looked at Greg's comparison charts/tables?

 

[Massilia]

Thank you Andrew for your response.
Whre can I find this Greg's comparison charts/tables?

Thanks!

 

[AndrewT]

typed greg transistor table and the first result is:
Small Signal Transistors

But, not helpful.
The only two are 42/92 and 5551/5401 and these can never be considered equivalents.

 

[Massilia]

Indeed... 😀

So if someone knows a good replacement of 2SC1775A/2SA872A whith VCE>=150V I am very interested!

Thanks

 

[sgrossklass]

These transistors' combination of hFE, Vceo and Cob is bordering on a miracle to begin with. Use a cascode.

 

[Massilia]

Since I do not use the transistors in the first stage of the amplifier (a cascoded differential based on SSM2210 excellent matched transistor); but in in the second stage of the amplifier, before darlington complementary push-pull follower, I need to have the whole amplitude on the 2nd stage output needed for a 250WRms/8 Ohms amp.

So I can't use a cascode for the 2nd stage of my amp (where the 2SC1775A/2SA872A are used). The VCEmax of those transistors at full power are closed to 125V... a bit too risky!

Thanks

 

[AndrewT]

Use a VAS type transistor.
Greg has a table for those as well.

250W into 8ro from 125Vdc rail to rail voltage !!!!!

You can cascode the VAS. Many choose to do this.

 

[Massilia]

250W into 8ro from 125Vdc rail to rail voltage !!!!!

No... 126.5V output swing pk-pk for 250WRms/8 Ohms
The power rails are obviously higher.
Since I do not use a common source for the output stage, I have no gain for that; so +/-63V pk must be delivred from the 2nd stage of the amplifier.

 

[Ian Finch]

It seems those unobtanium Hitachi transistors are often sought here (unsuccessfully) but the only parts available are as usual, poor copies from China with low gain.
Any BJT still manufactured, having Vceo > 150V, is going to have limited Hfe and dissipate a fair amount of heat at that voltage - too much for a TO92, I would think. As already posted, if you want higher Vceo and high Hfe, better to use cascoded HV transistors. If necessary, use boosted rails for the required extra voltage swing. If you don't really require a lot of a gain, why not video drivers like KSC3503/A1381?

However, these low current, low Cob driver clones from Profusion may have enough gain to suit:
2SD669A-B-TM3-T PDF Datasheet - Unisonic Technologies Co., Ltd. - Datasheets360.com
http://www.utc-ic.com/uploadfile/2011/1101/20111101111250426.pdf

 

[AndrewT]

250W into 8ro from 125Vdc rail to rail voltage !!!!!

No... 126.5V output swing pk-pk for 250WRms/8 Ohms
The power rails are obviously higher.
Since I do not use a common source for the output stage, I have no gain for that; so +/-63V pk must be delivred from the 2nd stage of the amplifier.

the voltage rating for the VAS and all the output transistors is at least the rail to rail voltage.
But that is the minimum voltage rating. These transistors MUST also meet the SOA requirements for the duty.
This usually results in the voltage rating much exceeding the rail to rail voltage. I have seen 350Vce0 devices used, in a +-60Vdc supply, to get sufficient SOA.

I thought you were quoting the rail to rail voltage when you said 125Vdc.
You are obviously unaware of the design considerations required for this amplifier.

That revelation now prompts the questions:
Why are you replacing the transistors?
Is it because they have blown?
Why did they blow?

 

[sgrossklass]

the voltage rating for the VAS and all the output transistors is at least the rail to rail voltage.
But that is the minimum voltage rating. These transistors MUST also meet the SOA requirements for the duty.
This usually results in the voltage rating much exceeding the rail to rail voltage. I have seen 350Vce0 devices used, in a +-60Vdc supply, to get sufficient SOA.

Like, for example, BF470/471. These may only be rated at 30 mA but they have one handy feature - a TO-126 case. Makes it much easier to keep them cool when compared to TO-92, and that in turn means secondary breakdown is pushed to higher currents. If you need a VAS current of 10 mA with +/-60V rails, that means a Pdiss of close to 600 mW - forget about using a TO-92 there.