--SOLVED--
I have implemented a PWM control over a relay from an Arduino. To isolate both circuits I have used an optocoupler 4N35 from Vishay. Since it cannot provide enough current flow to drive the relay, I have used a BC548B transistor creating a Darlington structure with the internal output transistor of the 4N35.
The problem is that I have simulated the circuit but then, when I try to calculate the currents in the circuit I am unable to achieve the simulated values. I don't know how to achieve the \(V_CE(OK3)\) neither \(I_F\).
I hope you can guide me.
Salus
Moderators note: removed the plains from the post
I have implemented a PWM control over a relay from an Arduino. To isolate both circuits I have used an optocoupler 4N35 from Vishay. Since it cannot provide enough current flow to drive the relay, I have used a BC548B transistor creating a Darlington structure with the internal output transistor of the 4N35.
The problem is that I have simulated the circuit but then, when I try to calculate the currents in the circuit I am unable to achieve the simulated values. I don't know how to achieve the \(V_CE(OK3)\) neither \(I_F\).
\(I_{K1} = \frac{+12V_{PS2}-V_{CE(Q4)}}{K1}\)
\(I_{K1}=\frac{I_{C(Q4)}}{\beta _{Q4}}\frac{\beta _{OK3}}{(\beta _{OK3}+1)}+I_{C(Q4)}\)
\(V_{CE(Q4)}=V_{CE(OK3)}+V_{BE(Q4)}\)
\(P_{OK3}=I_FV_D+I_{C(OK3)}V_{CE(OK3)}\)
\(P_{Q4}=I_{C(Q4)}V_{CE(Q4)}\)
Even if I've checked the 4N35 datasheet, I am unable to calculate the values for my circuit. The \(V_F\) for the input diode is only expressed by a fixed current of 10 mA. Then, I am unable to know what will be the \(V_CE(OK3)\) and therefore I cannot achieve the \(V_CE(Q4)\). Summarizing, I have nothing.\(I_{K1}=\frac{I_{C(Q4)}}{\beta _{Q4}}\frac{\beta _{OK3}}{(\beta _{OK3}+1)}+I_{C(Q4)}\)
\(V_{CE(Q4)}=V_{CE(OK3)}+V_{BE(Q4)}\)
\(P_{OK3}=I_FV_D+I_{C(OK3)}V_{CE(OK3)}\)
\(P_{Q4}=I_{C(Q4)}V_{CE(Q4)}\)
I hope you can guide me.
Salus
Moderators note: removed the plains from the post
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