DEC VT220 - Page 188

• T50l transforms regulated ac input into secondary
voltages used by the dc output circuits to generate the
required dc potentials.
• DC output circuits -- generate the dc potential outputs
(+12 V, +5 V, and -12 V).
• Part of J2 are the pins of interconnection between piS
and monitor board and logic board used for routing of dc.
• Overcurrent protect monitors for +5 V/+12 V
overcurrent and +5 V overvoltage conditions.
• Pulse width modulator -- monitors overcurrent protect and
dc output circuits conditions to control width of ac
pUlses supplied to T50l by switching transistor network
within the input rectification circuit.
• T504 provides means for pulse width modulator to
control width of recti fed ac pulses supplied to T501.
Table 9-1 provides specifications for the ac inputs. Figure 9-4
shows the pinouts for J50l and J2. Each of the ac conversion
circuits are described separately (with the exception of
components J501, J2, T50l, and T504, which are discussed only as
they relate to the other circuits).
Table 9-1
Input Voltage Specifications
Voltage
115 Vac
Specification
Nominal voltage
Minimum voltage
Maximum votage
Input line current
Line frequency
Power factor
Inrush current
Peak inrush
Input power
Efficiency
Undervoltage
Overvoltage
Value
120 Vac
87 V
rms
134 V rms
1 A rms (max.)
47-63 Hz
(watts) -- (rms V X rms A) > 0.55
Surge current at first application
of input voltage may be reached for
1/2 cycle of input line, with
repetitive peaks of exponentially
decaying amplitude for up to 10 more
cycles.
25 A (Thermisters cold)
60 watts (max.) at full rated dc
output load of 40 watts.
0.65 (min.) output power to input
power ratio.
Provides minimum of 10 millisecond
hold-up at 90 V rms during power
outage.
150 Vac for 1 second (max.)
9-5