Toshiba TLP511E Руководство по техническому обучению - Страница 4

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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.

100

1.0

Output current Io (A)

Fig. 1-5-1

2.0

3.0

4.0

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.

1-2