Method and circuit for controlling current in an inductive load

• US 6,294,905 B1
• Filed: 05/02/2000
• Issued: 09/25/2001
• Est. Priority Date: 05/03/1999
• Status: Expired due to Term

• Current Assignee: STMicroelectronics GmbH (STMicroelectronics NV)
• Original Assignee: STMicroelectronics GmbH (STMicroelectronics NV)
• Inventors: Schwartz, Reiner
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US09/565,356
• Time in Patent Office: 511 Days
• Field of Search: 323/288, 323/284, 323/283, 323/282
• US Class Current: 323/288
• CPC Class Codes: H01H 47/325 by switching regulator
• CPC Class Codes: H03K 17/64 having inductive loads

Abstract

A control or adjusting circuit for a load, a desired signal is compared to an actual signal corresponding to the state of the load, and a PWM control signal is generated in a control signal generating circuit in accordance with the comparison result. The control signal opens and closes a current switch coupled to the load. For forming the PWM control signal, the contents of a ramp counter are compared to the contents of an up/down counter by means of a digital comparator. To obtain fast approximation of the two signals to each other in the case of strong deviations between the desired signal and the actual signal, the up/down counter is subjected to relatively rapid counting in case of high control deviations as compared to low control deviations. To this end, the up/down counter is operated with a clock signal of variable frequency that is produced by a voltage-controlled oscillator as a function of the difference between the desired signal and the actual signal.

Claims

1. An electric circuit for controlling a load in accordance with a desired signal, said circuit comprising:

a first signal source issuing the desired signal;

a second signal source issuing an actual signal representative of the current state of the load;

a controller coupled to the load and having a control terminal; and

a control signal generating circuit which at an input thereof receives a deviation signal representative of the difference between the desired signal and the actual signal, which generates a PWM control signal in accordance with the deviation signal and which feeds the control signal via an output to the control terminal of the controller, the control signal generating circuit including a counter operated in accordance with the deviation signal so as to generate the PWM control signal, and a count clock input of the counter being connected to the output of a voltage-controlled oscillator receiving the deviation signal at the input thereof.

2. The circuit of claim 1,

further comprising a comparator circuit configured to compare the desired signal to the actual signal and to generate the deviation signal at the output thereof.

3. The circuit of claim 1,

wherein a digital comparator is provided having a first and a second input and an output, the first input connected to the output of the counter, the second input connected to a reference value generator, and the output connected to the control input of the controller.

4. The circuit of claim 1,

wherein a pulse shaper is connected between the voltage-controlled oscillator and the count clock input of the counter.

5. The circuit of claim 3,

wherein a monoflop is connected between the output of the digital comparator and the control terminal of the switching element, and wherein the output of the digital comparator or of the monoflop is connected to a resetting input of the counter.

12. The circuit of claim 1, further comprising a comparator circuit configured to compare the desired signal to the actual signal and to generate the deviation signal at the output thereof.

13. The circuit of claim 12, wherein a digital comparator is provided having a first and a second input and an output, the first input connected to the output of the counter, the second input connected to a reference value generator, and the output connected to the control input of the controller.

6. A digital integrator for integrating an analog signal, comprising:

an input fed with the analog signal;

a sign generator receiving the analog signal and generating a sign signal;

a voltage-controlled oscillator receiving the analog signal and generating an oscillation signal the frequency of which is dependant on the amplitude of the analog signal; and

an up/down counter receiving the sign signal and the oscillation signal of the voltage-controlled oscillator and issuing an up-counting or down-counting digital signal at the output thereof in accordance with the sign signal and that is representative of an integration of the analog signal.

7. A method for controlling current in an inductive load, comprising:

generating an actual current signal corresponding to the state of the current in the inductive load;

comparing the actual current signal to a reference signal and generating a comparison signal;

generating a PWM control signal to a control switch coupled to the inductive load using a counter that is responsive to the comparison signal to control the current in the inductive load.

8. The method of claim 7 wherein generating the control signal comprises:

receiving the comparison signal;

generating a counter signal of variable speed in response to the comparison signal and generating a ramp counter signal in response to a fixed clock signal, the direction of the counter signal dependent on the sign of the comparison signal; and

comparing the counter signal to the ramp counter signal and generating a PWM signal as the control signal.

9. The method of claim 8 comprising increasing the speed of the counter signal as the difference between the actual current signal and the reference signal increases.

10. The method of claim 8 wherein generating a variable-speed counter signal comprises generating a clock signal of variable frequency produced by a voltage-controlled oscillator as a function of the difference between the actual current signal and the reference signal, and clocking an up/down counter with the variable-frequency clock signal to output the variable-speed counter signal.

11. A circuit for controlling current in an inductive load in accordance with a desired signal, the circuit comprising:

a first signal source issuing the desired signal;

a second signal source issuing an actual signal representative of the current state of the inductive load;

a controller coupled to the inductive load and having a control terminal; and

a control signal generating circuit having an input configured to receive a deviation signal representative of the difference between the desired signal and the actual signal, the control signal generating circuit configured to generate a PWM control signal in accordance with the deviation signal and that feeds the control signal via an output of the control terminal of the controller, the control signal generating circuit including an up/down counter operated in accordance with the deviation signal to generate the PWM control signal, a count clock input of the counter being connected to the output of a voltage-controlled oscillator receiving the deviation signal at the input thereof, the up/down counter configured to generate the PWM control signal in an up-direction or a down-direction, respectively, as determined by the sign of the deviation signal.

14. The circuit of claim 11, wherein a pulse shaper is connected between the voltage-controlled oscillator and the clock count input of the counter.

15. The circuit of claim 14, wherein a monoflop is connected between the output of the digital comparator and the control terminal of the switching element, and wherein the output of the digital comparator or of the monoflop is connected to a resetting input of the counter.

16. A circuit for controlling current in an inductive load in accordance with a desired signal, the circuit comprising:

a first signal source issuing the desired signal;

a second signal source issuing an actual signal representative of the current state of the load;

a controller coupled to the load and having a control terminal;

a control signal generating circuit having an input configured to receive a deviation signal representative of the difference between the desired signal and the actual signal, the control signal generating circuit configured to generate a PWM control signal in accordance with the deviation signal and which feeds the control signal via an output to the control terminal of the controller, the control signal generating circuit including a counter operated in accordance with the deviation signal so as to generate the PWM control signal, and a count clock input of the counter connected to the output of a voltage-controlled oscillator receiving the deviation signal at the input thereof; and

a digital comparator having a first and a second input and an output, the first input connected to the output of the counter, the second input connected to a reference value generator, and the output connected to the control input of the controller, the reference value generator comprising a ramp counter.

17. The circuit of claim 16, further comprising a pulse shaper connected between the voltage-controlled oscillator and the clock input of the counter.

18. The circuit of claim 17, wherein a monoflop is connected between the output of the digital comparator and the control terminal of the switching element, and wherein the output of the digital comparator or of the monoflop is connected to a resetting input of the counter.