AMETEK DCS-E 3kW Series - Manual (Page 79)

Sorensen DCS-E Series 3kW Supplies Theory of Operation
M362295-01 Rev C 5-9
The current control circuit consists of op amp U3-C and its related components. Operation of
the current control circuit is similar to that of the voltage control circuit. The 0-5V output current
feedback signal from the A4 shunt amplifier is monitored at the inverting input of U3-C (pin 9).
The 0-5V reference signal, from either the front panel control (via analog gate U3-D), a remote
analog programming source (via analog gate U3-A), or an IEEE-488 programming card (via
resistor R77), is monitored at the non-inverting input (pin 10).
Resistor R45 and diode CR17 "OR" the output of the voltage and current control circuits to
derive the A3 PWM and A4 down programming control signal. During voltage mode operation,
the output of the current control circuit remains high and the output of op amp U3-D provides the
control signal through diode CR17. During current mode operation, the output of the voltage
control circuit is high, diode CR17 is reverse-biased, and the output of op amp U3-C supplies
the control signal through resistor R45. The control signal regulates the output of the supply by
providing negative feedback to the A3 PCB PWM error amplifier. For example, if the power
supply output voltage or current attempts to rise above the selected level:
•
the control signal from the voltage and current control circuits decreases and
•
causes the output of the PWM error amplifier to decrease, which
• reduces the output pulse width from the PWM, and
•
reduces the voltage and current output to the selected level.
A complementary reaction occurs if the power supply output attempts to fall below the selected
output. The control signal, error amplifier, and PWM output pulse width all increase to raise the
output to the selected value.
Op amp U3-B monitors the voltage across diode CR17 to control the voltage and current mode
indicator LEDs on the front panel of the supply. When the supply is operating in voltage mode,
diode CR17 is forward-biased, the output of U3-B is high, and the voltage mode LED is
illuminated. When the supply is operating in current mode, diode CR17 is reverse-biased, the
output of U3-B is low, and the current mode LED is illuminated. In addition to controlling the
front panel mode LEDs, op amp U3-B also provides an analog remote monitoring signal at J3
connector pin 5 and a readback signal for the optional IEEE-488 card at pin 6 of connector P2.
The internal shutdown/soft start circuit is made up of MOSFET Q1, capacitor C3, diode CR3,
and resistors R2 and R3. The circuit is activated by the remote shut down, OVP,
over-temperature shutdown, and sense line protection circuits, as well as by the front panel
standby switch. When any of these circuits are activated, a high signal is applied through diode
CR3 to charge capacitor C3 and turn ON Q1. This clamps the reference input for the voltage
control circuit at pin 12 of U3-D to ground and causes the output of the supply to fall to zero.
When the shutdown condition is removed, capacitor C3 discharges through resistors R2 and R3
and the voltage control reference at pin 12 makes a controlled rise.
R EMOTE /L OCAL P ROGRAMMING S ELECT C IRCUITS
These circuits select the source of the voltage and current control circuit reference signals. The
reference signals are provided by one of three sources:
•
Front panel controls (local programming mode)
•
Remote analog programming sources
•
Optional IEEE-488 programming card