Keithley 7707, Руководство пользователя

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18
Source mode
When used as a source, current provided by the internal 5V supply flows out of the module to a load when the output line is set
high (logic ‘1’). Using an output line as a source provides control for low voltage, low current (up to 1mA) loads, such as logic
devices and indicator lamps.
Figure 14 shows how to use an output line to apply high and low logic levels to a NAND gate.
CAUTION Each output line can source up to 1mA. Exceeding 1mA may cause damage to the
Model 7707 that is not covered by the warranty.
Figure 14
Typical digital output—source mode
Digital I/O protection
Short circuit protection
Each digital output line has internal short circuit protection up to 25V. Over-current protection is tripped at approximately 1A.
A simplified circuit showing thermal protection for a digital output is shown in
Figure 15 .
In Figure 15 , a short circuit condition exists when the transistor switch for the digital output is closed (logic ‘0’). When the
current reaches 1A, the driver for the digital output automatically reduces the current to a level that will not damage the digital
I/O. If the short circuit condition is maintained, thermal limit circuitry senses the rise in device temperature and further
decreases the current.
CAUTION Short circuit protection is effective up to 25V. To avoid damage to the Model 27xx, DO
NOT apply >25V directly to a digital I/O line.
Model 7707
Ch 11 Bit 0
Ground
Channel 11 set
as output port
User Supplied Circuitry
Output
Control
(Ch 11 Bit 0)
Logic Device
NAND
B
A
Inverter
Logic ‘0’: Vout = 0V
Logic ‘1’:
>
2.4V = Vout =
≤
4.3V
Vout*
Note: Setting output line high (logic ‘1’) opens transistor switch to apply
logic high (’1’) to NAND gate.
Setting output line low (logic ‘0’) closes transistor switch to apply
logic low (digital ground) to NAND gate.
*
+5V