AP-10: “C” Product Notes
download as PDF
UltraVolt's “A” Series units are designed for DC-bias applications
with feedback compensation
optimized for dynamic loading. Multiple tuned and untuned LC and RC filters
provide low ripple
without a need for external capacitors. “A” Series units are
applicable to low-speed, capacitor-charging
applications. When calculating Trise, the output charge current available
is 66% of rated
lout and capacitance-to-charge should have the “A” Series unit's
internal capacitance added.
UltraVolt's “C” Series units are designed
specifically for pulsed loads and high-speed charging of
small and large capacitive loads. DC and AC feedback loops are compensated
to provide fast
rise time with low overshoot. Current-limit circuits are enhanced to get
in and out of limit as fast
as possible to maintain high average charge currents while protecting the
supply (HVPS) power stage. When calculating “C” Series Trise,
the output charge current
available is 100% of rated lout. “C” Series units have ½ to
1/10 of the filter capacitance of “A”
Series units, allowing more energy to go to the load capacitance (see Fig.
F in the “C” Series
datasheet). When using a “C” Series unit in a DC-bias application,
an external capacitor is
recommended for filtering.
Note: CAP LOAD MUST RETURN to HV
Ground Return (pin 8).
If the HVPS is to be grounded to the case, it should also
be grounded via pin 8.
Using Enable/Disable (pin 4) to activate the power supply
after input power has been applied permits the user to use TTL logic to
control HV outputs, (i.e. “1” state
= ON, “0” state = OFF).
This can be helpful in setting up redundant interlocks or shutting off
the HVPS prior to firing a
high-energy load. It also acts as an easy method to measure rise time by
oscilloscope external sweep trigger input to the Enable/Disable (pin 4)
prior to generating a
positive “1” rise command (see Application
Rise times are measured from start of discharge to the
time required to rise within 99% of final
regulated output. All rise-time data, however, is taken at +24VDC because
sources have somewhat different effects on rise time/overshoot (depending
on capacitive load used).
The rise time required to charge an external capacitor
load (CL) can be computed in accordance
with the formula shown below:
(CL + CINT)
T = Rise time in milliseconds to within 1% of final value (using an enable
CL = External load capacitance in micro farads
CINT = Internal supply capacitance (see UV HVPS
datasheet Fig. F)
Volts = Voltage in volts to which the capacitor is charged, starting from
Ishort = The output current of the “C” Series
power supply in milliamperes when measured under
output short-circuit conditions.
HIGH CURRENT PULSED APPLICATIONS:
In cases when large transient discharges of small duration are applied
to the output of a “C”
Series unit, the user may wish to isolate the “C” Series power
supply from the load CL. This is
typically done to place a more average current demand on the high-voltage
keeping peak currents below the HVPS current-limit point. This allows the
HVPS to provide the
maximum average power to the load by adding a filter cap directly across
the HV Output (pins 10 & 11) and HV
Ground Return (pins 8 & 9). A 10Ω to 1kΩ resistor
can then be added between the
HV output and the load CL. This will also reduce the tendency to introduce
overshoot in the
output waveform, which could cause a ringing on the HV output when driving
certain types of
loads (see diagram below).
Note: The energy-storage capacitor and the isolation resistor
droop" during high-discharge-current
conditions and average the peak current, thereby reducing the amount of
time the HVPS is in peak current limit.
*** END OF APPLICATION NOTE #10 ***