Dear all,
Thank you very much for your help, I agree about the function of the circuit. Glancing the schematics and the article is enough to fully understand its functionality, where both isolators are coupling a PWM signal that is converted to its DC voltage later.
However, my question was specifically focussing on the pair of phototransistor which are working in "inverse mode" ( BOTH TRANSISTORS ARE NPN, WHOSE COLLECTORS DEAL WITH LOWER VOLTAGE THAN EMITTERS! )
The article says that you may use transistors in "inverse mode" in order to get a sub-millivolt VCEsat voltage, but It's really the first time I hear about reversing transistors -unless as an efficient way to burn them...- so I'd like to know about the transistor behavior in this configuration.
What's the BJT model when you swap emitter with collector ?
Thanks