Switching Power Supplies A - Z

Chapter 7

Figure 7-11: Combining Blocks and Thus Showing That “Open-loop” Gain Is

Actually in a Closed Loop

The Voltage Divider

The output V

O

of the power supply first goes to a voltage divider. Here it is in effect,

just stepped-down, for subsequent comparison with the reference voltage ‘V

REF

.’ The

comparison takes place at the input of the error-amplifier, which is usually just a

conventional op-amp (voltage amplifier).

We can visualize an ideal op-amp as a device that varies its output so as to virtually equalize

the voltages at its input pins. Therefore in steady state, the voltage at the node connecting Rf2

and Rf1 (see “divider” block in Figure 7-10 ...