Low current thyristor-based dimming
Various apparatuses and methods for starting a thyristor are disclosed herein. For example, some embodiments provide an apparatus for controlling power to a load. The apparatus includes a thyristor, a secondary load switchably connected to an output of the thyristor, and a sensor connected to the secondary load. The sensor is adapted to connect the secondary load to the thyristor when the output of the thyristor falls below a predetermined level.
1. An apparatus for controlling power to a load, the apparatus comprising:
a thyristor;
a secondary load switchably connected to an output of the thyristor; and
a sensor connected to the secondary load, wherein the sensor is adapted to connect the secondary load to the thyristor when the output of the thyristor falls below a predetermined level, wherein the secondary load is switchably connected to the thyristor output by a transistor, wherein the sensor comprises:
a resistor connected between the thyristor output and a control input of the transistor, and a second resistor connected between the control input of the transistor and a low voltage reference node;
a Zener diode connected to the control input of the transistor;
a second transistor having an input connected to the control input of the transistor;
a third resistor connected between the thyristor output and a control input of the second transistor, and a fourth resistor connected between the control input of the second transistor and the low voltage reference node; and
a second Zener diode connected to the control input of the second transistor.
2. The apparatus of claim 1 , further comprising a lamp base, wherein the secondary load and sensor are located within the lamp base.
3. The apparatus of claim 1 , wherein the secondary load comprises a resistor having a resistance below about 10 kilohms.
4. The apparatus of claim 1 , wherein the secondary load comprises at least one member selected from the group consisting of a motor, a fan, an incandescent light, an electrical charger, and an air freshener.
5. The apparatus of claim 1 , wherein the secondary load is switchably connected to the thyristor output by the second transistor.
6. The apparatus of claim 1 , further comprising a delay element connected to the second transistor.
7. The apparatus of claim 6 , wherein the delay element comprises a capacitor connected to the fourth resistor.
8. The apparatus of claim 1 , wherein the secondary load remains connected to the output of the thyristor while the output of the thyristor remains below the predetermined level.
9. The apparatus of claim 1 , wherein the transistor has a voltage rating based on a peak voltage at the output of the thyristor.
10. The apparatus of claim 1 , wherein the Zener diode is operable to prevent a gate to source voltage on the transistor from rising above a maximum rated gate to source voltage for the transistor.
11. The apparatus of claim 1 , wherein the secondary load is switchably connected to the output of the thyristor through a rectifier.
12. The apparatus of claim 1 , wherein the secondary load is switchably connected to the output of the thyristor through a half-bridge rectifier.
13. The apparatus of claim 12 , wherein the half-bridge rectifier comprises a pair of diodes.
14. The apparatus of claim 13 , wherein the pair of diodes are oriented in a same direction.
15. The apparatus of claim 1 , wherein the secondary load comprises an incandescent light.
16. The apparatus of claim 1 , wherein the secondary load comprises a heater.
17. The apparatus of claim 1 , wherein the secondary load comprises a resistor.
18. The apparatus of claim 1 , wherein the third resistor and the fourth resistor have values selected to turn on the second transistor when the output of the thyristor is at a full power level.
19. The apparatus of claim 1 , wherein the second transistor has a voltage rating based on a maximum gate voltage of the transistor.
20. The apparatus of claim 19 , wherein the maximum gate voltage of the transistor is based on the Zener diode.