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-   -   Complimentary power transistors in chip amp (http://www.diyaudio.com/forums/solid-state/40348-complimentary-power-transistors-chip-amp.html)

roshan101 2nd September 2004 08:28 AM

Complimentary power transistors in chip amp
 
2 Attachment(s)
Almost finished constructing an amp using the schematic published in an old Elektor mag. Only the transistors remain to be mounted. Problem is - these BD249/250 are outdated and aren't available anywhere. :( Should have checked this out before constructing. Anyway, thought I'll substitute these using TIP3055/2955, - since packaging is similar to BD249/250 - so its easy to mount in the existing PCB & heatsink, except current handling & power is a bit less ...I guess.


Being a novice at amp bulding.. Here's my question. Did I make the right choice? Do I need to change values of other components? Will my amp blow???

Amp is supposed to deliver 100W at 4 ohm load from a power supply of +- 18V, 5A.

roshan101 2nd September 2004 08:37 AM

datasheet
 
2 Attachment(s)
here's the datasheet for BD249

sayang001 2nd September 2004 09:07 AM

Futurlec has them, http://www.futurlec.com/TransPowerBD.shtml .

sajti 2nd September 2004 09:10 AM

Re: Complimentary power transistors in chip amp
 
Quote:

Originally posted by roshan101
Almost finished constructing an amp using the schematic published in an old Elektor mag. Only the transistors remain to be mounted. Problem is - these BD249/250 are outdated and aren't available anywhere. :( Should have checked this out before constructing. Anyway, thought I\'ll substitute these using TIP3055/2955, - since packaging is similar to BD249/250 - so its easy to mount in the existing PCB & heatsink, except current handling & power is a bit less ...I guess.


Being a novice at amp bulding.. Here\'s my question. Did I make the right choice? Do I need to change values of other components? Will my amp blow???

Amp is supposed to deliver 100W at 4 ohm load from a power supply of +- 18V, 5A.


The BD249/250 are the good old friends, but they are still in production. I can order them, and the cost is about 0.1USD...
I think the TIP2955/3055 is not strong enough for this application. I would use MJL21193/94...

sajti

cunningham 2nd September 2004 11:37 PM

You might also try TIP35 & TIP36.

Eva 3rd September 2004 01:04 AM

BD249C and TIP35C have nearly the same specifications, and also
BD250C and TIP36C are almost the same thing

BD249C and BD250C are still in production, at least from a company called Power Innovations

TIP35C and TIP36C are also in production from diverse companies like ST-Microelectronics, Mospec, KEC, On-Semi, etc... Try google for datasheets

These devices are pretty linear up to Ic=10A and with a single pair it\'s posible to drive a 4ohm load with +-40V rails without exceeding SOA. Their maximum ratings are Vce=100V, Ic=25A, Pd=125W

When using supply rails of +-40V or less these devices are a great and cheap alternative to the more expensive MJ15024/MJ15025, MJ21193/MJ21194, etc... They are also easier to mount due to its TO-218 case

roshan101 3rd September 2004 07:27 AM

Re: Re: Complimentary power transistors in chip amp
 
Quote:

Originally posted by sayang001
Futurlec has them, http://www.futurlec.com/TransPowerBD.shtml .
Quote:

Originally posted by sajti
The BD249/250 are the good old friends, but they are still in production. I can order them, and the cost is about 0.1USD...
I think the TIP2955/3055 is not strong enough for this application. I would use MJL21193/94...

Quote:

Originally posted by cunningham
You might also try TIP35 & TIP36.
Thanks, but I prefer to purchase locally. Dont want to go through import/customs hassles.
Have already wasted enough time & energy Searched for the BD\'s every nook & corner. I was aware TIP 35/36 were the nearest substitutes, but even these were\'nt available.

Quote:

Originally posted by Eva
These devices are pretty linear up to Ic=10A and with a single pair it\'s posible to drive a 4ohm load with +-40V rails without exceeding SOA. Their maximum ratings are Vce=100V, Ic=25A, Pd=125W

Considering the fact the chip here has a max voltage at +-22V, Increasing supply voltage beyond this is out of question. So dont you think even by using transistors with lower SOA, the efficiency should almost be same? I might be wrong here...dont know.

Have already soldered the TIP3055/2955. Switched the amp for a minute and it seems to be working. Except gain is a bit lower than expected & the TIP\'s are pretty cold. Will need to play the amp for a while to confirm this. Think I also need to check emitter collector voltage to make sure Transistor\'s are conducting. Will do the test later this evening.

Sajti - why do you say TIP3055/2955 cannot hold? They\'re supposed to be 90W, 60V, 15A.

Eva 3rd September 2004 08:43 AM

From the SOA point of view, TIP3055 and TIP2955 will work just fine [actually very happy] on that circuit since supply voltages are low and peak current is not likely to exceed 10A, however, be aware that :

- These transistors are slower than BD249/BD250 so check for signal-level dependent parasitistic oscillations and latching or other awful behaviors when clipping

- These transistors have a specified gain at Vce=4V of 100 for Ic=1A that drops to about 15 for NPN and 22 for PNP at Ic=10A, while BD249/BD250 show gains of 100 at Ic=1A that only drops to about 40 at Ic=10A. Lower gain means higher THD than expected, particularly at high frequencies

I don\'t understand why your local stores no longer sell the good old TIP35C/TIP36C/BD249C/BD250C but still sell more obsolete parts with inferior performance, like 2N3055, MJ2955 and \'3055\'/\'2955\' in diverse flavors :rolleyes::rolleyes::rolleyes:

roshan101 3rd September 2004 12:44 PM

High THD at high frequencies is not an issue. This amp is used to power a subwoofer. Hope I\'m not loosing too much in terms of power. Remember, this is a bridge amp and ther\'s a complimentary pair on either side of the output. So I assume the 100W might be achievable.
This leaves just the oscillations you\'ve mentioned that need to be checked.

I know its kind of frustating at times with the limited variety of components you get here. Any project you build has to be based on these standard set of components.

Eva 3rd September 2004 05:55 PM

To get 100W@4 ohms +-30V output swing is required, so I think the article refers to regulated supplies when it mentions +-18V, since the own circuit will probably drop the extra 3V on each rail before clipping

For a unregulated supply I would use the highest supply voltage supported by the IC to account for sagging


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