DC891A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 891
HIGH CURRENT CAPACITIVE CHARGING CIRCUIT
LT3750EMS
DESCRIPTION
Demonstration circuit 891 is a High Current Capacitive Charging Circuit featuring the LT3750EMS. It is a
DC/DC flyback converter used to charge large capacitors to high voltages. The circuit implemented on
the board is a simple example of how to charge a
400uF capacitor to 300V in approximately one second, depending upon the line and load conditions.
An output capacitor discharge circuit is included on
the board for the convenience of the user. This discharge circuit can be disabled by the user or permanently enabled at the expense of a minor degradation
in the charging profile.
there is no need to connect components to the high
voltage output. The charging current is set by an
external sense resistor and is monitored on a cycleby-cycle basis. The LT3750 is available in a space
saving MSOP-10 package.
The LT3750 is a current-mode flyback controller optimized for charging large value capacitors to a predetermined target voltage. This target voltage is set
by the turns ratio of the flyback transformer and just
two resistors in a simple, low voltage network, so
Design files for this circuit board are available.
Call the LTC factory.
WARNING! LETHAL VOLTAGES ARE PRESENT ON
THE DC891 CIRCUIT BOARD. DO NOT OPERATE
THE ASSEMBLY UNLESS YOU ARE TRAINED TO
HANDLE HIGH VOLTAGE CIRCUITS.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Input Voltage Range
Vout = 0 to 320V
6-20VDC
Output Target Voltage
Vin = 6 to 20VDC
300 + 5%VDC
Average Input Charging Current
Vin = 0 to 20V, Cload = 400uF
2.2A
QUICK START PROCEDURE
WARNING! LETHAL VOLTAGES ARE PRESENT ON
THE DC891 CIRCUIT BOARD. DO NOT OPERATE
THE ASSEMBLY UNLESS YOU ARE TRAINED TO
HANDLE HIGH VOLTAGE CIRCUITS.
1.
With the power source turned off, connect the input power supply to the board through the VIN
(E1) and GND (E2) terminals.
2.
Connect the load to the VOUT (E3) and GND (E5)
terminals.
Demonstration circuit 891 is easy to set up to evaluate the performance of the LT3750. For proper
equipment setup, follow the procedure below, referring to Figure 1.
3.
Set the CHARGE jumper at JP1 to the STOP position. Alternatively, the user may connect a 0-24V
signal source to the three pin JP1 header. Refer to
the data sheet and schematic for proper signal levels.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 891
HIGH CURRENT CAPACITIVE CHARGING CIRCUIT
4.
5.
Position the OUTPUT BLEEDER jumper at JP2 to
the NORMAL OPERATION position for initial testing. The user can also leave the jumper set to
DISCHARGE, but there will be a minor degradation
to the operation of the charge time.
6.
Change the CHARGE jumper at JP2 to the GO position. If a signal source is used, apply an active
transition.
7.
The output should start charging towards 300V.
Turn on the input power source to at least 6V, but
below 20V.
OPERATION
WARNING! LETHAL VOLTAGES ARE PRESENT ON
THE DC891 CIRCUIT BOARD. DO NOT OPERATE
THE ASSEMBLY UNLESS YOU ARE TRAINED TO
HANDLE HIGH VOLTAGE CIRCUITS.
Demonstration circuit 891, featuring the LT3750, is a
DC/DC Flyback converter used to charge large valued
capacitors to a predetermined voltage. The charging
current is set by the current sense resistor R10, while
the target voltage is determined by the turns ratio of
the transformer T1. For a complete description of the
operation of the LT3750 integrated circuit, please refer to the data sheet.
The DC891 demo board is equipped with two physical
interfaces to control the charge cycle. One is a simple solder terminal at location E6. The other is 2mm
header at location JP1. For the convenience of the
user, a high impedance 100K pull up resistor is connected between the CHARGE pin and the VIN power
input. A jumper has been installed between CHARGE
and GND. The data sheet defines a signal profile that
must be used to properly activate the CHARGE input,
so it is recommended that the user employ a suitable
signal source to control the charge cycle.
The DONE bit is pulled up to VIN through a high impedance 100K resistor. This may not be compatible
with all electrical systems.
DC891 is equipped with a safety circuit that drains the
output capacitor of charge when the controller is not
delivering energy to the load. When JP2 is set to
NORMAL OPERATION, this safety circuit is disabled
and the output capacitor will bleed down from its own
leakage current. If JP2 is set to DISCHARGE, the
output capacitor will be discharge through the combined parallel resistance of R2, R3 and R4.
Due to the high charging currents made possible by
the LT3750, it is possible to simply engage the safety
circuit all the time by leaving JP2 in the DISCHARGE
position. This will result in only a minor degradation
in the charging profile.
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 891
HIGH CURRENT CAPACITIVE CHARGING CIRCUIT
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 891
HIGH CURRENT CAPACITIVE CHARGING CIRCUIT
4
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