A surge protection circuit

A surge protection circuit for use between a DC power supply and a load, the surge protection circuit comprising:

• a positive power terminal, of the surge protection circuit, configured to connect between a positive output of the DC power supply and a positive input of the load, and
• a negative power terminal, of the surge protection circuit, configured to connect between a negative output of the DC power supply and a negative input of the load;
• a protective earth terminal configured to connect to a protective earth;
• a voltage clamping circuit connected between the one of the positive and negative power terminals and the protective earth terminal and adapted to:
• reduce its impedance to a low impedance and clamp the voltage across the voltage clamping circuit, responsive to a surge voltage between the one of the positive and negative power terminals and the protective earth terminal across the voltage clamping circuit exceeding a surge threshold voltage;
• and
• recover to a high impedance responsive to an electrical parameter across the voltage clamping circuit falling below a recovery threshold;
• and
• a control circuit, comprising
• a detecting component configured to sense a current through the voltage clamping circuit to the protective earth;
• and
• an active switch connected between the positive power terminal;
• wherein the control circuit is adapted to operate the active switch, responsive to the sensed current, to short circuit the DC power supply after the surge voltage ends, to limit the electrical parameter across the voltage clamping circuit below the recovery threshold to thereby cause the voltage clamping circuit to recover to the high impedance,
• a recoverable component connected in series with the voltage clamping circuit;
• and
• an active switch is connected in parallel with said recoverable component, wherein recoverable component has a smaller voltage rating than that of the voltage clamping circuit and the control circuit is configured to operate the active switch to cause the voltage clamping circuit to recover to the high impedance by closing the active switch to bypass the recoverable component and recover the recoverable component to a high impedance state;
• and subsequently opening the active switch to thereby cut off current through the voltage clamping circuit.