Filter
Top Products
1-2
1-5. Over-current Protection
In S6V and +6V lines, the voltage drop owing to the
current flowing in L203 is detected by pins 5 and 6 of
IC401, when the total current amount exceeds 8A, pin 7
develops high and the voltage biasses the base voltage of
transistor Q401 passing through the zener diode D402
and diode D401. In the same way as described in the
item of the over-voltage protection, IC303 is latched and
all outputs are shutdown. The method to release the latch
operation is the same as the item of the over-voltage
protection.
Over-current protection at +10V, +13V, +15.5V lines are
carried out by the over-current protection characteristic
provided with the series regulator ICs (IC203, IC202 and
IC201). Refer to Fig. 1-5-1.
In this case, as only the line short-circuiting or overload-
ing is protected, no effect appears on other outputs. The
protection is released by removing the over current
flowing condition.
When short-circuiting or overloading continues, the IC
overheats and the overheat protection circuit inside the
IC works to shut down the output voltage. In this case,
the overheat protection is released by unloading the
current and removing the overheat of IC.
Fig. 1-5-1
<Supplement>
The over-current protection for lamp output detects the
voltage drop of the current detection resistor R113 at
between pins 9 and 10 of IC302. When voltage switching
terminal of connector C opens (at 16.3V), the photo
coupler PH303 turns off since pin 1 of IC401 develops
low and the voltage of drop voltage at R113 is directly
compared at pin 10 of IC302. When the lamp output
current is from 0.7 to 0.9A, pin 8 develops high and the
voltage higher than 7V is added to pin 6 of IC303. Then
IC303 is latched and all outputs are shut down.
When the voltage switching terminal of connector C
develops the ground potential (at 18.0V), pin 1 of IC401
develops high, PH303 turns on and the voltage of drop
voltage at R113 and the voltage divided by R317 and
R327 are compared at pin 10 of IC302. When the lamp
output is from 1.05 to 1.35A, pin 8 of IC302 develops
high, IC303 is latched and all outputs are shut down. The
method to release the latch operation is the same as the
over-voltage protection description.
1-6. Overheat Protection
As an overheat protection of the power supply, the
temperature of switching FET Q301 of the boost-up-
converter is detected. Positive characteristic thermistor
TH301 for temperature detection is attached on the heat
sink of Q301. When Q301 is overheated owing to the
overload and/or defect of cooling fan, etc., the resistor
value of TH301 increases abruptly, while the surface
temperature exceeds approx. 120°C. Then the transistor
Q302 turns on, the voltage higher than 7V is added to the
pin 6 (OVP) of IC303, IC303 is latched and all outputs
are shut down.
When releasing the latch operation, stop to supply the
commercial power by canceling, cool enough after more
than approx. 120 seconds, and then re-supply the
commercial power.
100
80
60
40
20
0
0 1.0 2.0 3.0 4.0
Output current Io (A)
Relative output voltage (%)