User`s manual
OP7100 Hardware
25
Power Management
The OP7100 was designed to operate from a 12 V to 30 V DC source, and
consumes about 4.5 W with the backlight on, 1.5 W with the backlight off.
To allow for a surge current when the OP7100 is first turned on, the power
supply used must be able to handle at least four times this power (for
example, 800 mA at 24 V).
The OP7100 power supply is converted internally to supply three voltages.
1. A switching regulator outputs VCC (+ 5 V).
2. A linear regulator outputs VEE (approximately –20 V).
3. A high-voltage section supplies 300 V rms to drive the cold-cathode
fluorescent backlight. The backlight can be turned on or off under
software control whereby a high on the gate of Q3 enables Q1 and Q2 to
oscillate, and a low turns off Q3, stopping the oscillation of Q1 and Q2.
Figure 3-2 shows these internal power supplies in a block diagram
Figure 3-2. Block Diagram of OP7100 Internal Power Regulators
The DC input source can also be brought out on pin 9 of header J10, the
DE-9 connector, by installing a 0 Ω resistor at R32. This option allows
power to be supplied to a serial device connected to the OP7100 as long as
the serial device’s RS-232 port can handle the DC input on pin 9.
Be sure to use a power supply with sufficient capacity (for
example, 1.1 A at 24 V) to handle surges when the OP7100
and any devices connected to it are first turned on.
VCC
J10:9
1230 V DC
J11:5
1230 V DC
U28
2575
Sw Reg
U27
2951
Lin Power
U25
7662
Sw Reg
U23
7662
Sw Reg
VEE
VCC
2575
Sw Reg
Backlight
Power
from EPLD
300 V rms, 32.7 kHz,
to CCFL backlight
Q3