2sc5200/2sa1493 With +/- 78vdc ?

[hienrich]

CONFUSED


I'M PLANNING TO ASSEMBLE AN AMP WITH 2SC5200/2SC1943
AND A PLUS/MINUS 78VDC AT THE RAILS. IS IT SAFE FOR THESE DEVICES WITH THAT SUPPLY RAILS?

AM I KILLING THEM? BUT IF POSSIBLE HOW MANY OF THESE DEVICES WILL I USE BETWEEN THE RAILS?


HIENRICH

[Duo]

You'll be absolutely fine with this power supply voltage of +-78VDC. These transistors can handle up to 230V, you're total power supply voltage is only 156 so there's no problem as far as too much voltage being on the transistors.

As far as how many to put in parallel for your speaker, lets see.

If you're doing 8 ohm load, then you'll probably get about 300W at that voltage. This means that at worst, the transistors dissipate about 200W(half swing). They'll have to also deal with 10A if you deliver a square wave at full clip into a resistive load. Turn this load into a speaker and that could become a lot more. Let's say about 18A to be safe. Being that these devices are good for 15A, it is simply a must to at least use two pairs in a channel.

Being that these devices are 150W each and 15A, I would say that four pairs are needed to be relatively safe.

On a 4 ohm load, you'll need a lot more.

[hienrich]

CONFUSED?

NOT ANY MORE. THANKS . THIS TIME IM GOING THRUOGH THE PLAN.



HIENRICH

[Duo]

Hehe, I'm glad I could help you out.

[Workhorse]

Originally posted by hienrich
CONFUSED


I'M PLANNING TO ASSEMBLE AN AMP WITH 2SC5200/2SC1943
AND A PLUS/MINUS 78VDC AT THE RAILS. IS IT SAFE FOR THESE DEVICES WITH THAT SUPPLY RAILS?

AM I KILLING THEM? BUT IF POSSIBLE HOW MANY OF THESE DEVICES WILL I USE BETWEEN THE RAILS?


HIENRICH

Hi Hienrich,

happy new year!

You can use 2SC1943/2SA5200 even at +-140VDC rails without any type of destruction.
QSC exculsively use these trannies at +-150VDC

Regards,
Kanwar

[uli]

Originally posted by Workhorse
You can use 2SC1943/2SA5200 even at +-140VDC rails without any type of destruction.

N E V E R ! ! !

They will blow in the first second of driving beyond their voltage capacity!

QSC exculsively use these trannies at +-150VDC

QSC uses them in class H configuration!
Class H (and Class G) is not comparable to Class B concerning supply rails.

Uli

[Duo]

haha, uli, I think he might mean 140V P-P, thus, +-70V rails.

+-140V would be 280P-P, and yes, that would destroy the transistor instantly as the swing approached 230.

Also, +-140 would yield about 1080Wrms into 8ohms. Might need just a few of these transistors in that situation even if they did that voltage. lol.

I do think, though, that people should be very specific whether they mean +-140 or +-70 being 140V rails.

I hope I clarified helpfully

EDIT: And if workhorse did mean actualy +-140V rails. hahaha.... ouch for those transistors.

[Eva]

QSC uses these transistors in such an arrangement that they are never exposed to more than 60V Vce when conducting [altough the 230V blocking capability is still required when not conducting]

For standard sagging +-78V rails use two pairs as an absolute minimum for 8 ohms loads and three pairs as an absolute minimum for 4 ohms loads

Feel free to add additional pairs, but be careful since there is a big fake market of 2SC5200/2SA1943 and the fake units have very poor dissipation capabilities [you would probably need 10 or more fake pairs for reliable operation at 4 ohms...]

[Duo]

yes eva knows the business.

Those absolute minimums are definitley minimums of course. Wouldn't want to accidentaly put 4ohms on an amp with just two pairs lol.

[AndrewT]

Hi,
No one has mentioned SOA curves for these devices YET.
5200/1943 are not particularly good above 60volts.
SOA shows absolute maximum DC current of 650mA @ 80volts.
This will apply to the transistor with the highest current draw in a parallel output. I would suggest that for short circuit condition you allow a maximum current per output transistor of between 50% and 70% of maximum say 400mA. 4 pairs will only carry 1.6amps. Again I suggest this is far too low for a 300w amp.
Next design consideration is maximum power. Current peak (Ipk) is about 78volts divided by 8 ohms giving 9.75 amps.
I recommend you design for Ipk at half supply volts to allow for inductive or capacitive loading into real 8 ohm speakers. This results in your ouput transistors carrying 9.75A @ 39v. 4 pairs give only a 25% margin at this voltage.
But the problem gets worse; you should consider designing the output stage and drivers for about half the intended load impedance which will double all the currents considered so far, and finally would you ever want to drive 4 ohm speakers or 2 *8ohms in parallel? then you have to quadruple all the currents.
We are not finished yet, you will be running quiescent current in the output stage? Then it follows that the transistors are at elevated temperatures. All the SOA data is based on a case temperature (Tc) of 25deg C. you now have to apply a reduction factor on all your design data at a fair guestimate of your running temp at the hottest time of the year and with maximum voltage coming from your electricity supplier.
I DO NOT recommend 1943/5200 at these rail volts!
Please do not suggest rails above 100volts without thinking (designing) of the consequences for the originator of this thread.
regards Andrew T.