Reverse voltage protection for motor drive

Abstract

A reverse voltage protector for a motor drive is presented. The circuit is in series with an external electrical power source and the motor drive or electrical motor. The reverse voltage protector comprises a switch having a zener diode to protect the switch from overvoltage and a resistor regulating electrical current flow in the control terminal of the switch.

What is claimed is:  
     
         1 . A reverse voltage protector interposed between an electrical power source having a positive terminal and a negative terminal and an electrical motor, the reverse voltage protector comprising an n-channel switch having a gate terminal, a drain terminal, and a source terminal, the gate terminal connected to the positive terminal, the source terminal connected to the electrical motor, the drain terminal connected to the negative terminal, the switch remaining passively open and preventing flow of electrical power when the positive terminal and negative terminal are connected to the motor in reverse, the switch allowing flow of electrical power when the positive terminal and negative terminal are correctly connected to the motor.  
     
     
         2 . The reverse voltage protector of  claim 1  such that current flows in the switch from the source terminal to the drain terminal when the switch is on.  
     
     
         3 . The reverse voltage protector of  claim 1  further comprising: 
 a zener diode arranged in parallel with the gate terminal and the source terminal; and  
 a resistor connected to the gate terminal and the positive terminal.  
 
     
     
         4 . The reverse voltage protector of  claim 1  wherein the switch is a metal oxide semiconducter field effect transistor.  
     
     
         5 . The reverse voltage protector of  claim 1  further comprising a diode in parallel with the switch.  
     
     
         6 . A reverse voltage protector interposed between an electrical power source having a positive terminal and a negative terminal and an electrical motor, the reverse voltage protector comprising: 
 a p-channel switch having a gate terminal, a drain terminal, and a source terminal, the gate terminal connected to the negative terminal, the source terminal connected to the electrical motor, the drain terminal connected to the positive terminal, the switch remaining passively open and preventing flow of electrical power when the positive terminal and negative terminal are connected to the motor in reverse, the switch allowing flow of electrical power when the positive terminal and negative terminal are correctly connected to the motor;    
     
     
         7 . The reverse voltage protector of  claim 6  wherein the switch is a metal oxide semiconducter field effect transistor.  
     
     
         8 . The reverse voltage protector of claim further comprising: 
 a zener diode arranged in parallel with the gate terminal and the source terminal; and    a resistor connected to the gate terminal and the positive terminal.    
     
     
         9 . The reverse voltage protector of  claim 8  wherein the gate terminal has a maximum rated gate voltage and the zener diode is sized so that a maximum voltage across the gate terminal and source terminal is below the maximum rated gate voltage.  
     
     
         10 . A reverse voltage protector interposed between an electrical power source having a positive terminal and a negative terminal and an electrical motor, the reverse voltage protector comprising: 
 a switch having a control terminal, an input terminal, an output terminal, and a diode between the input terminal and the output terminal, the output terminal connected to the electrical motor, the control terminal connected to one of the positive terminal and the negative terminal and the input terminal connected to an other of the positive terminal and the negative terminal such that the switch turns on when the positive terminal and the negative terminal are correctly connected, the switch remaining passively open when the positive terminal and the negative terminal are connected to the motor in a reverse orientation.    
     
     
         11 . The reverse voltage protector of  claim 10  further comprising: 
 a zener diode arranged in parallel with the control terminal and the output terminal; and  
 a resistor connected to the control terminal and the one of the positive terminal and the negative terminal.  
 
     
     
         12 . The reverse voltage protector of  claim 10  wherein current flows through the switch in a reverse direction, the reverse direction being from the output terminal to the input terminal, the diode has a forward voltage drop, the switch has an on resistance, and the switch is selected so that the on resistance does not exceed a ratio of the forward voltage drop divided by a predetermined current magnitude flowing through the switch.  
     
     
         13 . The reverse voltage protector of  claim 12  wherein the predetermined current magnitude is a magnitude of a maximum continuous current flowing through the switch.  
     
     
         14 . The reverse voltage protector of  claim 8  wherein the control terminal has a maximum rated voltage and the zener diode is sized so that a maximum voltage across the control terminal and output terminal is below the maximum rated voltage.  
     
     
         15 . The reverse voltage protector of  claim 8  wherein the resistor has an impedance and the impedance is selected so power dissipation in the zener diode is limited to a predetermined value.