Dc-Dc Power Converter; Ac Control Logic - Ametek i Series User Manual

User Manual

5.6 DC-DC Power Converter

The DC-DC power converter, A3, is powered from the rectified AC input. The converter is a
PWM (pulse width modulated) full bridge type that uses IGBT‟s as the power switches. The
control logic supply for the DC-DC converter is derived from the auxiliary power supply so the
DC-DC converter does not start switching until after the auxiliary power supply has started up
and comes into regulation. This feature ensures a smooth start up.
The output of the DC converter is automatically selected for 250 VDC or 500 VDC output
depending on whether the low range output (135/150 Vac) or high range output (270/300 Vac) is
selected. The 250/500 VDC range selection is made by a relay that selects one of two taps on
the DC output transformer. The converter is fully protected with input current limit and
overvoltage protection. When the output of the DC converter is up and in regulation, the LED on
the input/output board will be lit. The LED can only be seen by looking directly down between the
large storage capacitors and the input/output board. (See Figure 5-3)

5.7 AC Control Logic

The main function of the control board, A4, is to generate the gate drive signals for the AC power
stage. This board also includes the circuit for the current limit and when two or three units are
operated in parallel, the load sharing circuit. (See Figure 5-6)
The signal from the oscillator is fed through a low pass filter circuit and sent to the reference
input of the error amplifier. The voltage output of the unit is differentially sensed and fed back to
the error amplifier thereby completing the control loop. The output of the error amplifier drives a
37.5 kHz pulse width modulator. The modulator output is sent to four gate drivers which drive
the IGBT‟s on the AC power board after going through opto couplers that provide the necessary
isolation.
106 i Series / iX Series