TDA 7250 based amplifier toasted!!!!

[zztop]

Has somebody build an audio amplifier based on IC TDA 7250 built by ST microelectronic?
I tryed but something is wrong!!!
When the heatsinks are cold it's all right, but at 40°C the darlington i used as finals starts oscillating and they toasted theyrself.

I think 40°C for an heatsink is right but ...... it doesn't work.

Somebody can help me

 

[trwh]

Hi

I may be able to help. I recently built a Velleman power amp kit based around the 7250. If you want, I can scan and post their schematic for you to try - its different from the designs given on the datasheet, and works very well (using TIP142/7 power darlingtons).

 

[Mr. Triatic]

?

hope you did´nt omit the 100nF capacitor between the supply +&- right next to the IC, i did that once, and made myself a toast just because of oscillations..
/L®

 

[Ford_V6]

I'am using a TDA7250 and TIP142/147. When i raise the volume the amp shuts down and when i lower the volume again the amp turns on. Why ?

 

[MaXiZ]

hope you did´nt omit the 100nF capacitor between the supply +&- right next to the IC

Where should be placed?

 

[djdan]

For Ford_V6

TDA7250 have a overload protection . When a overload will apear TDA7250 activate a mute circuit for 3 seconds. The reference is taken from power rezistor in series with supply.

 

[Andypairo]

Hi

I may be able to help. I recently built a Velleman power amp kit based around the 7250. If you want, I can scan and post their schematic for you to try - its different from the designs given on the datasheet, and works very well (using TIP142/7 power darlingtons).

I once built one with 2 modules bridged but it wasn't that stable...
can you post the schematic on the forums? It might be a good "backup" amp....

Cheers

Andrea

 

[IanHarvey]

For Ford_V6

TDA7250 have a overload protection . When a overload will apear TDA7250 activate a mute circuit for 3 seconds. The reference is taken from power rezistor in series with supply.

I found the overload protection was always set too low with the circuit values given. You can increase the trip current by reducing the resistor values, but this then has the disadvantage that this puts up the bias current by the same factor, and the amp runs hot. In the end, what I did was put (IIRC) a 270K resistor between pins 7 and 17 of the chip (the two current sense inputs), which fooled it into turning the bias current back down.

I also found the TDA7250 was a bit prone to blowing up, probably due to overheating, if it was socketed. I've now got it soldered straight in with a DIL heatsink on top, and it's been fine since.

Cheers
IH

 

[mcp]

TDA 7250 Schematic

Originally posted by Andypairo
I once built one with 2 modules bridged but it wasn't that stable...

Hi Andrea

A working schematic on the TDA7250 can be found here.
Tda7250 schematic -- "Click" on "schematic" to open window.

You can easily bridge the 2-channels for 150W/8 ohms output.

 

[Ford_V6]

Can i drive this amp safely with a 650 W 2*32 V toroidal ??

 

[mcp]

Yes you can, but you will be working at almost maximum voltage of +-45V. The TDA7250 chip will get slightly hot, so best to put some heatsink on it.

I run mine at 2*27 - which works out to +-35V. This is the recommended working voltage. No heatsinks necessary for chip.

With a 650W transformer, you can run 3x TDA7250. Just nice for a 6 channel HT amp.

 

[Ford_V6]

Thnaks for the hint.

 

[radio]

Hello all !
Is anyone able to offer the reliable schematic and the PCB for this audio amplifier with TDA7250 with output drivers 2N30055/MJ2955 !?
Since has 10 pieces 2N3055 and 10 pieces MJ2955!
thanks