Hi:
I am repairing a 250W ligth power supply, medical equipment, it turns on a DC bulb, from 0 volts to 24, 250watts. it uses a switching power supply, controls from 0 to 24 volts, varing the ligth intensity. The two input switching transistor are damaged and don´t have their codes. I replaced with ecg 379 (swtich, 12 amperes, 900 volts), the power supply turned on and worked (0 to 24volts), but when i put the 250 watts bulb , only worked a few minutes because the two switching transistor are damaged again. I need another code transistor to reach a good job.
Please someone knows about.
thanks
Néstor

 

Not much help, but:

1) 250W / 24V = 10.4A, this means you probably need about a 20A part for heat dissipation. Your 12A part probably died from heat exhaustion.

2) What type of xstr, bipolar or FET? Most switching power supplies use NMOS FETs with low on resistance, but this doesn't eliminate the use of bipolar.

3) Is it also possible these are not xstr's, but SCR or triacs (can be same pkg as xstr)?

4) Try to find a schematic somewhere. If you do, post it.

 

NTE/ECG 389 datasheet

Do you recall the original part number of the part you replaced?