Intrinsically safe energy limiting circuit

1. An intrinsically safe energy limiting circuit for connection between an upstream DC power source and a downstream electrical load powered from the upstream DC power source, said energy limiting circuit from upstream to downstream comprising:

an input for connection to the upstream DC power source;

an electronic current limiter configured to limit a current through the energy limiting circuit to a maximum value if the current reaches the maximum value;

a fuse designed to open at a current value greater than said maximum value;

a switch-mode DC-to-DC converter configured to convert a DC input voltage to a lower nominal DC output voltage;

a zener barrier having a zener voltage higher than the DC output voltage; and

an output for connected to the downstream electrical load.

2. The energy limiting circuit of claim 1 , further comprising for each of at least one further electrical load to be powered:

a further switch-mode DC-to-DC converter downstream connected to said fuse and configured to convert the DC input voltage to a further lower DC output voltage;

a further zener barrier having a zener voltage higher than the further DC output voltage; and

a further output for connection to the further electrical load.

3. The energy limiting circuit of claim 1 , wherein the electronic current limiter comprises a current sensor, a semiconductor series pass element in series with the current sensor, and a control circuit including an operational amplifier and being responsive to the current sensor for providing a control signal to the semiconductor series pass element which limits the current through the energy limiting circuit.

4. The energy limiting circuit of claim 2 , wherein the electronic current limiter comprises a current sensor, a semiconductor series pass element in series with the current sensor, and a control circuit including an operational amplifier and being responsive to the current sensor for providing a control signal to the semiconductor series pass element which limits the current through the energy limiting circuit.

5. The energy limiting circuit of claim 3 , wherein the electronic current limiter further comprises an overvoltage sensor; and wherein the control circuit is further responsive to the overvoltage sensor to provide the control signal to the semiconductor series pass element.

6. The energy limiting circuit of claim 3 , wherein the electronic current limiter further comprises an undervoltage sensor; and wherein the control circuit is further responsive to the undervoltage sensor to provide the control signal to the semiconductor series pass element.

7. The energy limiting circuit of claim 5 , wherein the electronic current limiter further comprises an undervoltage sensor; and wherein the control circuit is further responsive to the undervoltage sensor to provide the control signal to the semiconductor series pass element.

8. The energy limiting circuit of claim 3 , wherein the electronic current limiter further comprises a turn-on delay circuit; and wherein the control circuit is further responsive to the turn-on delay circuit to provide the control signal to the semiconductor series pass element.

9. The energy limiting circuit of claim 5 , wherein the electronic current limiter further comprises a turn-on delay circuit; and wherein the control circuit is further responsive to the turn-on delay circuit to provide the control signal to the semiconductor series pass element.

10. The energy limiting circuit of claim 6 , wherein the electronic current limiter further comprises a turn-on delay circuit; and wherein the control circuit is further responsive to the turn-on delay circuit to provide the control signal to the semiconductor series pass element.