Power supply connected in parallel with solid state switch for phase control of average power to a load

• US 5,550,463 A
• Filed: 12/15/1994
• Issued: 08/27/1996
• Est. Priority Date: 05/20/1993
• Status: Expired due to Fees

• Current Assignee: Michael Coveley
• Original Assignee: Michael Coveley
• Inventors: Coveley, Michael
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/356,501
• Time in Patent Office: 621 Days
• Field of Search: 323/237, 323/239, 323/300, 323/320, 323/325, 315/194
• US Class Current: 323/300
• CPC Class Codes: G05F 1/56 using semiconductor devices in series with the load as final control devices G05F1/461 takes precedence
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 5/2573 with control circuit

Abstract

A power supply for controlling average power to a load, such as an electric light, heater or motor, comprising a solid state switch connected in series with the load, a power supply connected in parallel with the solid state switch, and a control circuit connected intermediate the power supply and solid state switch for causing the solid state switch to conduct current through the load for a predetermined portion of each AC power cycle. The power supply collects charge whenever the solid state switch is non-conducting. According to the preferred embodiment, a current overload detector and zero crossing detector are also provided for increased reliability and precise definition of the solid state switch conduction timing.

Claims

1. A circuit for controlling average power applied to a load from a source of alternating supply voltage, comprising:

(a) a solid state switch connected in series with said load across said source of alternating supply voltage;

(b) a zero crossing detector connected in parallel with said solid state switch for receiving said alternating supply voltage and in response generating an output signal indicative of each zero crossing of said alternating supply voltage, said zero crossing detector including a positive feedback loop to maintain generally the magnitude of said output signal for its duration;

(c) a control circuit connected in parallel with said solid state switch for receiving said output signal from said zero crossing detector and in response generating and applying a gating signal to said solid state switch whereby said solid state switch is caused to conduct current after a predetermined delay time following each said zero crossing of said alternating supply voltage; and

(d) a power supply connected in parallel with said solid state switch for receiving charging current from said source of alternating supply voltage when said solid state switch is not conducting current, and in response generating a regulated DC output voltage for application to said control circuit and said zero crossing detector.

2. The circuit of claim 1, further comprising a current overload detector connected in series with said load and said solid state switch for detecting current flowing through said load in excess of a predetermined amount and in response generating a signal for disabling said control circuit and thereby disabling said solid state switch.

3. The circuit of claim 2, wherein said current overload detector includes a resistor connected to said solid state switch and transistor means having a control input connected to said resistor and a signal output connected to said control circuit, said transistor means being enabled in response to a voltage drop across said resistor in excess of a predetermined voltage corresponding to said predetermined amount of current flowing through said load.

4. The circuit of claim 1, wherein said solid state switch is a triac having a first signal terminal connected to said load, a gate terminal connected to said control circuit, and a second signal terminal connected to said source of alternating supply voltage.

5. A circuit for controlling average power applied to a load from a source of alternating supply voltage, comprising:

(a) a solid state switch connected in series with said load across said source of alternating supply voltage;

(b) a zero crossing detector connected in parallel with said solid state switch for receiving said alternating supply voltage and in response generating an output signal indicative of each zero crossing of said alternating supply voltage;

(c) a control circuit connected in parallel with said solid state switch for receiving said output signal from said zero crossing detector and in response generating and applying a gating signal to said solid state switch whereby said solid state switch is caused to conduct current after a predetermined delay time following each said zero crossing of said alternating supply voltage; and

(d) a power supply connected in parallel with said solid state switch for receiving charging current from said source of alternating supply voltage when said solid state switch is not conducting current, and in response generating a regulated DC output voltage for application to said control circuit and said zero crossing detector, wherein said zero crossing detector includes;

transistor means having a control input connected to a first terminal of said solid state switch, a signal input for receiving said regulated DC output voltage, and a signal output;

first diode means having an anode connected to said signal output and a cathode connected to said control input;

second diode having an anode connected to a second terminal of said solid state switch and a cathode connected to the anode of said first diode means and said signal output of said transistor means;

operational amplifier means having a first input connected to said signal output of said transistor means, a second input for receiving a source of threshold voltage, and an output connected in a positive feedback path to said first input, for generating a first polarity output signal responsive to a positive going zero crossing of said alternating supply voltage and an opposite polarity output signal responsive to a negative going zero crossing of said alternating supply voltage.

6. The circuit of claim 5, further comprising a current overload detector connected in series with said load and said solid state switch for detecting current flowing through said load in excess of a predetermined amount and in response generating a signal for disabling said control circuit and thereby disabling said solid state switch.

7. The circuit of claim 6, wherein said current overload detector includes a resistor connected to said solid state switch and transistor means having a control input connected to said resistor and a signal output connected to said control circuit, said transistor means being enabled in response to a voltage drop across said resistor in excess of a predetermined voltage corresponding to said predetermined amount of current flowing through said load.

8. The circuit of claim 7, wherein said solid state switch is a triac having a first signal terminal connected to said load, a gate terminal connected to said control circuit, and a second signal terminal connected to said source of alternating supply voltage.

10. The circuit of claim 6, further comprising a current overload detector connected in series with said load and said solid state switch for detecting current flowing through said load in excess of a predetermined amount and in response generating a signal for disabling said control circuit and thereby disabling said solid state switch.

11. The circuit of claim 10, wherein said current overload detector includes a resistor connected to said solid state switch and transistor means having a control input connected to said resistor and a signal output connected to said control circuit, said transistor means being enabled in response to a voltage drop across said resistor in excess of a predetermined voltage corresponding to said predetermined amount of current flowing through said load.

14. The circuit of claim 7, further comprising a current overload detector connected in series with said load and said solid state switch for detecting current flowing through said load in excess of a predetermined amount and in response generating a signal for disabling said control circuit and thereby disabling said solid state switch.

15. The circuit of claim 14, wherein said current overload detector includes a resistor connected to said solid state switch and transistor means having a control input connected to said resistor and a signal output connected to said control circuit, said transistor means being enabled in response to a voltage drop across said resistor in excess of a predetermined voltage corresponding to said predetermined amount of current flowing through said load.

16. The circuit of claim 15, wherein said solid state switch is a triac having a first signal terminal connected to said load, a gate terminal connected to said control circuit, and a second signal terminal connected to said source of alternating supply voltage.

9. A circuit for controlling average power applied to a load from a source of alternating supply voltage, comprising:

(a) a solid state switch connected in series with said load across said source of alternating supply voltage;

(b) a zero crossing detector connected in parallel with said solid state switch for receiving said alternating supply voltage and in response generating an output signal indicative of each zero crossing of said alternating supply voltage;

(c) a control circuit connected in parallel with said solid state switch for receiving said output signal from said zero crossing detector and in response generating and applying a gating signal to said solid state switch whereby said solid state switch is caused to conduct current after a predetermined delay time following each said zero crossing of said alternating supply voltage; and

(d) a power supply connected in parallel with said solid state switch for receiving charging current from said source of alternating supply voltage when said solid state switch is not conducting current, and in response generating a regulated DC output voltage for application to said control circuit and said zero crossing detector, wherein said power supply includes;

a first capacitor having first and second terminals, said first terminal of said first capacitor being connected to a first signal terminal of said solid state switch;

a resistor having first and second terminals, said first terminal of said resistor being connected to said second terminal of said first capacitor;

a Zener diode having a cathode connected to an opposite signal terminal of said solid state switch and an anode connected to said second terminal of said resistor;

a further diode having an anode and cathode, said anode being connected to said second terminal of said resistor;

a second capacitor having a first terminal connected to said cathode of said further diode and a second terminal connected to said opposite signal terminal of said solid state switch, said second capacitor operating as a charge reservoir;

a voltage regulator having a first input connected to said first terminal of said second capacitor, a second input connected to said opposite signal terminal of said solid state switch, and an output terminal, for generating said regulated DC output voltage in response to charge accumulated in said second capacitor; and

a filtering output capacitor connected to said output terminal of said voltage regulator and said opposite signal terminal of said solid state switch.

12. A circuit for controlling average power applied to a load from a source of alternating supply voltage, comprising:

(a) a solid state switch connected in series with said load across said source of alternating supply voltage;

(b) a zero crossing detector connected in parallel with said solid state switch for receiving said alternating supply voltage and in response generating an output signal indicative of each zero crossing of said alternating supply voltage;

(c) a control circuit connected in parallel with said solid state switch for receiving said output signal from said zero crossing detector and in response generating and applying a gating signal to said solid state switch whereby said solid state switch is caused to conduct current after a predetermined delay time following each said zero crossing of said alternating supply voltage; and

(d) a power supply connected in parallel with said solid state switch for receiving charging current from said source of alternating supply voltage when said solid state switch is not conducting current, and in response generating a regulated DC output voltage for application to said control circuit and said zero crossing detector wherein said power supply includes;

a diode having a cathode and anode, said anode being connected to a first signal terminal of said solid state switch;

a first resistor having first and second terminals, said first terminal of said resistor being connected to said cathode of said diode;

a Zener diode having a cathode connected to an opposite signal terminal of said solid state switch and an anode connected to said second terminal of said first resistor;

a further diode having an anode and cathode, said anode being connected to said second terminal of said first resistor;

a second resistor having first and second terminals, said first terminal being connected to the first terminal of said first resistor;

a transistor having first and second signal terminals and a control terminal, said first signal being connected to the second terminal of said second resistor and said control terminal being connected to the cathode of said Zener diode;

a first capacitor having a first terminal connected to the second signal terminal of said transistor and a second terminal connected to said opposite signal terminal of said solid state switch;

a second capacitor having a first terminal connected to the second signal terminal of said transistor and a second terminal connected to said opposite signal terminal of said solid state switch, said second capacitor operating as a charge reservoir;

a voltage regulator having a first input connected to said first terminals of said first and second capacitors, a second input connected to said opposite signal terminal of said solid state switch, and an output terminal, for generating said regulated DC output voltage in response to charge accumulated in said second capacitor; and

a filtering output capacitor connected to said output terminal of said voltage regulator and said opposite signal terminal of said solid state switch.

13. The circuit of claim 12, wherein said solid state switch is a triac having a first signal terminal connected to said load, a gate terminal connected to said control circuit, and a second signal terminal connected to said source of alternating supply voltage.

17. A circuit for controlling average power applied to a load from a source of alternating supply voltage, comprising:

(a) a solid state switch connected in series with said load across said source of alternating supply voltage;

(b) a zero crossing detector connected in parallel with said solid state switch for receiving said alternating supply voltage and in response generating an output signal indicative of each zero crossing of said alternating supply voltage;

(c) a control circuit connected in parallel with said solid state switch for receiving said output signal from said zero crossing detector and in response generating and applying a gating signal to said switch whereby said solid state switch is caused to conduct current after a predetermined delay time following each said zero crossing of said alternating supply voltage;

(d) a power supply connected in parallel with said solid state switch for receiving charging current from said source of alternating supply voltage when said solid state switch is not conducting current, and in response generating a regulated DC output voltage for application to said control circuit and said zero crossing detector; and

(e) a current overload detector connected in series with said load and said solid state switch for detecting current flowing through said load in excess of a predetermined amount and in response generating a signal for disabling said control circuit and thereby disabling said solid state switch, said current overload detector including a resistor connected to said solid state switch and transistor means having a control input connected to said resistor and a signal output connected to said control circuit, said transistor means being enabled in response to a voltage drop across said resistor in excess of a predetermined voltage corresponding to said predetermined amount of current flowing through said load.

18. The circuit of claim 17, wherein said solid state switch is a triac having a first signal terminal connected to said load, a gate terminal connected to said control circuit, and a second signal terminal connected to said source of alternating supply voltage.