U.S. patent number 3,723,852 [Application Number 05/250,592] was granted by the patent office on 1973-03-27 for output voltage adjusting circuit.
This patent grant is currently assigned to The Superior Electric Company. Invention is credited to Irving J. Giguere, Thomas G. Peterson.
United States Patent |
3,723,852 |
Peterson , et al. |
March 27, 1973 |
OUTPUT VOLTAGE ADJUSTING CIRCUIT
Abstract
A circuit connectible to an integrated circuit fixed voltage
D.C. regulator for providing an adjustable value of output voltage
to a load, especially a load consisting of an incandescent
lamp.
Inventors: |
Peterson; Thomas G. (Bristol,
CT), Giguere; Irving J. (Bristol, CT) |
Assignee: |
The Superior Electric Company
(Bristol, CT)
|
Family
ID: |
22948380 |
Appl.
No.: |
05/250,592 |
Filed: |
May 5, 1972 |
Current U.S.
Class: |
323/224; 315/207;
315/311 |
Current CPC
Class: |
G05F
1/56 (20130101) |
Current International
Class: |
G05F
1/56 (20060101); G05F 1/10 (20060101); G05f
001/60 () |
Field of
Search: |
;315/207,311 ;321/18
;323/8,22T,23,25 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pellinen; A. D.
Claims
We claim:
1. An adjustable D.C. voltage regulating circuit connectible to a
D.C. input source for providing an output voltage adjustable in
value comprising a semiconductor voltage regulator means having an
input, output and common terminals and having the input terminal
being connectible to the positive input source to provide a
constant value of voltage between the common and the output
terminals with the common terminal being negative with respect to
the output terminal and with a quiescent current normally flowing
from the common terminal, a potential divider connected between the
output terminal and the ground of the source and across which the
desired value of output voltage appears, said divider including an
adjustable resistance having a tap with a first portion being
connected between the output terminal and the tap and a second
portion being connected between the tap and the ground,a shunt path
connected between the common terminal and the ground and means for
maintaining a selected value of voltage across the first portion of
the divider.
2. The invention as defined in claim 1 in which the shunt path
includes a transistor having an emitter collector path with the
emitter being connected to the common terminal and with the emitter
collector path being connected between the said common terminal and
the ground.
3. The invention as defined in claim 2 in which there are means for
causing the transistor to be conducting during the flow of
quiescent current and the shunt path carries substantially all of
the quiescent current.
4. The invention as defined in claim 1 in which the shunt path has
a transistor connected as in an emitting follower connection, means
for placing a fixed value of voltage from the output terminal at
the emitter and in which the selected value of voltage is the fixed
value less the diode voltage drop between the base and emitter of
the transistor.
5. The invention as defined in claim 1 in which the last named
means includes a transistor, a connection between the tap and the
base of the transistor and a resistor connected between the output
terminal and the emitter of the transistor.
Description
In many applications it has been found advantageous to use
currently commercially available integrated circuit devices for
providing a regulated voltage in a circuit. These regulators have a
fixed value of output voltage but if used with an external circuit
a voltage may be obtained that is adjustable in value with the
value of the fixed voltage being the minimum value in the
adjustment range. However, such suggested circuits have sometimes
not provided a sufficient range of adjustability and if used to
adjust the voltage to an incandescent lamp load for varying the
intensity thereof have even been found to be incapable of
operating.
It is accordingly an object of the present invention to provide a
circuit usable with an IC fixed voltage regulator which enables the
regulator to be accurately adjustable over a wide range of output
voltages.
Another object of the present invention is to provide an IC fixed
voltage regulator with an adjustable circuit that enables the
regulator to reliably function with a load that has a low
resistance when cold such as a lamp load.
A further object of the invention is to achieve the above objects
with a circuit that is reliable in use, relatively inexpensive,
easily incorporated with a regulator and significantly less power
consuming and heat producing.
The present invention is usable with a commercially available
integrated circuit that is formed to provide a fixed value of
output voltage such as a type LM309 available from National
Semiconductor Corporation, 2900 Semiconductor Drive, Santa Clara,
California; or uA7800 series regulator currently commercially
available from Fairchild Semiconductor (a division of Fairchild
Camera and Instrument Corporation) 313 Fairchild Drive, Mountain
View, California. These devices have three terminals designated
input, output and common with the voltage from a D.C. source being
applied between the input and the common terminals and a fixed or
regulated value (such as 5 volts) of D.C. being obtained between
the output and the common terminals. It has heretofore been
suggested to connect a resistance network between the output
terminal and the negative side of the input source with one portion
of the network being connected between the output and the common
terminals and the other portion being variable and connected
between the common terminal and the negative side in order to
obtain an adjustable value of voltage greater than that produced by
the regulator across the resistance network.
In accordance with the present invention, there is also provided a
resistance network which has the form of a potential divider
connected in parallel across the output and negative side together
with a shunt path. The divider includes an adjustable resistance
having a tap such that by varying the tap the resistance portions
on each side thereof may be relatively varied and in doing so
varying the output of the regulator by altering the relative
resistances in the two portions. However, connected across the
divider and to the common terminal is a shunt path having a
transistor whose emitter collector path is connected to the common
terminal and with its base being connected to the tap. Accordingly,
with the present invention, variation of the output voltage is
achieved by varying the current in the potential divider as opposed
to the concept of varying the relative resistances with constant
current as in the heretofore suggested circuit.
Other features and advantages will hereinafter appear.
Referring to the drawing:
FIG. 1 is a diagrammatic and schematic illustration of a prior art
adjustable voltage regulator using a semiconductor I.C. fixed D.C.
voltage regulator.
FIG. 2 is a diagrammatic and schematic illustration showing the
adjustable voltage circuit of the present invention interconnected
with the same voltage regulator.
Referring to FIG. 1 the adjustable voltage regulator that is
heretofore known is indicated by the reference numeral 10 and is
connected between a source of direct current 11 and a load 12. The
source 11 is diagrammatically shown as being obtained by
rectification from an A.C. source to provide a positive voltage on
a lead 13 and a negative or ground potential on a lead 14. The load
12 is also diagrammatically shown as including an incandescent lamp
15 and a capacitor 16. It will be appreciated that insofar as the
circuit of the present invention is concerned that other and
different loads may be used and that similarly other sources of
direct current may be also employed.
The adjustable voltage regulator 10 includes an I.C. fixed D.C.
voltage regulator 17 having an input terminal 18, an output
terminal 19 and a common terminal 20 with such a regulator being of
the type illustrated previously and being basically an adjustable
current device. Connected to the output terminal 19 is a resistance
network consisting of a fixed resistance 21 and an adjustable
resistance 22 having a tap 23. A load 12, as shown, is connected to
the output terminal 19 and also to the ground lead 14 which is
effectively connected to the tap 23. A lead 24 connects the common
terminal 20 to a junction between the resistances 21 and 22.
It will be understood that as the tap 23 is moved along resistance
22 towards the resistor 21 that the output voltage to the load
approaches five volts while if the tap 23 is moved in reverse
direction and more resistance is inserted in the potential divider
the value of the output voltage increases.
Shown in FIG. 2 is the adjustable voltage regulator circuit of the
present invention, indicated by the reference numeral 25, and
connected to the D.C. source 11 and the load 12. The regulator
circuit 25 includes the fixed D.C. voltage regulator 17 having its
input terminal 18 connected to the plus side 13 of the source 11
and its output terminal 19 connected to the load 12. Its common
terminal 20 is also indicated with identical parts in the two
circuits bearing the same reference character. Connected between
the output terminal 19 and the ground 14 is a potential divider 26
that includes an adjustable resistance 27 having a tap 28, a
resistor 29 connected between the resistance 27 and the output
terminal 19 and a resistor 30 connected between the ground lead 14
and the resistance 27. Through two fixed resistors have been shown,
if desired, they may be incorporated into the resistance 27 to
increase the range of output voltage to the regulator.
Connected in parallel with the potential divider 26 across the
output terminal 19 and the ground lead 14 is a shunt path that
includes a resistor 31 connected between the output terminal 19 and
the emitter collector path of a transistor 32 with the path being
connected to the ground lead 14 through a resistance 33. A lead 34
connects the tap 28 to the base of the transistor 32. The common
terminal 20 is connected to the emitter of transistor 32.
In the operation of the prior art circuit shown in FIG. 1, the D.C.
source is selected to provide a voltage that is at least two volts
or so higher than the desired maximum output voltage. Assuming a
condition where it is desired to provide a maximum output voltage
that is variable in a range of from 5 to 571/2volts, the value of
the quiescent current which flows from the common terminal 20
through the resistance 22 to lead 14 amounts to perhaps 5
milliamps. The value of resistance 21 is selected at 300 ohms which
with 5 volts thereacross produces a current of 16 milliamps.
(called I21) as it flows through resistance 21. The variable
resistance 22 thus has a current flow of 16 and 5 or 21 milliamps.
which in order to produce a voltage drop of 521/2volts requires the
resistance 22 to have a maximum value of 21/2ohms. With these
values the maximum wattage of the resistor 22 is about 1.1
watts.
This circuit has the value of resistor 21 (300 ohms) selected such
that it is capable of permitting sufficient initializing current to
flow from the common to the output to start the regulator operating
(as it is basically a current gain device) even with an
incandescent lamp load 15. Any higher value of resistor 21 could
prevent sufficient initializing current from flowing. However, in
view of the current I21 being only about three times the quiescent
current, a change of even 1 milliamp. in the quiescent current is
capable of causing a change of 2 1/2volts in the output voltage and
this in many instances, has been found undesirable.
To overcome this defect caused by the change in the value of the
quiescent current, one typical approach is to make the current I21
have a value of about 10 times the quiescent current and in such an
instance I21 would be 50 milliamps. which is achieved by changing
the value of resistance 21 to 100 ohms. The current through the
variable resistance 22 will thus be 55 milliamps. (50 + 5) and the
value of the resistance 22 is about 1K ohms in order to produce a
55 volt drop thereacross. However, the power dissipated by this
amount of current through the variable resistance 22 closely
approaches 3 watts (55 milliamps. times 55 volts) and in many
instances has rendered such a circuit undesirable as too much heat
is produced, too costly a resistor 22 is required and too much
regulator output current is required.
In order to overcome the above defects the circuit of the present
invention has the resistor 31 equal approximately 300 ohms which is
of a sufficiently low value to enable starting of the regulator but
yet limits the current therethrough to 16 milliamps. The current to
the emitter of the transistor is thus 16 milliamps. plus 5
milliamps. quiescent current which assuming the transistor has a
current gain of 100 to 1 (a type 2N2907 for example) causes 0.21
milliamps. to flow through it from its emitter to the base and then
through the tap 28 to the ground 14. In order to minimize output
voltage changes caused by changes in the value of the quiescent
current, (which are reflected in a change of the current flowing to
the tap 28) the value of current from the output terminal 19
through the divider 26 is made to be 2.1 milliamps. (i.e. 10 times
0.21). As there is about a 4.5 voltage drop across the resistor 29
it may have a value of 2.15K ohms to produce this current.
In order to produce the output voltage range of 4.5 to 57 volts,
the drop across the variable resistor will be about 52 volts and
hence its value will be 23K ohms as 2.31 milliamps. of current is
flowing therethrough. The wattage loss in the resistor 27 is thus
52 volts .times. 2.31 milliamps. or only about 120 milliwatts.
The reason for there being a 4.5 volt drop across the resistance 29
is to provide a half volt voltage difference between the emitter
and base of transistor 32 such that it is caused to be fully
conducting as soon as the output voltage appears at the output
terminal 19. The value of resistor 33, which is basically a power
dissipating resistor and is used to decrease the voltage drop
across the transistor emitter base path and thus may, for example,
have a value which produces a 10 volt drop thereacross.
It will be seen from a consideration of the two circuits that the
prior art circuit is basically a constant current circuit and the
value of the output voltage is changed by varying the total
resistance in the potential divider 21. Thus, as the tap 23
approaches the resistor 21 the output voltage decreases while as it
approaches the ground 14 the output voltage is made to increase. On
the other hand, the present invention circuit is basically a
constant voltage circuit and the value of the current in the path
is made to change as the value of the resistance across the
constant voltage is changed. Thus, for the maximum output voltage,
the tap 28 is positioned on the resistance 27 at the junction with
the resistor 29 while for a minimum output voltage it is positioned
on resistor 27 toward the resistance 30 or the ground lead 14. In
both instances the value of the voltage between the tap 28 and the
output terminal 19 is 4.5 volts by reason of the transistor 32
being connected as in an emitter follower connection with the
emitter being maintained at 5 volts and the voltage at the tap
being approximately one-half a volt less due to the diode drop in
the transistor. Thus, the value of current flowing through the
potential divider is thus substantially changed in view of the
change in the resistance between the maximum and minimum positions
but still even with the maximum output voltage of perhaps around 57
volts, there is still only a small current flow in the potential
divider 26 and thus only very small power dissipation in the
variable resistance 27.
Accordingly, it will be understood there has been disclosed an
adjustable voltage regulating circuit which utilizes a fixed D.C.
voltage regulator of the integrated circuit type that normally
functions as a current gain device. The circuit utilizes only a
limited amount of output power and has low power dissipation by
reason of the use of a shunt path connected in parallel across a
potential divider with the output of the potential divider being
the output of the circuit. Thus, the shunt path enables sufficient
initializing current to flow to begin operation of the regulator
even with an incandescent lamp load while at the same time carrying
a substantial flow of current including the quiescent current to
the ground lead independently of the potential divider.
Variations and modifications may be made within the scope of the
claims and portions of the improvements may be used without
others.
* * * * *