Next: Authorization, Copyright and legal Up: How Pierre Curie protects Previous: Protection of the galvanic

More measures designed to protect the insulation barrier

In the circuit (Fig. 4) it has been taken into account that not only the insulation of the transformer, but also the optocoupler required for control purposes must be protected from melting. In most cases it is of course usual that bonding wires act as fuses and blow if high voltages are applied to the transistor of the optocoupler, however, this is not safe and is therefore not allowed for safety reasons. The high-impedance resistance R2 with a load capacity of 1 Watt limits the current flowing through the collector circuit of the optocoupler in such a way that the development of heat inside the optocoupler is ruled out and the 2 mm thick plastic insulation of the optocoupler can be melted.

For the fuse F1 (125 mA, TR5) with its limited current breaking capacity of 35 A to blow even when the industrial power system is able to supply a current of 1500 A (according to the failure assumptions described in the regulations), a low-impedance resistor R1 will be preconnected that is able to keep the current below 35 A at 250 Vrms until the fuse blows without arcing or exploding.

All these measures aim to prevent the energy out of the mains from getting to the output side (explosion-proof and intrinsically safe circuit), regardless of whether the power supply is still working at the time or not.

Next: Authorization, Copyright and legal Up: How Pierre Curie protects Previous: Protection of the galvanic