Circuit for protecting against reverse polarity

A circuit for the protection of an electrical consumer against polarity reversal, said circuit comprising:

• a metal oxide semiconductor field effect transistor (MOSFET) (T1);
• a first diode;
• a second diode;
• and
• a resistor (R4) arranged between the first diode and a drain of the MOSFET (T1),
• wherein:
• the circuit is connected to a voltage supply on its input, and to the consumer on its output;
• the source terminal of the MOSFET (T1) is connected to the voltage supply;
• the drain terminal of the MOSFET (T1) is connected to the consumer;
• the gate of the MOSFET (T1) is connected to the collector of a first bipolar transistor (T3);
• the source of the MOSFET (T1) is connected to the emitter of the first bipolar transistor (T3);
• the base of the first bipolar transistor (T3) is controlled by means of a control current;
• the control current is derived from the voltage at the drain of the MOSFET (T1);
• the first diode is configured for tapping the control current from the voltage of the drain of the MOSFET (T1);
• the resistor (R4) is configured to control the voltage drop across the MOSFET (T1);
• and
• the MOSFET (T1) is an n-channel enhancement MOSFET;
• the first diode is formed by the base-emitter path of a second bipolar transistor (T2);
• the second diode is arranged between the emitter and the base of the second bipolar transistor (T2);
• and
• the second diode being configured to prevent an excessively high voltage flowing backward between the emitter and the base in the event of a reversal in polarity or of an interruption in the supply voltage.