1. A thermostat comprising:
a switch having contacts;
a sensor generating a force to operate the switch in response to an ambient temperature;
a lever provided with an arm, the lever turning with the force from the sensor to openclose the contacts of the switch;
a spring having a first end hooked to the lever and a second end, the spring biasing a force to the lever in a direction opposite to the force from the sensor; and
a control plate hooked to the second end of the spring and disposed on the lever, the control plate increasingdecreasing a force required for turning the lever due to turning of the control plate,
wherein the arm turns together with the control plate to open the contacts of the switch when the control plate turns at more than a predetermined angle.
2. The thermostat of claim 1,
wherein the sensor has a capillary tube including a gas that expandscontracts in response to an ambient temperature, and a bellows that converts volume changes of the gas into the force to operate the switch.
3. The thermostat of claim 1, further comprising
a cam plate to turn the control plate.
4. The thermostat of claim 1,
wherein the lever further has:
a first vertical member to receive the force from the sensor;
a horizontal member perpendicular to the first vertical member;
a second vertical member disposed on a side identical to the arm according to the horizontal member and hooked with the first end of the spring; and
a spacer disposed on the horizontal member on a side opposite to the second vertical member, the spacer operating the switch,
and the lever turns around an end of the first vertical member.
5. The thermostat of claim 1,
wherein an axis of turning of the control plate and an axis of turning of the lever are disposed in parallel with each other.
6. The thermostat of claim 1,
wherein the arm has a ridge provided on a side facing the control plate, the ridge making contact with the control plate.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A power conversion circuit with shorted lamp detection for driving at least one fluorescent lamp, the circuit comprising:
an inverter configured to receive a substantially direct current input voltage and to generate an alternating current lamp voltage to drive the fluorescent lamps; and
a shorted lamp detector configured to monitor the alternating current lamp voltage and to generate a feedback voltage with an amplitude proportional to the amplitude of the lame voltage, wherein the shorted lamp detector produces periodic pulses if the amplitude of the feedback voltage is above a predefined threshold to indicate normal operations and produces a substantially direct current voltage if the amplitude of the feedback voltage is below the predefined threshold to detect a shorted lamp condition.
2. The power conversion circuit of claim 1, wherein the inverter comprises:
a primary network configured to receive the substantially direct current input voltage;
a controller configured to output driving signals to the primary network to generate an alternating current signal in the primary network; and
a secondary network coupled to the primary network and configured to output the alternating current lamp voltage.
3. The power conversion circuit of claim 2, wherein the controller is disabled when the shorted lamp condition lasts longer than a predetermined duration.
4. A power conversion circuit with shorted lame detection for driving at least one fluorescent lamp, the circuit comprising:
an inverter configured to receive a substantially direct current input voltage and to generate an alternating current lamp voltage to drive the fluorescent lamps, wherein the inverter comprises:
a primary network configured to receive the substantially direct current input voltage;
a controller configured to output driving signals to the primary network to generate an alternating current signal in the primary network; and
a secondary network coupled to the primary network and configured to output the alternating current lamb voltage;
a shorted lamp detector configured to monitor the alternating current lamp voltage to detect a shorted lamp condition; and
a voltage sensing feedback circuit coupled to the output of the secondary network to sense the alternating current lamp voltage and to generate a voltage feedback signal with an amplitude proportional to the amplitude of the alternating current lamp voltage for the shorted lamp detector.
5. The power conversion circuit of claim 4, wherein the voltage sensing feedback circuit is a capacitive voltage divider.
6. The power conversion-circuit of claim 4, wherein the voltage sensing feedback circuit is a resistive voltage divider.
7. The power conversion circuit of claim 4, wherein the shorted lamp detector comprises:
an open collector comparator coupled to the output of the voltage sensing feedback circuit;
a holding capacitor coupled to the output of the open collector comparator;
a pull-up resistor coupled to the output of the open collector comparator; and
a reference comparator coupled to the output of the open collector comparator.
8. The power conversion circuit of claim 4, wherein the shorted lamp detector comprises:
a high voltage detector coupled to the output of the voltage sensing feedback circuit;
a conditioning circuit coupled to the output of the high voltage detector; and
a threshold detector coupled to the output of the conditioning circuit.
9. The power conversion circuit of claim 8, wherein the high voltage detector is a single transistor amplifier.
10. The power conversion circuit of claim 8, wherein the conditioning circuit comprises:
a half-wave rectifier;
a timing resistor; and
a charging capacitor.
11. The power conversion circuit of claim 8, wherein the threshold detector is a comparator.
12. A method for detecting a shorted lamp condition in a backlight system, the method comprising the acts of:
sensing a lamp voltage provided by an inverter to drive at least one fluorescent lamp in the backlight system;
generating a feedback voltage with an amplitude proportional to the amplitude of the lamp voltage;
generating periodic pulses if the amplitude of the feedback voltage is above a predefined threshold indicative of normal operations; and
generating a substantially direct current voltage if the amplitude of the feedback voltage is below the predefined threshold indicative of the shorted lamp condition.
13. The method of claim 12 further comprising the act of disabling the inverter when the shorted lamp condition lasts longer than a predetermined duration.