Thermal Comfort 3000 manual Switch-Mode Power Supply Operation, Switching Control PC Board

C. Switch-Mode Power Supply Operation

Primary three-phase power is rectified by the three- phase bridge diodes D1-D6. The resulting negative DC voltage (approximately -320 VDC) is applied to the switching transistor (Q1). The switching transis- tor controls the output current by pulse width modu- lation (PWM). PWM varies the duty cycle (or on-time versus off-time) of the switch. The greater the on-time, the higher the output current will be. Components D7-10, R2-3, C13-14, L1, and the Suppression PC Board are snubbers to limit voltage and current surges caused by switching Q1 on and off. D11-14 are free wheeling diodes. When Q1 is on, current flows through Q1 into the output network. When Q1 is off, D11-14 provide a path for current to continue flowing supported by energy that was stored in the output network during the time Q1 was on. The switching transistor output is a series of pulses which are filtered back into pure DC voltage by the output network. The output net- work consists primarily of the main inductor (L2A and L2B), resistor R13, and capacitor C23.

D. Switching Control PC Board

The Switching Control PC Board compares the shunt amp output with the current control pot setting and generates logic level PWM signals. The shunt and Shunt Amp PC Board are located between the input bridge positive and work lead to measure the output cutting current. The signals are sent to the driver PC board, where they are converted into the current and voltage levels needed to drive the switching transis- tor.

The Switching Control PC Board senses if the Remote Control (RC6010) is installed to route the current con- trol signal from the remote instead of the Merlin front panel control. The Switching Control PC Board routes the Shunt Amp signal to the remote’s current display, sends a torch voltage signal to the standoff control and supplies POT HI and POT LOW signals to set min and max output to both remote and front panel current controls. CSR (output greater than 25A) and over current shutdown (current greater than 175A) are sent to the Logic PC Board.

A relay on the Switching Control PC Board, controled by the Remote Control (RC6010) ENABLE switch or the ENABLE input on TB2, removes power from one side of the motor (MC) and main (W) contactors coils when the enable switch is off shutting off the coolant flow and DC power to allow changing torch parts.

E. Logic PC Board Functions

The Logic PC Board controls the timing and sequenc- ing of the system. It monitors the pressure, tempera- ture, and flow interlocks and controls the gas flow in

run, set, and purge modes by turning on the plasma and secondary solenoids. The Logic PC Board also controls pre-flow and post-flow durations, which are selectable by DIP switches on the board. The Logic PC Board drives the sequence status LED indicators and contains the circuit for measuring coolant con- ductivity.

After receiving the CNC (cutting machine controller) START signal from either the remote control, the standoff control, direct from the controller via the re- mote connector or TB2 the “simple” interface termi- nal strip, the Logic PC Board initiates gas preflow then energizes the main contactor, W1 or W2 (as deter- mined by the Voltage Selection PC Board).

The Logic PC Board closes the pilot contactor and sends enable signals to the Switching Control PC Board to start the PWM and turn on the main switch- ing circuits producing open circuit output voltage (OCV). When the Arc Starter Box senses OCV greater than 220 V between the Torch plus (+) and minus (-) it starts the CD (capacitor discharge) arc starting circuit to fire the spark gap producing the high voltage spark which starts the DC pilot arc. Once a constant DC pilot is established the torch voltage drops below 220 V and shuts off the CD circuit. When the Torch is close to the work the cutting arc “transfers” to the work.

The resulting current in the work lead is sensed by the Shunt Amp and the Switching Control PC Board sends the CSR signal to the Logic PC Board which opens the pilot contactor shutting off the pilot anf generating an “OK-To-Move” signal. OK-To-Move can be either contact closure or 24VAC through con- tacts selected by switch SW5 on the Logic PCB. OK- To-Move is sent to the remote control, the standoff control or directly to the cutting machine controller. It controls the optional High Flow Water Shield and the Arc Hour/Starts Counter.

F.LED/Current Control PC Board

The LED and current control PC board contains the sequence status LED indicators and the front panel current control pot.

G.Remote Control

The Remote Control allows remotely controlling the cutting current, setting reduced current for corner slowdown, and enabling gas purge and set functions. An ENABLE switch shuts down the power supply and coolant pump for changing torch consumables. The Digital Amperage display allows accurate setting and monitoring of the cutting current. Connections to the cutting machine controller (CNC) are electrically iso- lated to minimize interference. Both a rear panel con-

Manual 0-2533 17 SERVICE TROUBLESHOOTING