DEC VT220 - Page 192

• +12 V output circuit containing a rectifier (0510), and
filter networks (R508 and C520, and T503, C511, C512, and
C518).
• Sensing resistor (R~07).
DC outputs are generated from T501 secondary potential~ and output
to the logic board (via J2), monitor circuits, and the dc ok
circuit. In addition, +12 V, along with an output from the +5 V
circuit, is sent to the pulse width modulator, and +5 V, along
with the sensing resistor potential, is sent to the overcurrent
protect circuit. These outputs are monitored to control the pulse
width of the T501 primary potential to compensate for any
overvoltage, undervoltage, or overcurrent condition.
Table 9-2 provides specifications for the three dc outputs.
Table 9-2
Output Voltage Specifications
Voltage
+5 V
Specification
Nominal output
Mi n imum load
Maximum load
Ripple
Noise
Total regulation
Static line reg.
Static load reg.
Long term stability
Thermal Drift
Dynamic load reg.
Overload protection
Value
+5.0 V
1 A
2.2 A
150 MV p-to-p for < 66 KHz (max)
(see note 1)
1% of peak for> 100 KHz (noise is
superimposed on ripple) (see note 1)
+5.0%
+5.0%
+5.13%
3.1%/1000 hr (see note 2)
+0.025% per degree centigrade (see
note 2)
+2.2%
(see note 3)
Current limit with foldback (limit
point of 6.5 A max. and foldback at
3.3 A max.)
NOTES:
1. Ripple and noise must be measured with wide band oscilloscope
such as Tektronix P6046 differential probe, with scope set for
>100 MHz bandwidth, and specification applies only to
repetitive voltage variations occuring while operating with
constant input voltage and fixed load.
2. Long term stability and thermal drift specifications apply
after five minute warm up and are measured at the dc
distribution buses with an averaging meter.
3. Dynamic load regulation is measured in +25% load steps from a
starting point of 75% of full load, with measurements made at
power suppy terminals.
9-9