Inductance and capacitance charge pump circuit for driving power MOS transistor bridges

Abstract

The circuit comprises a tank capacitance and a charge circuit supplied with the same voltage as the bridge and comprising an inductance and a control transistor. There is also provided a control circuit, which comprises an oscillator controlling the periodic switching of control transistor and a comparator which controls the momentary clamping of control transistor in the condition wherein the charge circuit is interrupted when the difference between the voltage across capacitance and the power supply voltage exceeds a present maximum value and the unclamping of the same transistor when such difference falls below a preset minimum value. A further comparator similarly clamps control transistor if there is an excess current in the transistor itself.

What is claimed is: 
     
       1. A charge pump circuit for driving a power MOS transistor bridge where the bridge is supplied with a bridge power supply voltage, said charge pump circuit comprising: a tank capacitance for storing a charge corresponding to the driving voltage for the power MOS transistor bridge;   an inductance responsive to said bridge power supply voltage for delivering a charge current to said capacitance;   a control transistor coupled to said inductance and tank capacitance so that, in a first condition of the control transistor, the inductance delivers the charge current to the capacitance and, in a second condition thereof, the delivery of the charge current is interrupted;   an oscillator coupled to said control transistor having a preset frequency for periodically switching the control transistor between its first and second conditions; and   means including a comparator responsive to the driving voltage of the tank capacitance and the bridge power supply voltage for (a) inhibiting the periodic switching of the control transistor by the oscillator in response to the difference between the driving voltage and the bridge power supply voltage exceeding a preset maximum value and (b) restarting the said periodic switching operation in response to said difference falling below a preset minimum value.   
     
     
       2. Charge pump circuit according to claim 1 including a further comparator responsive to the magnitude of the charge current delivered by the inductance and a preset threshold for controlling the periodic switching of the control transistor by the oscillator to thus prevent excessive build up of said charging current in the inductance in response to the charging current exceeding said preset threshold. 
     
     
       3. Charge pump circuit according to claim 1, characterized in that said control transistor is of the bipolar type. 
     
     
       4. Charge pump circuit according to claim 1, characterized in that said control transistor is shunt connected between said inductance and earth with respect to said capacitance. 
     
     
       5. Charge pump circuit according to claim 1, characterized in that said comparator is of the hysteresis type. .Iadd. 
     
     
       6.  A charge pump circuit, comprising: a capacitance for storing a charge corresponding to a driving voltage;   an inductance coupled to the capacitance for delivering a charge current to the capacitance;   a control transistor coupled to the inductance and the capacitance and being responsive to a control signal having a first state causing charge current to be delivered from the inductance to the capacitance and a second state causing charge current to be stored in the inductance and not delivered to the capacitance;   an oscillator coupled to the control transistor generating a frequency for periodically supplying the first and second states of the control signal; and   a switching circuit for inhibiting the periodic supplying of the first and second states of the control signal when a difference between the driving voltage and a supply voltage exceeds a maximum value and for restarting the periodic supply of the first and second states of the control signal when the difference is less than a minimum value. .Iaddend. .Iadd.7. The charge pump circuit of claim 6, wherein the switching circuit comprises a first comparator, coupled to and responsive to the driving voltage and the supply voltage, determining a difference between the driving voltage and   
     
     
        the supply voltage. .Iaddend. .Iadd.8.  The charge pump circuit of claim 7, further comprising a second comparator, coupled to and responsive to a magnitude of the charge current and a preset threshold, controlling the periodic supplying of the first and second states of the control signal to prevent a build up of charging current in the inductance when the charging current exceeds the preset threshold. .Iaddend. .Iadd.9. The charge pump circuit of claim 6, wherein the control transistor is a bipolar transistor. .Iaddend. .Iadd.10. The charge pump circuit of claim 6, wherein the control transistor is shunt coupled between a ground and the inductance and the capacitance. .Iaddend. .Iadd.11. The charge pump circuit of claim 6, wherein the first comparator is a hysteresis type comparator. .Iaddend. .Iadd.12. The charge pump circuit of claim 7, wherein the capacitor is a tank capacitor. .Iaddend. .Iadd.13. The charge pump of claim 7, wherein the supply voltage is provided by a bridge power supply. .Iaddend. .Iadd.14. The charge pump circuit of claim 13, wherein the charge pump circuit supplies the driving voltage to a power MOS 
     
     
        transistor bridge. .Iaddend. .Iadd.15.  A charge pump circuit, comprising: a capacitance means for storing a charge corresponding to a driving voltage;   an inductance means coupled to the capacitance means for delivering a charge current to the capacitance means;   a control transistor means, coupled to the capacitance means and the inductance means, and having means for responding to a control signal having a first state causing charge current to be delivered from the inductance means to the capacitance means and a second state causing charge current to be stored in the inductance means and not delivered to the capacitance means;   an oscillator means, coupled to the control transistor means, for generating a frequency for periodically supplying the first and second states of the control signal; and   a switching circuit means for inhibiting the periodic supplying of the first and second states of the control signal when a difference between the driving voltage and a supply voltage exceeds a maximum value and for restarting the periodic supplying of the first and second states of the control signal when the difference is less than a minimum value. .Iaddend.   
     
     
        .Iadd.16.  The charge pump circuit of claim 15, wherein the switching circuit means comprises a first comparator means, coupled to and responsive to the driving voltage and the supply voltage, for determining a difference between the driving voltage and the supply voltage. .Iaddend. .Iadd.17. The charge pump circuit of claim 16, further comprising a second comparator means, coupled to and responsive to a magnitude of the charge current and a preset threshold, for controlling the periodic supplying of the first and second states of the control signal to prevent a build up of charging current in the inductance means when the charging current exceeds the preset threshold. .Iaddend. .Iadd.18. The charge pump circuit of claim 17, wherein the first comparator means is a hysteresis type comparator means. .Iaddend. .Iadd.19. The charge pump circuit of claim 18, wherein the control transistor means is shunt coupled between a ground and the inductance means and the capacitance means. .Iaddend. .Iadd.20. The charge pump circuit of claim 19, wherein the capacitance means is a tank capacitor. .Iaddend.