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3DQDVRQLF
1.6.6 Latch Circuit
Latch circuit which sustains an output from the oscillator low and stops operation of the power supply
when over-voltage protection (OVP) circuit and thermal shutdown (TSD) circuit are in operation.
As the sustaining current of the latch circuit is 500
maximum when Vin terminal voltage is 4V, the
power supply circuit sustains the off state as long as current of 500
minimum flows to Vin terminal
from a start up resistor.
In order to prevent a malfunction to be caused by a noise and so on, delay time is provided by C1
incorporated in the IC and, therefore, the latch circuit operates when the OVP or TSD circuit is in
operation, or an external signal input is provided for about 10 or longer.
In addition, even after the latch circuit start operating, the constant voltage regulator circuit is in
operation and the circuit current is at high level. As a result, Vin terminal voltage rapidly decreases.
When Vin terminal voltage becomes lower than the shutdown voltage, VIN(OFF) (4.9V typical), it starts
increasing as the circuit current is below 500 .
When it reaches the ON-state voltage, VIN(ON) (8V typical), Vin terminal voltage starts decreasing
because the circuit current increases again.
When the latch circuit is on, Vin terminal voltage increases and decreases within the range from 4.9V
typical to 8V typical and is prevented from abnormally rising. Calibration of the latch is done by
decreasing Vin terminal voltage below 3.3V.
The power supply can be restarted after disconnecting an AC input to the power supply once.
1.6.7 Thermal shutdown circuit
It is a circuit to trigger the latch circuit when the frame temperature of the IC exceeds 150
(typical).
Although the temperature is actually sensed at the control chip, it works against overheating of the
power transistor as the power transistor and the control IC are mounted on the same lead frame.
1.6.8 Over-voltage protection circuit
It is a circuit to trigger the latch circuit when Vin terminal voltage exceeds 11V(typical). Although it
basically functions as protections as protection of Vin terminal against over-voltage, since Vin terminal
is usually supplied from the drive winding of the transformer and the voltage is proportional to the
output voltage, it also functions against the over-voltage of secondary output which causes when the
control circuit opens or in some other events.
1.6.9 Stand-by Mode TOP210
This IC(TOP210) is used for low-power consumption when receiver is operating in stand-by mode.
1-9-1 DRAIN PIN (pin5)
Output MOSFET drain connection. Provides internal bias current during start-up operation via an
internal switched high voltage current source. Internal current sense point.
1.6.10 CONTROL PIN (pin4)
Error amplifier and feedback current input pin for duty cycle control. Internal bias current during normal
operation. It is also used as the supply bypass and auto-restart/compensation capacitor connection
point.
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