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 Problem is - these BD249/250 are outdated and aren't available anywhere.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.
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.
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roshan101 said: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 Problem is - these BD249/250 are outdated and aren't available anywhere.
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
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
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
Re: Re: Complimentary power transistors in chip amp
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.
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.
sayang001 said:
sajti said:
cunningham said:
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.
Eva said:
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.
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
- 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
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.
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.
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
For a unregulated supply I would use the highest supply voltage supported by the IC to account for sagging
The Radio Amateus power supplies can be good to you
Normally they used 17 plus 17 volts AC, heavy rectifiers and heavy output transistors, most of those supplies are designed to hold continuosly 200 watts, supplying 13.8 volts.
Internal DC Voltage is around 24 Volts DC that goes to stabilizer and series regulation 2n3055 units.... each one holding 30 watts of heat normally.
I think one of that can be good to you, as i can see you normally use low voltage in your amplifiers...you can adjust internally to 18 Volts.... it will give you the same 200 watts....11 amperes easy in this case.... and the transistors will be cold...because the 24 volts will drop a lot...you will have 2 or 3 volts over transistors.
Almost all those supplies uses series regulation, with one error transistor in the output, with a trimpot in the center of output voltage divider and some darlington connections to the parallelled 2N3055.
I think this can be very usefull to you...your dream supply!
regards,
Carlos
Normally they used 17 plus 17 volts AC, heavy rectifiers and heavy output transistors, most of those supplies are designed to hold continuosly 200 watts, supplying 13.8 volts.
Internal DC Voltage is around 24 Volts DC that goes to stabilizer and series regulation 2n3055 units.... each one holding 30 watts of heat normally.
I think one of that can be good to you, as i can see you normally use low voltage in your amplifiers...you can adjust internally to 18 Volts.... it will give you the same 200 watts....11 amperes easy in this case.... and the transistors will be cold...because the 24 volts will drop a lot...you will have 2 or 3 volts over transistors.
Almost all those supplies uses series regulation, with one error transistor in the output, with a trimpot in the center of output voltage divider and some darlington connections to the parallelled 2N3055.
I think this can be very usefull to you...your dream supply!
regards,
Carlos
Eva said:
Eva,
Going by your advise, I've decided to invest in a 18-0-18V, 5A Transformer. No-load voltage should work to about +-24V, i.e. 2V greater than ic's absolute maximum of +-22V. Hope this is OK. The next lower voltage transformer available is only 12-0-12, 5A.
The same schematic was published in another article in elektor, but this time with a power supply of 12-0-12, 7A transformer. No special regulation but 22,000 MFD *2 caps. This could be a typo - not sure. The author claims it can deliver 200W .
The original schematic was designed for public address systems which can operate on 12V car batteries.
Carlos, Is that your son?
Radio amateur supply ....sounds expensive, but would certainly be my dream supply.
Rosham, thank you the attention, the little girl
Is my last daughter (hehe, maybe...not sure!), i have four beautifull girls, and my Spanish beauty, my wife.
As Arabic people, i have my own "harém", and i am proud of that.
Only girls here.... also a Maid...this is wonderfull!
Larissa Rapela is her name...now with Spain Passport, will to go Orenz Barbadannes, where the family started.
by
Carlos
Is my last daughter (hehe, maybe...not sure!), i have four beautifull girls, and my Spanish beauty, my wife.
As Arabic people, i have my own "harém", and i am proud of that.
Only girls here.... also a Maid...this is wonderfull!
Larissa Rapela is her name...now with Spain Passport, will to go Orenz Barbadannes, where the family started.
by
Carlos
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It seems to me that a very important point has been missed. The opamps in the schematic given in post#1 are TDA2030 chip amps from Philips, and the schematic shows a method of extracting more power out of them. The reason +/-18v is used is that this is the maximum supply voltage for these chips. An 18v-0-18v transformer will blow them up.
18-0-18V transformers tend to produce +-27V after rectification with no load since those 18V are rated at full load instead of no load
+-22V at idle may be OK for this IC but +-27V may be too high for most units, altough some units may survive. In case of blown ICs an easy solution is to add turns to the transformer in order to reduce those 18-0-18V to 14-0-14V or add some kind of regulation
+-22V at idle may be OK for this IC but +-27V may be too high for most units, altough some units may survive. In case of blown ICs an easy solution is to add turns to the transformer in order to reduce those 18-0-18V to 14-0-14V or add some kind of regulation
18v-0-18v is the absolute maximum for the TDA2030 chip.
The LM1875 is pin - compatible with the TDA2030, the same PCB can be used for both, and it will work fine with the 18v - 0 - 18v transformer. It has better performance too. The circuit may need some changes, because the quiescent current will be different, but it's capable of more power.
The LM1875 is pin - compatible with the TDA2030, the same PCB can be used for both, and it will work fine with the 18v - 0 - 18v transformer. It has better performance too. The circuit may need some changes, because the quiescent current will be different, but it's capable of more power.
Actually I'm using TDA 2030A . This has a max supply is +-22 , as compared to +-18 of TDA 2030. Anyway I've decided to get down to 12-0-12V transformer. While testing, found the chip tends to get too hot under excess voltage. You guys are right. The chip wont hold.
Carlos...4 kids and a beautiful wife....a very happy family indeed!!
Carlos...4 kids and a beautiful wife....a very happy family indeed!!
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