Tool/software:
When I apply -10 to -30vdc to the lower XSTR collector, the output dies and the op-amp heats up. when I disconnect the Base of that -V XSTR the pulse comes back and the op-amp goes back to room temp. as of now I can't use the output XSTRs to buffer my output. This XSTR configuration can allow up to 1 amp current sourcing.
circuit being used below:
Hi John,
The quiescent current in OPA454 is approx. 4mA. If Vcc = 50Vdc and Vee = -30Vdc, the quiescent power will be approx. 80V*4mA = 0.32W. If Vee = -10V, the quiescent power dissipation is 60V*4mA = 0.24W.
If the OPA454 is properly heatsink to the PCB surface (say with 2oz area, well dissipated to the PCB copper layers)
If the OPA454 is sourcing or sinking higher current, then the dissipated power per a load will increase the Tj. In order to limit the OPA454's power dissipation, you can lower the supply voltage rails according to your output swing. The (Vcc - Vout)*Iout+ is the power dissipation on the positive driver side, and abs(Vee - Vout)*Iout- attributes to the power dissipation on the negative driver side. So some of the power dissipation on both Vcc and Vee are increased and more heat is being generated in OPA454. This is likely what is occurring.
In addition, R3 is the resistor is delivering current when both NPN and PNP are operating in inactive region, when Vbe <approx. abs (0.7Vdc + Iout*0.2Ω). Anyway, you can increase R3 from 20Ω to 100Ω-200Ω range (depending on your load current). By increasing R3 value, it will lower the OPA454's source/sink current and keep it cooler.
If the RL is operating in continuous waveform, the R3 value may affect the distortion across the BJTs' non-conductive region. If the output voltage is operating in square wave of discrete output setpoint, R3 value may be configured in higher value or remove it completely.
Please modify the condition above, and see the power amplifier is operating cooler than before. If you have other questions, please let me know.
Best,
Raymond
