VPSB-DC and VPSB-DC-E
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15.4.1 Control FPGA
The control FPGA receives commands (e.g. desired output voltage) from the ELCB via the
backplane SSRB. The FPGA reads from the Analog-to-Digital converters and controls the
voltage of the power stages of the variable power supplies.
15.4.2 Power Supply and Output Power Control
The total output power of the VPSB-DC is limited to 280 W by the input power DC/DC
converter. Each heater channel can deliver up to 250 W, provided that the total power does
not exceed 280 W. The BSVT makes the power budgeting by using and limiting the set
maximum powers of the two channels, i.e. the two maximum powers added together are not
allowed to exceed 280 W.
For the VPSB-DC-E, a booster is available on the first output channel. The BSVT
automatically switches on the booster, if the maximum power of channel one is set to a value
above 250 W. Without booster, there are the same limitations to the output power as for the
VPSB-DC. If the booster is enabled, the output power of channel one is equally distributed
between the VPSB-DC part of the board and the booster extension part, with the following
implications on the maximum output power: Only half of the first channel‘s power flows into
the maximum power calculation.
For example, if the first channel maximum power is set to 400W, there is still 280 W – 400
W / 2 = 80 W available for the second channel. Vice versa, if the second channel maximum
power is set to 100 W, the first channel power is reduced to (280 W-100 W)*2 = 360 W.
The AV4 BSVT software will handle the power budgeting such that the currently changed
maximum power has priority, i.e. the other channel‘s maximum power will be automatically
reduced if the budget would be exceeded.
If the booster is enabled (maximum power setting > 250 W), a small offset voltage in the
order of a few 100 mW will be seen on the output, even if the target voltage/power is set to
zero.
The output of a VPSB-DC(-E) channel is enabled whenever a temperature regulator is
operating. The two power stages can be enabled independently.
The booster can only be switched on and off if the VPSB-DC-E channel one is off. It is
therefore only possible to set the maximum output power above 250 W if the temperature
regulation is switched off.
Before the output power is enabled, the load resistance is measured by dedicated electronics
with high precision. Afterwards, during actual VT operation, output current and voltage are
measured and monitored. For a specific heater power, the voltage is evaluated based on the
initial load resistance. If the load resistance changes significantly during operation (e. g.
broken lines, contact problems, material faults) then the BSVT switches off and issues an
error message.
The registers for output power commands are self-clearing. A control instance must therefore
update the output parameters at regular intervals, otherwise the outputs are reset by a
watchdog circuitry for safety reasons.
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General