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I don't think a Phototransistor is anything like an LDR. An LDR behaves like a resistor with a variable value. A Phototransistor behaves like a transistor and can look like an emitter follower or common emitter amplifier depending on how you connect it.
You could simply simulate with a swept resistor value. The only thing missing would be some capacitance.
I don't think a Phototransistor is anything like an LDR. An LDR behaves like a resistor with a variable value. A Phototransistor behaves like a transistor and can look like an emitter follower or common emitter amplifier depending on how you connect it.
The type of phototransistor I was thinking of is typically used either way below:
Similar to how a CdS cell is often used.
I didn't count the fact that a phototransistor can be sensitive and fast enough to serve as a high-speed switch (within reason).
Whereas a CdS cell responds more gradually, though still able to detect audio frequencies.
The problem is the depending on the circuit you cannot always put a phototransistor in place of an LDR where the circuit needs a resistance, not a voltage source. An example would be putting an LDR in the feedback of an opamp where the gain would change with light level. You could not easily substitute a phototransistor in that sort of circuit. Similarly you could put an LDR in place of one of the timing resistors in a 555 but not a phototransistor. It is easy to imply step or sweep a resistor value so I would have though that would have been the easy solution in most cases.
The problem is the depending on the circuit you cannot always put a phototransistor in place of an LDR where the circuit needs a resistance, not a voltage source. An example would be putting an LDR in the feedback of an opamp where the gain would change with light level. You could not easily substitute a phototransistor in that sort of circuit. Similarly you could put an LDR in place of one of the timing resistors in a 555 but not a phototransistor. It is easy to imply step or sweep a resistor value so I would have though that would have been the easy solution in most cases.
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