Claims
- 1. A circuit for controlling the RMS value of an AC voltage applied to a partially resistive and partially inductive load comprising:
- (a) only a pair of wires for connection in series with the load and an AC supply voltage;
- (b) first bidirectional electronic switch means operatively coupled across the pair of wires and having control input means for selectively rendering the first electronic switch means conductive to apply AC voltage to the load, the first electronic switch means having first and second thyristors, each having a gate terminal and first and second main terminals, the first main terminal of the first thyristor being operatively coupled to one of the pair of wires, a first resistor operatively coupling the second main terminal of the first thyristor to the other one of the pair of wires, the main terminals of the second thyristor operatively coupled directly across the pair of wires, the gate terminal of the first thyristor receiving control signals from the control circuit, the gate terminal of the second thyristor being operatively coupled to a junction between the first resistor and the second main terminal of the first thyristor, the first and second thyristors each having a holding current characteristic, the holding current characteristic of the first thyristor being substantially less than the holding characteristic of the second thyristor,
- (c) a control circuit operatively coupled to the control input means and responsive to the instantaneous magnitude of the AC voltage appearing across the pair of wires for repetitively rendering the first electronic switch means conductive at selected periods of time defining a firing angle; and
- (d) voltage compensating means in series with correction means operatively coupled across the pair of wires for regulating the RMS value of the AC voltage applied to the load and for correcting asymmetries in the waveform of the AC voltage applied to the load.
- 2. Circuit according to claim 1 wherein the voltage compensating means comprises second, voltage sensitive, bidirectional electronic switch means having a breakover voltage that is applied to the control circuit during periods of conduction of the second electronic switch means, the control circuit being responsive to the breakover voltage and to fluctuations in the AC supply voltage to adjust the firing angle and thereby regulate the RMS value of the AC voltage applied to the load.
- 3. Circuit according to claim 2 wherein the first electronic switch means comprises thyristor means and the second electronic switch means comprises diac means.
- 4. Circuit according to claim 1 wherein the correction means comprises a capacitor operatively coupled to the control circuit for adjusting the firing angle of the first electronic switch means during succeeding half cycles of the waveform of the AC voltage applied to the load.
- 5. Circuit according to claim 1 wherein the first and second thyristors each have a maximum current rating, the maximum current rating of the first thyristor being less than approximately 1/10 the maximum current rating of the second thyristor.
- 6. Circuit according to claim 1 wherein the first thyristor has a maximum current rating and the value of the first resistor is such that there is approximately one volt across the first resistor when the current therethrough is from about 1/10 to 1/2 the maximum current rating.
- 7. Circuit according to claim 1 wherein the control circuit comprises adjustably controllable means for manually adjusting the firing angle to alter the RMS value of the AC voltage applied to the load.
- 8. Circuit according to claim 7 wherein the adjustably controllable means comprises a potentiometer and the control circuit further comprises a first diac in series circuit connection between a first terminal of potentiometer and the gate terminal of the first thyristor, and a first capacitor operatively coupled between (i) the junction of the first diac and the first terminal of the potentiometer and (ii) one of the pair of wires.
- 9. Circuit according to claim 8 wherein the voltage compensating means comprises a second diac having a first terminal operatively coupled to a second terminal of the potentiometer and having a breakover voltage when in conduction, the breakover voltage being applied to the potentiometer during periods of conduction, the control circuit being responsive to the breakover voltage and to fluctuations in the AC supply voltage to adjust the firing angle and thereby regulate the RMS value of the AC voltage applied to the load at a value indicated by the setting of potentiometer.
- 10. Circuit according to claim 9 wherein the correction means comprises a second capacitor operatively coupled between a second terminal of the second diac and one of the pair of wires.
- 11. Circuit according to claim 10 further comprising a second resistor operatively coupled between (i) the junction of the second capacitor and the second terminal of the second diac and (ii) one of the pair of wires for charging the second capacitor to a voltage indicative of the magnitude and polarity of a DC current flowing through the load, the second capacitor voltage effectively adjusting the breakover voltage of the second diac and thereby altering the firing angle in selected half cycles of the waveform of the AC voltage applied to the load to decrease the DC current flowing through the load.
- 12. Circuit according to claim 9 further comprising a series combination of a second resistor and a second capacitor operatively coupled across the pair of wires, a feedback loop from the junction of the second capacitor and second resistor to the junction of the first capacitor and the first diac, the second capacitor charging to a voltage indicative of the magnitude and polarity of a DC current flowing through the load, the second capacitor voltage altering the voltage normally applied to the first diac by the first capacitor and thereby altering the firing angle in selected half cycles of the waveform of the AC voltage applied to the load to decrease the DC current flowing through the load.
- 13. Circuit according to claim 1 wherein the load is a low voltage transformer.
- 14. Circuit according to claim 1 wherein the load is a ballast.
- 15. Circuit according to claim 3 wherein the thyristor means comprises triac means.
- 16. Circuit according to claims 1, 5, 6, 7, 8, 9, 10, 11 or 12 wherein the first and second thyristors comprise first and second triacs, respectively.
- 17. A circuit for controlling the RMS value of an AC voltage applied to a partially resistive and partially inductive load comprising:
- (a) only a pair of wires for connection in series with the load and an AC supply voltage;
- (b) first bidirectional electronic switch means operatively coupled across the pair of wires and having control input means for selectively rendering the first electronic switch means conductive to apply AC voltage to the load, the first electronic switch means having first and second thyristors, each having a gate terminal and first and second main terminals, the first main terminal of the first thyristor being operatively coupled to one of the pair of wires, a first resistor operatively coupling the second main terminal of the first thyristor to the other one of the pair of wires, the main terminals of the second thyristor operatively coupled directly across the pair of wires, the gate terminal of the first thyristor receiving control signals from the control circuit, the gate terminal of the second thyristor being operatively coupled to a junction between the first resistor and the second main terminal of the first thyristor, the first and second thyristors each having a holding current characteristic, the holding current characteristic of the first thyristor being substantially less than the holding characteristic of the second thyristor,
- (c) a control circuit operatively coupled to the control input means and responsive to the instantaneous magnitude of the AC voltage appearing across the pair of wires for repetitively rendering the first electronic switch means conductive at selected periods of time defining a firing angle, the control circuit including adjustably controllable means for manually adjusting the firing angle to alter the RMS value of the AC voltage applied to the load and a first diac in series circuit connection between a first terminal of potentiometer and the gate terminal of the first thyristor, and a first capacitor operatively coupled between (i) the junction of the first diac and the first terminal of the potentiometer and (ii) one of the pair of wires;
- (d) voltage compensating means operatively coupled across the pair of wires for regulating the RMS value of the AC voltage applied to the load, the voltage compensating means including a second diac having a first terminal operatively coupled to a second terminal of the potentiometer and having a breakover voltage when in conduction, the breakover voltage being applied to the potentiometer during periods of conduction, the control circuit being responsive to the breakover voltage and to fluctuations in the AC supply voltage to adjust the firing angle and thereby regulate the RMS value of the AC voltage applied to the load at a value indicated by the setting of potentiometer; and
- (e) correction means operatively coupled across the first electronic switch means for correcting asymmetries in the waveform of the AC voltage applied to the load, the correction means including a second capacitor operatively coupled between a second terminal of the second diac and one of the pair of wires.
- 18. Circuit according to claim 17 further comprising a second resistor operatively coupled between (i) the junction of the second capacitor and the second terminal of the second diac and (ii) one of the pair of wires for charging the second capacitor to a voltage indicative of the magnitude and polarity of a DC current flowing through the load, the second capacitor voltage effectively adjusting the breakover voltage of the second diac and thereby altering the firing angle in selected half cycles of the waveform of the AC voltage applied to the load to decrease the DC current flowing through the load.
- 19. Circuit according to claim 17 further comprising a series combination of a second resistor and a second capacitor operatively coupled across the pair of wires, a feedback loop from the junction of the second capacitor and second resistor to the junction of the first capacitor and the first diac, the second capacitor charging to a voltage indicative of the magnitude and polarity of a DC current flowing through the load, the second capacitor voltage altering the voltage normally applied to the first diac by the first capacitor and thereby altering the firing angle in selected half cycles of the waveform of the AC voltage applied to the load to decrease the DC current flowing through the load.
- 20. Circuit according to claim 17, 18 or 19 wherein the first and second thyristors comprise first and second triacs, respectively.
Parent Case Info
This a continuation of co-pending application Ser. No. 839,304 filed on Mar. 13, 1986.
US Referenced Citations (8)
Foreign Referenced Citations (7)
Number |
Date |
Country |
2550027 |
Feb 1985 |
FRX |
95125 |
Jul 1980 |
JPX |
206930 |
Dec 1982 |
JPX |
60-190160 |
Feb 1986 |
JPX |
496282 |
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CHX |
1206213 |
Sep 1970 |
GBX |
2040121 |
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GBX |
Non-Patent Literature Citations (3)
Entry |
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Continuations (1)
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Number |
Date |
Country |
Parent |
839304 |
Mar 1986 |
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