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Operation of the GRX, PVX-41XX and PVM-41XX pulse generators with common pulse (+HV) and bias (-HV) dc power supply polarities

Posted: 06 Sep 2001     Print Version  Bookmark and Share

Keywords:power 

/ARTICLES/2001SEP/2001SEP06_POW_HBM_AN.PDF

THE PULSE OF THE FUTURE

D I R E C T E D

E N E R G Y

I N C O R P O R A T E D

DEI's high voltage pulse generators designed for

driving high impedance and capacitive loads (the

GRX, PVX-41XX and PVM-41XX models) may

be operated with the pulse (+HV or VHIGH) and

bias (-HV or VLOW) DC power supply inputs at a

common polarity (i.e. -HV In at +500V and +HV

In at +1500V, or -HV In at -1000V and +HV In

at -500V).

However most high voltage DC power supplies

cannot regulate voltages of the same polarity

from a separate source. Positive power supplies

sink (draw) electrons from ground, while nega-

tive power supplies source (push) electrons to

ground. To operate with power supplies of com-

mon polarity, the lower voltage (-HV or VLOW)

supply must be provided with an additional cur-

rent flow path to ground. If this path is not pro-

vided, the output voltage may not remain at the

-HV In potential when the pulse generator is not

gated, but can be charged up to the potential of

the VHIGH (+HV In) supply due to leakage current

within the pulse generator. This is often ob-

served if the load does not draw current, or as

the pulse repetition frequency is increased.

The path to ground can be accomplished with a

shunt resistor (i.e. a resistor from the -HV In

power supply input to ground) in low power appli-

cations, or with an active shunt regulator for high

power applications.

To determine the value and size of the shunt re-

sistor, three things must be known:

1. The maximum pulse repetition frequency;

2. The maximum differential voltage (VHIGH -

VLOW);

3. Total load capacitance (including the load,

interconnect cable, and strays)

As the load is capacitive, what charge goes into

the load must also come out. The formula CV2

F

(where C is the total load capacitance, V is the

differential voltage between the VHIGH and VLOW

supplies, and F is the pulse repetition frequency)

provides the minimum power that must be dissi-

pated in the resistor or shunt regulator from

switching the capacitive load.

From the power calculated above, the discharge

current is calculated using the formula:

Operation Of The GRX, PVX-41XX and PVM-41XX Pulse Generators

With Common Pulse (+HV) and Bias (-HV) DC Power Supply Polarities

D I R E C T E D E N E R G Y , I N C . T E C H N I C A L N O T E

V

P

ABSTRACT

DC power supplies of the same polarity (i.e. both positive or both negative polarity) may be used for

the Pulse and Bias DC supply inputs of the GRX, PVX-41XX and PVM-41XX pulse generators. How-

ever most high voltage DC power supplies cannot regulate voltages of the same polarity from a sepa-

rate source. To operate with power supplies of common polarity, the bias, or lower voltage (-HV or

VLOW) supply must be provided with an additional current flow path to ground. If this path is not pro-

vided, the output voltage may not remain at the -HV In potential when the pulse generator is not gated,

but can be charged up to the potential of the VHIGH (+HV In) supply. This technical note describes how

to install a current path to ground to mitigate this problem.

THE PULSE OF THE FUTURE

Directed Energy, Inc.

2401 Research Blvd., Suite 108

Fort Collins, CO USA 80526

970-493-1901 Fax: 970-493-1903

Email: deiinfo@directedenergy.com

Web: http://www.directedenergy.com

Where P is the power calculated above and V

is the bias (-V) voltage .

For example, if the calculated power is 1W, and

the -V voltage is 100V, then the discharge cur-

rent is:

The value for the shunt resistor can be found

using the formula:

As this bias is not regulated and can vary with

operating parameters, a regulated power sup-

ply must be used to maintain a constant volt-

age. However if the power supply current in-

creases beyond the 10mA assumed maximum,

then the bias voltage will no longer be con-

trolled by the power supply. Therefore if the

bleeder resistor value is reduced by a factor of

2, then there will always be current drawn from

the bias power supply, and regulation will be

maintained. Hence in this example, a 5K re-

sistor would be chosen. DC current from the

VLOW DC supply will also flow in the shunt resis-

tor. This power can be calculated by the for-

mula:

Where V is the VLOW voltage, and R is the resis-

tance of the shunt resistor.

For reliability reasons, it is recommended that

power dissipation capability of the resistor be

doubled. Therefore in the example given

above, a 5K 5W resistor would be chosen.

In determining DC power supply requirements,

the VLOW (-HV In) DC power supply must be

able to provide the power dissipated in the

shunt resistor (2W, in this example), and the

VHIGH (+HV In ) DC power supply must be able

to provide the CV2

F power.

Please note that this potential problem does

not occur if the input DC power supplies are of

different polarities (i.e. -HV in t -1000V and

+HV In at +500V), or if one of the DC supply in-

puts is grounded (i.e. -HV In is connected to

ground and +HV In is at +1500V). Furthermore,

depending on the DC power supply used, at

low pulse repetition rates with small capacitive

loads, this problem may not be observed be-

cause of the small internal paths to ground

found within the DC power supply.

W

R

V

2

000,5

10022

==

Doc #9200-0208 Rev 1

) Directed Energy, Inc. 2000

mA

V

P

10

100

1

==

== 000,10

10

100

mA

V

I

V

R

HVPS

BIAS

SHUNT





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