PRINCIPLES OF OPERATION
REV.-A
EA1 and EA2 in the IC are error amplifiers. EA2 is used to detect the output voltage. Figure 2-27 illustrates
the setting of the output voltage. The rated voltage of Zener diode ZD23 is 5 V. Accordingly, 5 V is input
at the negative terminal of EA2.
The error amplifier works to bring the voltages at the positive and negative terminals into conformance. Voltage
is output, when necessary, to bring the voltage at the positive terminal to 5 V.
Figure 2-28 shows the EA2 output conditions. If the voltage of pin 16 becomes higher than that of pin 15
(i.e., if over-voltage occurs), EA2 begins output. PWM is activated on the basis of the output level, and the
circuit’s output voltage is lowered. (Further details are provided subsequently.)
20µs/DIV
Figure 2-26. Oscillator Waveforms
output
Voltage
+
Figure 2-27. Constant Voltage Control
Under Voltage
;
Over Voltage
EA2
output
(NORMAL Voltage)
I
Figure 2-28. EA1 Output
2-22
LQ-510
To Next Page
Loading...
