U.S. patent number 3,573,541 [Application Number 04/817,997] was granted by the patent office on 1971-04-06 for transistor-controlled emergency exit unit.
This patent grant is currently assigned to Robert O. Dunn. Invention is credited to Robert O. Dunn, Joseph R. Dydynski, Jerry D. Haney, David C. Wilton.
United States Patent |
3,573,541 |
Dunn , et al. |
April 6, 1971 |
TRANSISTOR-CONTROLLED EMERGENCY EXIT UNIT
Abstract
A changeover device for an emergency exit unit having lamps with
AC filaments normally operated by a main power supply and normally
unenergized DC filaments for operation by a standby battery, which
is normally kept charged by a charger circuit. A transistor
circuit, when conductive, sends power from the battery to the DC
filaments, but the circuit provides for reverse-biasing the base of
the transistor while the main power supply is on. An electric
charge is created and stored while the main power supply is on, and
upon discharge sends bias voltage to the transistor to make it
conductive. Self-holding means is energized by the same discharge
through said transistor, for retaining the connection between the
battery and the DC filaments, and the self-holding means is
released when the voltage of the battery drops a predetermined
amount below normal, thereby disconnecting the battery from said DC
filaments and preventing further battery discharge.
Inventors: |
Dunn; Robert O. (El Sobrante,
CA), Wilton; David C. (Los Altos, CA), Dydynski; Joseph
R. (Cupertino, CA), Haney; Jerry D. (Sunnyvale, CA) |
Assignee: |
Dunn; Robert O. (El Sobrante,
CA)
|
Family
ID: |
25224364 |
Appl.
No.: |
04/817,997 |
Filed: |
April 21, 1969 |
Current U.S.
Class: |
315/87; 307/23;
307/39; 307/66; 315/92; 315/127; 315/175 |
Current CPC
Class: |
H02J
7/007182 (20200101); H02J 9/02 (20130101); H02J
7/008 (20130101); G08B 7/062 (20130101) |
Current International
Class: |
H02J
9/00 (20060101); H02J 7/00 (20060101); H02J
9/02 (20060101); G08B 5/22 (20060101); G08B
5/36 (20060101); H05b 039/06 (); H05b 043/00 () |
Field of
Search: |
;307/23,39,64,66,86,126,130,131,142
;315/86,87,88,92,127,160,173,175,200,227 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kominski; John
Assistant Examiner: LaRoche; E. R.
Claims
We claim:
1. A changeover device for an emergency exit unit having lamps with
AC filaments normally operated by a main power supply and normally
unenergized DC filaments, and having a standby battery, including
in combination:
transistor means, which, when conductive, sends power from said
battery to said DC filaments;
bias means for reverse-biasing the base of said transistor means
while said main power supply is on, to render it nonconducting;
charge means for creating and storing an electric charge while said
main power supply is on, said charge means upon discharge sending
bias voltage to said transistor means to make it conductive;
self-holding means energized by discharge of said charge means
through said transistor means for retaining said connection between
the battery and said DC filaments; and
release means for releasing said self-holding means when the
voltage of said battery drops a predetermined amount below normal,
thereby disconnecting said battery from said DC filaments and
preventing further battery discharge.
2. The device of claim 1 having battery-charging means connected to
said battery and to said main power supply for keeping said battery
charged while said main power supply is operative.
3. The device of claim 2 wherein said battery-charging means
includes a silicon-controlled rectifier SCR in series with and
between said battery and said main power supply and having a gate
bias provided across a zener diode and resistance means.
4. The device of claim 3 wherein a diode protects the SCR gate from
reverse voltages in excess of the SCR gate-cathode threshold
voltage.
5. The device of claim 1 wherein said transistor means comprises a
main transistor and said self-holding means comprises a pair of
transistors comprising a complementary regenerative circuit with
latching action for said main transistor to provide base current to
said main transistor sufficient to saturate said main transistor
when said main power supply is off and thereby to provide a
low-resistance path from said battery to said DC filaments.
6. The device of claim 1 having release means for releasing said
self-holding means when the voltage of said battery drops a
predetermined amount below the normal voltage of said battery,
thereby disconnecting said battery from said DC filaments and
preventing further battery discharge.
7. A changeover device for an emergency exit unit having lamps with
AC filaments normally operated by a main power supply and normally
unenergized DC filaments, and having a standby battery, including
in combination:
a battery charger for said battery for retaining the strength of
said battery when the main power supply is on, and a complementary
bistable circuit comprising;
a transistor for sending power from said battery to said DC
filaments when its base is forwardly biased;
reverse-bias means connected to the base of said transistor while
said main power supply is on to render said transistor
nonconductive;
capacitor means for creating and storing an electric charge while
said main power supply is on, said capacitor means upon discharge
sending forward bias voltage to said transistor to make it
conductive;
self-holding means energized by discharge of said capacitor means
through said transistor for retaining the connection between the
battery and said DC filaments; and
release means for releasing said self-holding means when the
voltage of said battery drops a predetermined amount below normal,
thereby disconnecting said battery from said DC filaments and
preventing further battery discharge.
8. The device of claim 7 wherein said self-holding means comprises
a pair of additional transistors comprising a complementary
regenerative circuit to provide base current to the aforesaid
transistor sufficient to saturate it and thereby latch it on when
said main power supply is off.
9. An automatic changeover device for a unit normally operated by a
main AC power supply and having a standby battery, including in
combination:
transistor means, which, when conductive, sends power from said
battery to said unit;
bias means for reverse-biasing the base of said transistor means
while said main power supply is on, to render it nonconducting;
charge means for creating and storing an electric charge while said
main power supply is on, said charge means upon discharge sending
bias voltage to said transistor means to make it conductive;
self-holding means energized by discharge of said charge means
through said transistor means for retaining said connection between
the battery and said unit; and
release means for releasing said self-holding means when the
voltage of said battery drops a predetermined amount below normal,
thereby disconnecting said battery from said unit and preventing
further battery discharge.
10. The device of claim 9 having battery-charging means connected
to said battery and to said main power supply for keeping said
battery charged while main power supply is operative.
11. The device of claim 10 wherein said battery-charging means
includes a silicon-controlled rectifier SCR in series with and
between said battery and said main power supply and having a gate
bias provided across a zener diode and resistance means.
12. The device of claim 11 wherein a diode protects the SCR gate
from reverse voltages in excess of the SCR gate-cathode threshold
voltage.
13. The device of claim 9 wherein said transistor means comprises a
main transistor and said self-holding means comprises a pair of
transistors comprising a complementary regenerative circuit with
latching action for said main transistor to provide base current to
said main transistor sufficient to saturate said main transistor
when said main power supply is off and thereby to provide a
low-resistance path from said battery to said unit.
14. The device of claim 9 having release means for releasing said
self-holding means when the voltage of said battery drops a
predetermined amount below the normal voltage of said battery,
thereby disconnecting said battery from said unit and preventing
further battery discharge.
15. A changeover device for a unit normally operated by a main AC
power supply having a standby battery, including in
combination:
a battery charger for said battery for retaining the strength of
said battery when the main power supply is on, and a complementary
bistable circuit comprising;
a transistor for sending power from said battery to said unit when
its base is forwardly biased;
reverse-bias means connected to the base of said transistor while
said main power supply is on to render said transistor
nonconductive;
capacitor means for creating and storing an electric charge while
said main power supply is on, said capacitor means upon discharge
sending forward bias voltage to said transistor to make it
conductive;
self-holding means energized by discharge of said capacitor means
through said transistor for retaining the connection between the
battery and said unit; and
release means for releasing said self-holding means when the
voltage of said battery drops a predetermined amount below normal,
thereby disconnecting said battery from said unit, and preventing
further battery discharge.
16. The device of claim 15 wherein said self-holding means
comprises a pair of additional transistors comprising a
complementary regenerative circuit to provide base current to the
aforesaid transistor sufficient to saturate it and thereby latch it
on when said main power supply is off.
Description
This invention relates to emergency exit lights. More particularly,
the invention relates to an improved emergency light or sign with a
self-contained auxiliary power source for operating the light or
sign when the normal power supply fails.
The exit lights required in theaters and auditoriums are normally
lighted by the public power supply. However, some of the conditions
which give rise to emergencies or are caused by them, cut off this
power supply at the time when the lights are most needed. As a
result, many governmental units have promulgated fire and safety
regulations requiring that emergency lighting and signs, including
exit signs, have auxiliary power available at all times to operate
them in the absence of their conventional power supply. However,
currently available auxiliary power sources have been bulky, have
been expensive to install, and have been expensive to maintain in
good working order. Many of the attempts to meet these requirements
have proved either unsuccessful or so expensive that authorities
have sometimes winked at their own regulations and have allowed
people to get by with less than what the law requires. In other
instances, a severe financial burden has been placed upon those
complying with the requirements, and with none too satisfactory
operation either.
The present invention is addressed to the solution of this problem
by a compact and relatively low-cost device providing an
inexpensive, easily maintained auxiliary power source with
automatic switching from the normal power supply to the auxiliary
power supply. An important feature of the invention is that the
entire combination of exit sign, exit lights, and auxiliary power
supply need be very little larger, if any, than standard exit signs
having only the normal power supply. Another feature of the
invention is that the device consumes an insignificant amount of
power in keeping the auxiliary power supply in working order.
A very important feature is that the device automatically shuts
itself off when it has been on long enough to begin substantial
depletion of the battery; so that the battery can recover for reuse
without being drained.
Other objects and advantages of the invention will become apparent
from the following description of a preferred form thereof.
In the drawings:
FIG. 1 is a fragmentary view in perspective of an exit door having
an exit unit embodying the principles of this invention mounted
above the door and including both an exit sign and emergency
lighting shining down on the floor, as well as the auxiliary power
supply and switching circuits.
FIG. 2 is a simplified electrical circuit diagram for the sign of
FIG. 1.
FIG. 3 is an electrical circuit diagram of the circuit board
element of FIG. 2.
FIG. 4 is a view in elevation on a reduced scale of the unit of
FIG. 1 with the front wall removed.
The invention comprises a housing 10, which may be made from cast
aluminum, with a translucent exit panel 11 on at least one main
wall 12 and a translucent panel 13 in a bottom wall 14 for
down-lighting. The translucent exit panel may be replaced with
other panels for emergency signs of other kinds or with translucent
panels for illumination, and there may be minor modifications; for
example, the sign or light may be either surface, pendant, or end
mounted.
Under normal conditions the sign is lighted from house current
coming in through lines 15 and 16, shown in FIG. 2, to the primary
17 of a transformer 18 inside the housing 10. A test switch 19 is
provided in the line 15. From a secondary 20, a tapped lead 21 goes
to AC filaments 22 and 23 of dual-filament lamps 24 and 25,
returning through leads 26, 27, 28, and 29, via a circuit board 30,
all inside the housing 10.
In parallel across the primary 17, is a power indicating light 31
which illuminates a dim panel 32 when the normal power supply is
on. If the lights 24 and 25 go out and the light 31 is still on,
the trouble is not with the power supply but with the internal
circuit.
The auxiliary power supply is preferably a rechargeable battery 33,
such as a nickel-cadmium battery, also inside the housing 10.
Normally, the battery 33 is kept in standby conditions and is not
used but is kept charged by a battery charging circuit, described
below; a charge indicator 34 indicates when the battery 33 is being
charged. No power is drawn from the battery 33 except when the main
power supply fails or is cut off from the transformer 18; then a
changeover circuit, described below, puts the battery 33 into the
lamp circuit, via a lead 35 and leads 26 and 27, to light DC
filaments 36 and 37 of the lamps 24 and 25, with return leads 38
and 39 going to the circuit board 31, which is connected to the
battery 33 by a lead 40 (via a transfer transistor 60, as explained
below) and to the charge indicator 32 by leads 41 and 42 (via a
charging SCR 50, as explained below). A lead 43 goes from the
circuit board 30 to the transformer secondary 20.
The circuit indicated by the schematic diagram of FIG. 2 and the
wiring diagram of FIG. 3 performs three basic functions: namely,
(1) battery charging, (2) transfer from AC power to battery power
upon interruption of the AC line power, and (3) disconnecting the
battery 33 when the battery voltage has discharged to a minimum
recommended value, determined by battery life considerations. For
these purposes, the circuit board 30 comprises a battery charger
circuit 44 and a complementary bistable circuit 45. (See FIG.
3)
Battery charging current is provided to the charge circuit 44 from
the full voltage of the transformer secondary 20 via a silicon
controlled rectifier SCR 50, which is connected across the leads 40
and 42, and a current limiting resistor 51 connected to the lead 42
and the SCR 50. When the terminal voltage of the battery 33 is
below the gate threshold voltage of the SCR 50, the SCR 50 conducts
on each half-cycle of the transformer secondary voltage. The SCR
gate voltage is determined by the voltage across a zener diode 52
as divided by resistors 53, 54, and 55. The resistor 53 serves as a
source of current to the zener diode 52. A diode 56 protects the
SCR gate from reverse voltages in excess of the SCR gate-cathode
ratings. As the battery voltage builds up to the SCR gate-cathode
threshold voltage, the SCR 50 ceases to conduct, and charging
current is reduced to zero. Charge indication is provided by the
lamp 34, which is connected across the current limiting resistor
51.
Turning now to the complementary bistable circuit 45, sign
illumination is normally provided by the tapped transformer
secondary voltage as supplied to the AC filaments 22 and 23 of the
two lamps 24 and 25. Battery voltage is not impressed across the DC
filaments 36 and 37 as long as a series PNP transistor 60, which is
part of the circuit 45, is nonconducting. When AC power is present,
a positive DC voltage is present at the base of the transistor 60,
which is developed by half-wave rectification of the transformer
secondary voltage via a rectifier 61. This rectified voltage is
filtered by a capacitor 62 and applied to the base of the
transistor 60 via a diode 63 and a resistor 64. A resistor 65
provides a path for collector-to-base leakage current of the
transistor 60. The positive voltage present at the base of the
transistor 60 is then higher than the battery voltage; thus, the
base-emitter junction of the transistor 60 is reversed-biased, as
is the base-emitter junction of a PNP transistor 66, and this
insures that both of these PNP-type transistors are nonconducting
when a AC power is present.
A third transistor 67 is at this time also rendered nonconducting
by the negative base-emitter voltage developed by a rectifier diode
68 and a filter capacitor 69. This negative voltage across the
capacitor 69 is divided down to the base of the transistor 67 via
resistors 70, 71, and 72. These resistors 70, 71, and 72, in
conjunction with a resistor 73, are chosen such that the resultant
base voltage of the transistor 67 is negative in sign, even though
a positive voltage source is present across the capacitor 62. A
diode 74 protects the base-emitter junction of the transistor 67
against reverse voltages in excess of maximum ratings. A resistor
75 lies between the base of the transistor 66 and the base of the
transistor 60, and between the collector of the transistor 67 and
the base of the transistor 60.
When the AC power is interrupted, as by power failure or by
throwing the test switch 19, the positive DC voltage across the
transistor 67 and the negative voltage across the capacitor 69
begin to decrease at a rate determined by the values of the
capacitors and the resistors in the discharge paths. These time
constants are chosen so that the negative voltage diminishes before
the positive voltage. Presence of a positive voltage on the base of
the transistor 67 causes the collector current to flow into the
bases of both of the transistor 60 and 66. The transistors 66 and
67 comprise a complementary regenerative circuit providing a
latching action which holds the transistor 66 on, thus providing
base current to transistor 60 sufficient to saturate this
transistor. With the transistor 60 saturated, a low-resistance path
is provided from the battery 33 to the DC lamp filaments 36 and 37.
The circuit has, thus, transferred battery power to the lamps when
AC power is interrupted. When AC power returns, the reverse-bias
conditions are again present, and the battery is disconnected from
the lamps, while the AC lamp filaments are again lighted.
When the circuit is in the "on" state, the base current of the
transistor 67 is provided from the battery 33, via a resistor 76
and the transistor 66. The transistor 66 is in saturation from base
current provided by the transistor 67. The current from the battery
33 via the resistor 76 is divided at the base of the transistor 67
by the ratio of the values of a resistor 77 (in parallel with the
total series resistance of the resistors 70, 71, and 73), to the
resistor 76. When the battery voltage falls below a level where the
base current into the transistor 67 is insufficient to maintain
saturation of the transistor 67, its collector current begins to
decrease, thereby reducing the base current into the transistor 66.
When the base current into the transistor 66 is insufficient to
hold the transistor 66 in saturation, the transistor 66 becomes
less conductive, and the current from its collector decreases. The
effect is regenerative and the transistors 66, 67, and 60 turn off,
and the battery 33 is thereby disconnected from the lamp filaments
36 and 37. For a nickel-cadmium battery 33, the resistor 70 is
adjusted so that this disconnect threshold is normally 87 percent
of the normal battery terminal voltage, which is the level
suggested by the manufacturer to accommodate maximum battery
life.
Typical characteristics of the circuit of FIG. 3 are as
follows:
Transistors:
60 PNP 2N 3613
66 pnp 2n 3638
67 pnp 2n 3569
rectifiers:
56 A 14F
61 a14f
63 a 14f
68 a 14f
74 a 14f
scr 50 2n 4441
capacitors:
62 100 mf., 35 v.
69 50 mf., 25 v.
Resistors:
51 5 ohms
52 270 ohms
54 47 ohms
55 1000 ohms
64 2700 ohms
65 2200 ohms
70 100 ohms
71 270 ohms
72 1500 ohms
73 1500 ohms
75 27 ohms
76 27 ohms
77 220 ohms
To those skilled in the art to which this invention relates, many
changes in construction and widely differing embodiments and
applications of the invention will suggest themselves without
departing from the spirit and scope of the invention. The
disclosures and the description herein are purely illustrative and
are not intended to be in any sense limiting.
* * * * *