AP-10: “C” Product Notes
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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 high-voltage power 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 connecting the oscilloscope external sweep trigger input to the Enable/Disable (pin 4) prior to generating a positive “1” rise command (see Application Note #1).


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 different input-voltage 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:

T =
(CL + CINT) Volts

T = Rise time in milliseconds to within 1% of final value (using an enable command)
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 0 volts
Ishort = The output current of the “C” Series power supply in milliamperes when measured under output short-circuit conditions.


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 power supply, 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 control "pulse droop" during high-discharge-current
conditions and average the peak current, thereby reducing the amount of time the HVPS is in peak current limit.

Rev. D1