Switching transistor's ohm between base and collector terminal

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siongboon

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Hi,

Attached is a circuit, which I believe its function is to re-condition a signal input.
There is a resistor 150kohm between the collector and emitter.

Do anyone knows what is the purpose of the 150kohm?
Also what is the purpose of having the 33ohm

Thank you very much.
Siong Boon
 

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The 150k is from collector to base. It is an amplifier. The 150k is setting the bias. The 33 ohms helps to set the gain, in conjunction with the emitter dynamic impedance and the collector resistor.

Keith
 

Of course, it is true what Keith has written - but you should know that both resistors not only set the bias point but, in addition, provide dc feedback thereby stabilizing the bias point.
However, it is a rather uncommon circuit because it mixes current with voltage feedback. The 150k resistor provides current feedback and the 33 Ohm resistor provides voltage feedback. But an effective voltage feedback needs a constant dc base voltage (versus ground) with respect to temperature changes. Normally, this is provided by a base voltage divider rather than by the shown 150k resistor.
 

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