Emergency lighting system with high efficiency inverter

Claim 2

An emergency lighting circuit for operating at least one gaseous discharge lamp comprising: means for coupling to an AC energy source for energizing the lamp during normal conditions when the Ac source voltage is above a predetermined value; means including a tuned inverter for operating the lamp during emergency conditions when the AC source voltage is below a predetermined value, the inverter having a pair of transistors capable of operation in a low loss switching mode; means enabling the transistors to operate in the low loss switching mode; a control circuit supplying base drive for switching the transistors at zero collector voltage thereof; and means providing timing information to the control circuit for effecting switching of the respective transistors in step with a natural resonant frequency of the inverter.

Claim 3

The circuit of claim 1 further including means providing a feedback current to the control circuit to effect transistor base drive proportional to transistor collector current.

Claim 4

The circuit of claim 2 wherein the feedback current providing means is a feedback winding magnetically coupled to the respective collectors of the transistors.

Claim 5

The circuit of claim 2 wherein the control circuit includes a zero crossing detector receiving the feedback current from the feedback current providing means and a pair of output drivers connected to the zero crossing detector for driving the respective transistors.

Claim 6

The circuit of claim 1 further including an auxiliary electrical energy source.

Claim 7

The circuit of claim 5 including a first transformer coupling the inverter with the lamp and wherein the means enabling the transistors is a buffer inductance electrically connected serially between the auxiliary electrical energy source and a center tap of a primary winding of the first transformer.

Claim 8

The circuit of claim 6 wherein the means providing timing information is an auxiliary winding magnetically coupled with the primary winding of the first transformer.

Claim 9

The circuit of claim 5 wherein the control circuit further includes: a first sensor for sensing the voltage of the AC energy source; a second sensor for sensing the voltage of the auxiliary electrical energy source; logic means for combining the outputs of the first sensor and the second sensor to enable the inverter when the auxiliary source voltage is above a predetermined level and the AC source voltage is below a predetermined level and to disable the inverter when the auxiliary source voltage is below a predetermined level or the AC source voltage is above a predetermined level.

Claim 10

The circuit of claim 1 further comprising: voltage clamping means for limiting the voltage transient resulting when both transistors switch off.

Claim 11

The circuit of claim 1 wherein the inverter is energized by a battery.

Claim 12

The circuit of claim 10 further including means for charging the battery.

Claim 13

The circuit of claim 11 further including means for limiting the voltage transient resulting when the battery is disconnected while the charging means is operating.

Claim 14

An emergency lighting circuit for operating at least one gaseous discharge lamp comprising: a first transformer coupling the circuit with an AC voltage source for energizing the lamp during normal conditions when the AC voltage is above a predetermined value, the first transformer having a primary winding and at least one secondary winding; means including a tuned inverter for operating the lamp during emergency conditions when the AC source voltage is below a predetermined value, the inverter having a pair of transistors capable of operation in a low loss switching mode; a second transformer coupling the inverter with the lamp, the transformer including a primary winding having a center tap; a capacitance connected in parallel across the second transformer primary, the combination serving to set the natural resonant freQuency of the inverter when the lamp is disconnected therefrom; a battery for energizing the inverter under predetermined conditions; a buffer impedance connected serially between the battery and the second transformer center tap for enabling the transistors to operate in the low loss switching mode; a control circuit supplying base drive for switching the transistors at zero collector voltage thereof; an auxiliary winding magnetically coupled with the second transformer primary winding to provide timing information to the control circuit for effecting switching of the respective transistors in step with the natural resonant frequency of the inverter; a feedback winding magnetically coupled to the respective collectors of the traansistors to provide a feedback current to the control circuit for effecting transistor base drive proportional to transistor collector current; the control circuit including a zero crossing detector receiving the feedback current from the feedback winding and a pair of output drivers connected to the zero crossing detector for driving the respective transistors; the control circuit further indcluding a first sensor for sensing the voltage of the AC source, a second sensor for sensing the voltage of the battery and logic means combining the outputs of the first and second sensors to enable the inverter when the battery voltage is above a predetermined level and the AC source voltage is below a predtermined level and to disable the inverter when the battery voltage is below a predetermined level or the AC source voltage is above a predetermined level.

Claim 15

An emergency lighting circuit for operating at least one gaseous discharge lamp comprising: a first transformer coupling the circuit with an AC voltage source for energizing the lamp during normal conditions when the AC voltage is above a predetermined value, the first transformer having a primary winding and at least one secondary winding; means including a tuned inverter for operating the lamp during emergency conditions when the AC source voltage is below a predetermined value, the inverter having a pair of transistors capable of operation in a low loss switching mode; a second transformer coupling the inverter with the lamp, the transformer including a primary winding having a center tap; a capacitance connected in parallel across the second transformer primary, the combination serving to set the natural resonant freQuency of the inverter when the lamp is disconnected therefrom; a battery for energizing the inverter under predetermined conditions; a buffer impedance connected serially between the battery and the second transformer center tap for enabling the transistors to operate in the low loss switching mode; a control circuit supplying base drive for switching the transistors at zero collector voltage thereof; an auxiliary winding magnetically coupled with the second transformer primary winding to provide timing information to the control circuit for effecting switching of the respective transistors in step with the natural resonant frequency of the inverter; a feedback winding magnetically coupled to the respective collectors of the traansistors to provide a feedback current to the control circuit for effecting transistor base drive proportional to transistor collector current; the control circuit including a zero crossing detector receiving the feedback current from the feedback winding and a pair of output drivers connected to the zero crossing detector for driving the respective transistors; the control circuit further indcluding a first sensor for sensing the voltage of the AC source, a second sensor for sensing the voltage of the battery and logic means combining the outputs of the first and second sensors to enable the inverter when the battery voltage is above a predetermined level and the AC source voltage is below a predtermined level and to disable the inverter when the battery voltage is below a predetermined level or the AC source voltage is above a predetermined level.

Claim 16

A tuned inverter for energizing a load comprising: a pair of transistors capable of operation in a low loss switching mode; means enabling the transistors to operate in the low loss switching mode; a control circuit supplying base drive for switching the transistors at zero collector voltage thereof; and means providing timing information to the control circuit for effecting switching of the respective transistors in step with a natural resonant frequency of the inverter.

Claim 17

A tuned inverter for energizing a load comprising: a pair of transistors capable of operation in a low loss switching mode; means enabling the transistors to operate in the low loss switching mode; a control circuit supplying base drive for switching the transistors at zero collector voltage thereof; and means providing timing information to the control circuit for effecting switching of the respective transistors in step with a natural resonant frequency of the inverter.

Claim 18

The inverter of claim 14 further including means providing a feedback current to the control circuit to effect transistor base drive proportional to transistor collector current.

Claim 19

The inverter of claim 15 wherein the feedback current providing means is a feedback winding magnetically coupled to the respective collectors of the transistors.

Claim 20

The inverter of claim 15 wherein the control circuit includes a zero crossing detector receiving the feedback current from the feedback current providing means and a pair of output drivers connected to the zero crossing detector for driving the respective transistors.

Claim 21

The inverter of claim 14 further including an auxiliary electrical energy source.

Claim 22

The inverter of claim 18 including a first transformer coupling the inverter with the load wherein the means enabling the transistors is a buffer inductance electrically connected serially between the auxiliary electrical energy source and a center tap of a primary winding of the first transformer.

Claim 23

The inverter of claim 19 further comprising means for coupling to a first electrical energy source including a second transformer having a primary winding and at least one secondary winding.

Claim 24

The inverter of claim 20 wherein the means providing timing information is an auxiliary winding magnetically coupled with the primary winding of the first transformer.

Claim 25

The inverter of claim 18 wherein the control circuit further includes: a first sensor sensing the voltage of the first electrical energy source; a second sensor sensing the voltage of the auxiliary electrical energy source; logic means combining the outputs of the first and second sensors to enable the inverter when the auxiliary source voltage is above a predetermined level and the first source voltage is below a predetermined level and to disable the inverter when the auxilIary source voltage is below a predetermined level or the first source voltage is above a predetermined level.

Claim 26

The inverter of claim 14 further comprising: voltage clamping means for limiting the voltage transient resulting when both transistors switch off.

Claim 27

The inverter of claim 14 wherein a battery serves as a source of electrical energy for the inverter.

Claim 28

The inverter of claim 24 further including means for charging the battery.