3.2   Rectifier, Inrush-Current-Limiter + Filter

3.2.1   Current Limiter

When switching the power supply on, the smoothing Capacitor will be charged. Initially it acts like a short circuit and without current-limiting the fuses would be blown. This effect may also occur, if the voltage supply is interrupted for a short time (t_interrupt > 0.3s). In both cases, a current-limiting resistor must be switched in series between the fuses and the capacitors.

The current-limiting and supply-voltage-interruption-detection circuit was simulated with Microsim PSpice. The current-limiter is implemented on the Rectifier + Inrush current limiter PCB, the supply-voltage-interrupting detector on the Protection-PCB (Figure 3.5).

Figure 3.3 shows the schematics of the PSpice - simulation. C1 is the smoothing capacitor. Switch_1 and Switch_2 simulate two seconds of interruption of the power-supply. When the circuit is connected to the power supply, the capacitors C_div_1, C_div_2 and C_div_3 are charged and the output-signal of IC4B is low. For the first 1.5s the IGBT is nonconductive and C1 is charged over R_culi_4. Then the voltage-level at the IGBT-gate reaches about 5V, the IGBT starts to conduct and after 4.5s the gate-voltage reaches 15V.

Figure 3.2 shows the simulation data in the case of a one-phase interruption for two seconds.

Figure 3.2: Supply Voltage Interruption Detector: Simulation Data 0-10s

Figure 3.3: PSpice schematics: Supply voltage interruption detector and current limiter

Figure 3.4 is a magnification of the timeframe at the moment when one phase is switched off (at 5s). IC3A detects the interruption after 60ms (curve: IC3A:Y) and the gate-voltage of the IGBT (upper curve) decreases. The 5V-limit (where the status of the IGBT changes to non-conducting) is reached 0.2s after the interruption.

Figure 3.4: Supply Voltage Interruption Detector: Simulation Data 4.8-5.5s

Figure 3.5 shows the Protel schematic for the layout of the protection board. The upper circuit is the logic for the overheat protection. The signals come from the temperature sensors (paragraph 3.7), connected to J_in_high_temp. The circuit in the middle is to control the fan. Connector J_in_low_temp is connected to the temperature sensors. At J_out_fan, a 230V~ fan is connected. The lower circuit is the implementation of the voltage gap detection and the 5V power supply for the logic circuits on the protection board, the temperature sensors, the control board and the digital signal generator.

Figure 3.55: Protel Schematic: Protection Board

This page is part of a Frameset: Electrodynamic Sculpture: A Thesis by Rafael Bräg.