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1.2.4
Protection circuit
A fuse is inserted in the 12V line (F910, F911) as an overcurrent protection and as a circuit
that maintains the oscillator output at the LOW level and stops the power circuit operation
when the overvoltage protection (OVP) circuit or overheat protection (TSD) circuit operate.
1.2.4.1.
Latch circuit
This circuit maintains the oscillator output at the LOW level and stops the power circuit opera-
tion when the overvoltage protection (OVP) circuit or overheat protection (TSD) circuit operate.
The latch circuit holding current is 70µ A max. (Ta = 25˚C) when the voltage of pin
By considering that this increases lightly at high temperatures and by passing a current of
140µ A or more to the pin
stopped state. A delay time is provided with C2 in the hybrid IC to prevent malfunctioning by
noise, etc. If the OVP or TSD circuit operation continues for approx. 10µ sec or more, the
latch circuit will operate.
Note that even if the latch circuit operates, the constant-voltage power (Reg) circuit is function-
ing in the control circuit, and the circuit current is high. Thus, the voltage of pin
suddenly. When the voltage of pin
the circuit current will drop to 70µ A (Ta = 25˚C) or less, so the voltage of pin
rising.
When the operation start voltage (17.6V (typ.)) is reached, the circuit current will start to in-
crease again, so the voltage of pin
ating, the voltage of pin
vent the voltage of pin
during latch circuit operation is shown in the figure below. The latch circuit is canceled by
lowering the voltage of pin
power OFF and ON.
(TYP)
(TYP)
1.2.4.2
Overheat protection circuit
This circuit operates the latch circuit when the hybrid IC's frame temperature exceeds 135˚C
(MIN). The temperature is actually detected by the control circuit element. Since MOSFET
and the control circuit element are on the same frame, this will also function when MOSFET
overheats.
from the starting resistor, the power circuit will maintain the
drops to below the operation stop voltage (10.1V (typ.)),
will drop suddenly. Thus, when the latch circuit is oper-
will rise and lower between 10.1V (typ.) and 17.6V (typ.) and pre-
from rising higher. An example of the voltage of pin
to less than 7.9V, and generally, it is restarted by turning the AC
4
Example of waveform of pin
at latch circuit operation
1 - 6
is 10.5V.
will drop
will start
waveform
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