參數(shù)資料
型號(hào)： UPC29S78
英文描述： Useage of Three-Terminal Regulators | User＇s Manual[05/2000]
中文描述： 使用三端穩(wěn)壓器|用戶手冊(cè)[05/2000]
文件頁(yè)數(shù)： 3/35頁(yè)
文件大小： 187K
代理商： UPC29S78
User’s Manual G12702EJ8V0UM00
11
<8> Overheat protection circuit
The overheat protection circuit prevents destruction of the IC by cutting off output if the temperature of the
chip itself increases too much.
Figure 3-5 shows the parts of an overheat protection circuit. Q12, which is biased to the extent that it is not
ON in a normal operating state, is completely ON at 150
°C to 200°C accompanying a decrease in VBE when
the temperature of the chip increases. When Q12 is ON, it cuts off the output voltage by absorbing the base
current of the output stage power transistor.
Figure 3-5. Example of Overheat Protection Circuit (
PC7800A Series)
Q17
Q12 : Overheat protection
transistor
Q16
OUTPUT
INPUT
GND
The overheat protection circuit is designed to operate at temperatures exceeding the absolute maximum
rating (generally 150
°C). Therefore, if the overheat protection circuit has operated, the IC should be
considered to have been exposed to an abnormal state and positive use of the overheat protection circuit
should be avoided (so a separate circuit is needed to perform power supply overheat protection).
3.2 Operating Principles of Adjustable Output Types
An adjustable output type (
PC317, PC337) differs from a fixed output voltage type in that it uses a method for
configuring an output voltage setting voltage circuit externally so that an arbitrary output voltage can be set
externally.
Figure 3-6 is the block diagram of a variable output voltage type. The output voltage is controlled by comparing
the voltage between external resistors RA and RB and the reference voltage VREF in the error amplifier.
Moreover, each block is connected between INPUT and OUTPUT and the current needed in each block (circuit
operating current) is output from the OUTPUT pin.
Therefore, the outflow current from the ADJ pin becomes
negligible and its affect on the output voltage value can be ignored.
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