In some of the embedded applications, we see a need for negative voltage requirement. One of the cases is like reference voltage generation that can be used for the negative terminal of the operational amplifier. One can understand that the case of a negative supply for the operating amplifier requires less current (not more than 2-3mA).
Flying Capacitor Voltage Converter is one of the circuit used to generate the negative voltage from the positive input. The construction of the circuit is as follows:
- 4 switches are present in the circuit
- Switch-1 and Switch-2 have inputs of positive supply input and ground respectively
- A polarized capacitor is connected at the output of Switch-1, Switch-2
- The capacitor on the other end has Switch-3 and Switch-4
- Another polarized capacitor with inverted polarity is connected from output of Switch-4 to ground
The functionality of the circuit is as follows:
- After the Input power is switched on, the level applied to Switch-1 and Switch-2, switches them ON
- The capacitor charges from the input supply to it's level
- Under this state, the Switch-3 and Switch-4 are OFF
- Under the next pulse state, Switch-1 and Switch-2 shall be OFF
- Switch-3 and Switch-4 shall be ON under this state and charged capacitor discharges
- The charge is built up slowly in the output capacitor and is seen as a negative voltage on it's terminal
One of the major disadvantage of this circuit is that the load cannot exceed beyond 1-2mA and depends on the output capacitor capacity. While this is a very simple circuit, in practical circuit requires several other supporting components to have a fixed negative voltage.
]]>
0 Comments