I have been working with the LM2907 as I have been designing a few circuits around it. This has lead to me wanting to understand more of its inner workings and build up a breadboard model of the internal circuit. The reason for not just using the chip is I need to display the relative key functions.
Is there possible errors in the below schematic? Specifically:
- Charge Pump
- The use of
Q2to charge the
22nFwhich is in the external area
- My choice of
C1, being electrolytic
Below is the schematic referring to the question:
How I believe it should work:
The comparator (IC1A) would turn the input frequency into the correct "pulse" to the Charge Pump.
The Charge pump is based off of a single stage charge pump model. I placed
Q2 so as to charge
C2 as would the LM2907 do.
After this it would go to the OP-AMP, aside LM741 is used but could be any, which will control the output resistor
Q1 with feedback to the Inverting input from the emitter.
These are images from the datasheet. The first is the circuit to which the above is meant to mimic in operation(less components for visibility).