GENERAL INFORMATION:
The “AA” Series of high-voltage regulated
DC-DC converters addresses the needs of the miniature
PCB-mount regulated high voltage power supply
user. Designed and built utilizing state-of-the-art
power-conversion topology, these units feature
surface-mount technology and encapsulation techniques
that provide high reliability and low cost.
DESIGN METHODOLOGY:
The “AA” converters utilize a dual-ended forward
converter topology with a nominal switch frequency of <100kHz.
A precision reference is provided so the remote control can program
the power supply for a specific voltage. Once input voltage stabilizes,
under-voltage lockout is released. As soon as enable is raised above a
TTL 1, the converter begins to switch. The soft-start circuit brings
the converter to full power over a 1mS period, reducing surges on the
source supply. A constant-frequency PWM regulation system controls the
MOSFET push-pull power stage which drives the high-voltage transformer.
The power stage is protected from output-current overloads or short
circuits via a secondary current-limit circuit. High voltage is developed
by a multistage multiplier, while feedback voltage is developed and sent
to the CTRL circuit to maintain regulation. Internal filters are provided
to reduce input-current ripple and output-voltage ripple.
WIDE INPUT RANGE:
The “AA” Series is designed for full power operation at up to 90%
efficiency. A wide input range of +11 to +16VDC or +23 to +30VDC will maintain
full power output without derating. The derated input range is +9 to +32VDC.
See Application Note 16 for protection information.
WIDE OUTPUT RANGE:
The “AA” Series is a non-isolated,
unipolar converter. Positive or negative output
must be specified. Output voltage is adjustable
from 0 to 62V, 125V, 250V, 500V, 1kV, 2kV,
4kV, or 6kV. As the output voltage is reduced
towards 0, the maximum current capability remains
unchanged.
OUTPUT VOLTAGE MONITOR:
The “AA” Series features a voltage
monitor on pin 9 referenced to Signal Ground
pin 5. The scale factor is 100:1 on models
from 1kV to 6kV, and 10:1 on models below
1kV. The monitor output impedance is calibrated
for use with a 10-MegΩ input impedance
meter. Overall accuracy is ±2.0% with
a temperature coefficient of ±100
ppm per °C.
For
applications requiring a different scale
factor, such as an ADC-compatible design,
an external resistor may be added in parallel
with the output.
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OUTPUT CURRENT MONITOR:
The “AA” Series features an output
current monitor. Current from the high-voltage
multiplier can be monitored by reading the
voltage appearing between Output Monitor pin
3 and Signal Ground Return pin 5. Internal
voltage dividers create a small, compensable,
linear-offset voltage. See Application
Note 13.
REMOTE CONTROL:
The “AA” Series is remotely programmed
with 0 to +5 VDC to produce an output voltage.
Input may be from a control voltage, DAC,
variable or fixed resistor. On a negative
output converter, the programming logic of
the remote adjust would be inverted, i.e.:
+5 to 0VDC. Connections are on the converter
for the internal reference, analog remote
adjust, and the signal ground. The reference
is +5.0VDC, temperature-compensated with
a 464Ω output impedance. See Figure’s
E & F or Application
Note 1 for more
information.
STANDBY MODE:
The “AA” converters also have
an enable function. When the enable is TTL
0 (<+0.7V Isink=1mA), the converter is
in a standby mode and input current is reduced
to <30 mA. All functions other than the
internal reference are shut down. If the
enable pin is left unconnected, TTL 1, or
at greater voltages up to +32VDC the converter
operates normally. The open-circuit output
voltage from the Enable pin is <+5VDC.
In the inhibit/disable mode, 1 mA will have
to be sunk for proper shutdown.
MECHANICAL:
“AA” Series converters are in PCB-mountable plastic cases requiring
a footprint of 4.46 In² and only 3.35 In³ of volume. Mounting plates and brackets
are available for chassis mounting. See Application Note
6 for thermal considerations
and mounting configurations. All models are available with optional six-sided
wrap-around Mu-Metal Shielding.
ENVIRONMENTAL:
The “AA” Series provides full
power operation at case temperatures from
-40 to +65°C. All units receive a 24-hour
burn-in prior to final testing. Extended
temperature range is available along with
other enhanced capabilities. Please contact
the factory.
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