DIY Intercom Design Thread 5

This time it is using the IC made by National Semiconductor the LM2662M. This is a direct replacement for the MAX1044 just it is a surface mount part (so it is a lot smaller). I have also changed the main voltage regulator to the LM7805ACT, more on this later. This circuit is connected to a DC power supply such as a battery or an automotive altern
DIY Intercom Design Thread 5 - schematic

ator/battery. The first thing the power hits is the LM7805ACT. This is a 1A +5v voltage regulator. The voltage regulator allows an input voltage of +7v up to +35v, so this CAN run off of the 24v systems in aircraft too! The LM7805ACT is different than the common LM7805CT. The CT version has an Output Voltage Tolerance of +/- 4%, where as the ACT version (the one we are using) has an Output Voltage Tolerance of +/- 2%. Basically the voltage coming out of the ACT version is cleaner than the CT. Price difference on the two is only $0. 40, so I would rather have the better quality one. Coming out of the LM7805ACT is a +5v supply. We need to invert this so we can have a -5v supply for our microphone pre-amplifier IC`s. This is done using a Switched Capacitor Voltage Converter, the LM2662M. This circuit is just like the MAX1044 IC that I was using earlier. "The LM2662M CMOS charge-pump voltage converter inverts a positive voltage in the range of 1. 5v to 5. 5v to the corresponding negative voltage. The LM2662 uses two low cost capacitors to provide 200 mA of output current. With an operating current of only 300 A and operating efficiency greater than 90% at most loads, the LM2662 provides ideal performance for battery powered systems. " (taken from the LM2662 White Paper) So, in conclusion the LM7805ACT allows 1 amp of current on the +5v supply line and the LM2662M allows 400mA of current on the -5v supply line. The current draw...

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