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REV.-A
EA 1 and EA2 in the le are error amplifiers. EA2 is used to detect the output voltage. Figure 2-16
illustrates the setting of the output voltage.
The rated voltage of Zener diode ZD23 is 5V. Accordingly, 5V 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 5V.
Figure 2-17 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).
o
20lls/DIV
Figure 2-15. Oscillator Waveforms
Output
Voltage
V
(NORMAL Voltage)
I
I
I
I
I
I
I
16Pin
15Pin
Over Voltage
EA2
Output
Figure 2-16. Constant Voltage Control
Figure 2-17. EA1 Output
2-19
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