US3310727A

US3310727A - D.c. to d.c. voltage converter with undervoltage-responsive, mode selector means

Info

Publication number: US3310727A
Application number: US311844A
Authority: US
Inventors: John B Flannery
Original assignee: Ovitron Corp
Current assignee: Ovitron Corp
Priority date: 1963-09-26
Filing date: 1963-09-26
Publication date: 1967-03-21
Anticipated expiration: 1984-03-21

Description

March 21, 1967 J. B. FLANNERY I 3,310,727

D.C. T0 D.G. VOLTAGE CONVERTER WITH UNDERVOL'IAGE-RESPONSIVE, MODE SELECTOR MEANS Filed Sept. 26, 1963 55 "I I I I I 34 l I I OL/fP/f 3 #6 I I I ma I wPuf/MK) I 705- I I I 65 I I I I I I I I I L J I NVEN TOR. (fay/v.5. fZ/l/V/VEFX United States Patent ice D.C. T0 D.C. VOLTAGE CONVERTER WITH UNDERVGLTAGE-RESPONSIVE, MODE SE- LECTOR MEANS John B. Flannery, Chelmsford, Mass, assignor to Ovitron Corporation, Newburgh, N.Y., a corporation of Delaware Filed Sept. 26, 1963,. Ser. No. 311,844 5 Claims. (Cl. 321-14) This invention relates to a voltage converter and more particularly to a converter which utilizes transistors to convert a DC potential from one level to another.

Diesel locomotives have come into wide use in recent years. In order to start these locomotive engines, a DC. battery source is employed and for various important design reasons relating the starting equipment, a battery voltage of 74 volts has been Widely used. However, certain track safety equipment has for some time been standardized for operation at 32 volts DC. and it is therefore necessary to convert from the .D.C. voltage of 74 volts to a DC. voltage of 32 volts. In the prior art this has been accomplished by a motor-generator set. The motor-generator set, however, is relatively expensive and must be reconditioned or rebuilt about once a year at a substantial cost to from 30 to 40% of the original cost of the unit.

Accordingly, it is an object of this invention to make available apparatues for converting a DC. potential from one value to another which is less expensive than an equivalent motor-generator set for producing the same output power. I

It is another object of the invention to provide apparatus for converting a DC. voltage of given value to a value approximately half of that value.

A further object of the invention is to eliminate the high maintenance cost required by motor-generator sets presently employed on modern diesel locomotives.

One of the features of the invention lies in the provision of a mode selector for providing a voltage at a pair of output terminals by automatically connecting the terminals either directly to the input voltage when it is at a predetermined reduced value or to the reduced output voltage of the converter circuit.

Another feature of the invention lies in the provision of voltage regulator means for maintaining the voltage output of the regulator within predetermined limits.

All of the objects, features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing which shows a schematic diagram of a converter circuit in accordance with the invention.

In the drawing, which shows an arrangement particularly suitable for use with diesel locomotives, there is provided a pair of input terminals a and 10b for receiving an input voltage of 74 volts, and a pair of output terminals 11a and 11b for providing an output voltage normally having a value of approximately 32 volts. A transformer 12 is employed to aid in providing the volt-age conversion, this transformer having three similar

primary windings

13, 13' and 13", and a secondary winding 14. Each of the transformer

primary windings

13, 13' and 13" forms part of a more or less independent circuit, indicated as bank 1, bank 2 and bank 3, each bank being shown separately within a dashed line rectangle.

In bank 1 there is provided two transistors 17 and 18 which may be either NPN or PNP type, PNP type being shown in the drawing. The

collector electrodes

22 and 25, respectively, of these transistors 17 and 18 are con-' 3,310,727 Patented Mar. 21, 1967 nected to a wire 26 for receiving a collector operating potential which is more negative than the positive potential on the input terminal 1%. The

emitters

20 and 23 of the transistors 17 and 18 are connected, respectively, to the terminals 13b and 13d of the transformer primary winding 13. The portion of the winding 13 between the terminals 13b and 13d is center tapped at the terminal 13c, this latter terminal being connected to the positive input terminal 10b. The

base electrodes

21 and 24 of the transistors 17 and 18 are connected, respectively, to the primary terminals 13a and 13e through

biasing resistors

27 and 28. The portion of the winding 13 between the terminals 13a and 13b and the portion between the

terminals

13d and 13e comprise biasing windings for the transistors to which they are connected. The transistor 17 in bank 1 is the starting transistor, as between two transistors 17 and 18, and is therefore provided with a starting resistor 29 connected between the base and

coilector electrodes

21 and 22.

The circuitry and components in each of the

banks

2 and 3 are identical to that of bank 1. These additional banks are provided to increase the power output to three times that which can be provided by only one bank. In

banks

2 and 3, like components as those in bank 1 are designated, respectively, with a prime and double prime designation following the numeral.

The circuits of each of the banks also include a circuit to protect the transistors therein against damage due to transient voltages, such as spike potentials which are developed in the voltage input circuit at various times during operation of the diesel engine. These protection circuits include Zener

diodes

30, 30' and 30" which are connected between the positive and negative potential supply points for the particular bank; thus, for bank 1 the diode is connected between the wire 26 and the positive input terminal 10b. Each

diode

30, 30 and 30' has a breakdown potential sufficient to cause conduction at a predetermined level, so that no transient potential above this level can reach the transistors in the different banks to cause damage thereto. breakdown level will depend to some extent upon the particular transistors employed. The

diodes

30, 30 and 30" are preferably, though not necessarily bridged by

resistors

31, 31' and 31", each having a value, such as for example, 10,000 ohms.

Resistors

34 and 35, through which operating potential is supplied to the various banks from the negative input terminal 10a, also comprise a part of the transistor protection circuit. The over-all resistance of these

resistors

34 and 35 is chosen to match the dynamic impedance of the Zener

diodes

30, 30 and 30". These diodes and the

resistors

34 and 35 cooperate with one another to provide full protection for the transistors in the three banks against the transient voltages referred to above.

, The circuits within each of the

banks

1, 2 and 3 function much in the same manner as a flip-flop circuit, well known in the art. Considering only bank 1 for purposes of explanation, when operating potential is applied thereto, the transistor 17 is caused to conduct, however, this transistor soon becomes saturated, causing it to become non-conductive and the transistor 18 to become conductive. The transistor 18 in like manner then becomes saturated causing it to become non-conductive, at which time the transistor 17 again becomes conductive. This process continues so long as operating potential is applied. Due to this on-off switching action of the transistors 17 and 18, a pulsating DC current passes through the primary winding 13 causing an AC. potential to be developed in the secondary winding 14. The banks 2 and 3 'function in the same manner and simultaneously with bank 1 to increase the power available from the winding 14.

This particular predetermined The A.C. developed in the secondary winding 14 is rectified by a conventional full wave rectifier circuit 36, providing a DC. voltage at the output terminals 37a and 37b thereof. The rectifier output terminal 37 b is connected to the positive converter output terminal 11b through a wire 38, a contact 39 and armature 49 of a relay 41, and a wire 42. The rectifier output terminal 37a is connected to the negative converter output terminal 11a through a wire 43 into a voltage regulator 44, out of the voltage regulator via wire 45, through a contact 46 and arm 47 of the relay 41, and a wire 43.

The voltage regulator 44 includes a pair of transistors 49 and 50 of the PNP type connected in parallel with one another. These two transistors are connected in series between the rectifier output terminal 37a and the negative converter output terminal 11a when the relay arm 47 is in electrical contact with the contact point 46. These two transistors 49 and 50 are controlled by a PNP type transistor 51 and an NPN type transistor 52 cooperating therewith. The emitter 53 of the transistor 51 is connected to the arm of an adjustable resistor 59 which may be varied to set the voltage level at the converter output terminals 11a and 11b. This adjustable resistor 59 is connected between the output terminals 11a and 11b when the relay 41 is in the energized position shown in the drawing, and functions as a voltage change sensing resistor in the voltage regulator 44, as will be seen. The base 54 of the transistor 51 is connected to the junction point between a resistor 60 and a Zener diode 61, these being connected in series between the rectifier output terminals 37a and 37b. The collector 55 of the transistor 51 is connected to a collector load resistor 62. This load resistor 62 is connected in series with a resistor 63, the latter being-connected between the emitter 56 and base 57 of the transistor 52. The resistors 62 and 63 are connected in series with a resistor 64 to the negative rectifier output terminal 37a. The collector 58 of the transistor 52 is connected to a collector load resistor 65; it is also connected to the

base electrodes

66 and 67 of the transistors 49 and 50 through

resistors

68 and 69, respectively.

When a change tends to occur in the value of the voltage at the converter output terminals 11a and 115, the voltage at the arm of the adjustable resistor 59 will also change, since this resistor is connected across these terminals, causing the bias on the transistor 51 to change. This in turn causes a change in the conduction of the transistor 51, resulting in a change in the voltage drop across the resistors 62 and 63. This in turn changes the bias on the transistor 52, altering its conduction and thus also the value of the IR drop across the collector load resistor 65. This IR drop change is reflected in a change of the bias on the

base electrodes

66 and 67 of the transistors 49 and 50, respectively, producing a change in conduction in these transistors. The direction of this change is such as to oppose the change in the voltage at the output terminals 11a and 11b which caused it. Thus, when the voltage across the output terminals 11a and 11]; tends to either increase or decrease, the circuit of the voltage regulator 44, which is essentially a negative feedback loop, will maintain this output voltage at a constant level of approximately 32 volts.

As noted above, the converter circuit of this invention is designed especially for use with diesel locomotives, and during normal operation the voltage regulator 44 will maintain the output voltage at approximately 32 volts. However, when the diesel must be started, either initially or after stalling, the input voltage at the terminals a and 10b drops from a value of 74 volts to approximately 35 volts. This causes the output voltage at the terminals 11a and 11b to drop to a value of about volts, which is insufficient to operate the safety equipment to which it must supply power. This invention, therefore, includes a mode selector for automatically disconnecting the voltage regulator 44 during the period when the diesel is being started and connecting the output terminals 11a and 11b directly to the input treminals 10a and ltlb. This mode selector comprises the relay 41 in which the coil 71 is connected in series with a Zener diode 72 across the input terminals 10a and 10b. This Zener diode is selected to have a characteristic such that it is conductive only at values slightly greater than the 35 volt value to which the input potential of 74 volts will drop when the diesel is being started. At this lower value of 35 volts therefore, the relay will drop open so that the armatures 40 and 47 are in the position shown by the dashed lines, in contact with contact points 73 and '75. In this unenergized position the output terminals 11a and 11b are directly connected through the contacts 73 and to the input terminals 10a and 10b. Thus, the voltage of 35 volts, a value less than 10% over the desired value of 32 volts, will be available to operate the track safety equipment during starting of the diesel engine. When the diesel has been started the heavy load on the starting battery no longer exists and the input voltage therefore will return to a value of 74 volts. The Zener diode 72 will therefore become conductive, energizing the relay 41 to connect the output terminals 11a and 11b to the output of the con verter through the relay contacts 39 and 46.

The utilization of the device described herein allows significant savings both in terms of initial cost and main tenance. More specifically, the motor-generator sets of type referred to above cost approximately $450. The apparatus described according to the invention herein provides the electrical output necessary to operate the track safety equipment at a cost of only 45 to 55% of the cost of the motor-generator. Additionally, the motorgenerator set requires major overhauls approximately every year and this costs approximately 30 to 40% of the cost of a new motor-generator set. By sharp contrast the converter system described herein requires no such periodic overhaul and may operate for years without causing even minor technical difficulties. Furthermore, the converter device has an indefinite life, which is not true of the motor-generator set, since the bearings and commutators are subject to continuous wear.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1; A power supply conversion system comprising a pair of input terminals for receiving a DC. input potential having a given value,

a transformer,

a semiconductor switching circuit including a plurality of transistors connected to said input treminals for delivering a pulsating current to the primary Winding of said transformer, whereby an A.C. potential is induced in the secondary winding of said transformer,

means connected to said transformer secondary for rectifying said A.C. potential,

voltage regulator means connected to said rectifier means for maintaining the level of said rectified potential Within predetermined limits,

a pair of output terminals,

and mode selector means connected to said output terminals, to said regulator means and to said input terminals, said mode selector means being operable to connect said output terminals to the output from said regulator when said input potential is at approximately said given value, and to connect said output terminals directly to said input terminals when the input potential drops to a predetermined value below said given value.

2. The invention described in claim 1 wherein said mode selector means includes an electromagnetically actuated switch and a diode, said diode being connected in series with the coil of said switch across said input terminals, said diode further being non-conductive below said potential of given value and conductive above said potential of given value.

3. The invention described in claim 1 which further includes voltage protection means connected to said transistors to protect said transistors from the damaging effects of transient spike potentials above a predetermined value originating in the circuit connected to said input terminals, said voltage protection means including a diode connected in series with means for matching the dynamic impedance of said diode.

4. A power supply conversion system comprising a pair of input terminals for receiving a DC. input potential having a given value,

a circuit responsive to transient spike potentials connected between said input terminals, said circuit including a Zener diode in series with a. resistor for matching the dynamic impedance of said diode,

a transformer,

a semiconductor switching circuit including a plurality of transistors connected across said diode for delivering a pulsating current to the primary winding of said transformer, whereby an AC. potential is induced in the secondary winding of said transformer,

a pair of output terminals,

and mode selector means connected to said output terminals, to said regulator means and to said input termnials, said mode selector means being operable to connect said output terminals to the output from said regulator when said input potential is at approximately said given value, and to connect said output terminals directly to said input terminals when the input potential drops to a predetermined value below said given value.

5. A power supply conversion system comprising a pair of input terminal for receiving a D.C. input potential having a given value,

a transformer,

a semiconductor switching circuit including a plurality of transistors connected to said input terminals for delivering a pulsating current to the primary winding of said transformer, whereby an AC. potential is induced in the secondary winding of said transformer,

voltage protection means connected to said input terminals and to said transistors to protect said transistors from the damaging effects of transient spike potentials above a predetermined value, said voltage protection means including a diode in series with means for matching the dynamic impedance of said diode,

a pair of output terminals,

and mode selector means, said mode selector means including a current actuated switch having a coil connected in series with a diode across said input terminals, said switch being connected to said output terminals, to said regulator means and to said input terminals, said mode selector means being operable to connect said output terminals to the output from said regulator when said input potential is at approximately said given value, and to connect said output terminals directly to said input terminals when the input potential drops to a predetermined value below said given value.

References Cited by the Examiner UNITED STATES PATENTS 1/1966 Gilbert et a1 321-11 JOHN F. COUCH, Primary Examiner.

W. H. BEHA, Assistant Examiner.

Claims

1. A POWER SUPPLY CONVERSION SYSTEM COMPRISING A PAIR OF INPUT TERMINALS FOR RECEIVING A D.C. INPUT POTENTIAL HAVING A GIVEN VALUE, A TRANSFORMER, A SEMICONDUCTOR SWITCHING CIRCUIT INCLUDING A PLURALITY OF TRANSISTORS CONNECTED TO SAID INPUT TERMINALS FOR DELIVERING A PULSATING CURRENT TO THE PRIMARY WINDING OF SAID TRANSFORMER, WHEREBY AN A.C. POTENTIAL IS INDUCED IN THE SECONDARY WINDING OF SAID TRANSFORMER, MEANS CONNECTED TO SAID TRANSFORMER SECONDARY FOR RECTIFYING SAID A.C. POTENTIAL, VOLTAGE REGULATOR MEANS CONNECTED TO SAID RECTIFIER MEANS FOR MAINTAINING THE LEVEL OF SAID RECTIFIED POTENTIAL WITHIN PREDETERMINED LIMITS, A PAIR OF OUTPUT TERMINALS,