US3581224A

US3581224A - Bipolar operational power supply

Info

Publication number: US3581224A
Application number: US796262A
Authority: US
Inventors: Sarkis Nercessian
Original assignee: Forbro Design Corp
Current assignee: Forbro Design Corp
Priority date: 1968-12-30
Filing date: 1968-12-30
Publication date: 1971-05-25
Anticipated expiration: 1988-05-25

Abstract

A bipolar operational power supply is constructed to provide stable operation over a wide range of gain settings including zero and with various load conditions in order to provide power output with AC or DC control or combinations of the two and in either voltage or current modes.

Description

United States Patent 72 1 Inventor Sarkis Nercossian [56] References Cited a Island UNITED STATES PATENTS [21] P 7963 2,281,238 4 1942 Greenwood 330 99 [22] Flled Dec. 30, 1968 2,860,195 1 H1958 Stanley 330/20X [45] Patented May 25, 1971 Assi nee Forbro n Co 3,010,087 11/1961 Ebbe et a1 330/20X 8 New York ,ff 3,058,068 10/1962 Hinrichs et al.. 330/1 10ux 3,092,783 6/1963 Krohn 330/118X 3,167,718 1/1965 Davis et a1. 330/110UX Primary Examiner-William H. Beha, Jr. 54 BIPOLAR OPERATIONAL POWER SUPPLY Barber 7 Claims, 7 Drawing Figs. I [52] US. Cl 330/99, ABSTRACT: A bipolar operational power supply is con- 323/19, 330/9, 330/ l 9, 330/81 structed to provide stable operation over a wide range of gain [51] Int. Cl H03! H34 settings including zero and with various load conditions in [50] Field of Search 330/99, 20, order to providepower output with AC or DC control or combinations of the two and in either voltage or current modes.

503 C51 16 1a 49 52 53 l PUSH-PULL POWER 6 AMPLIFIER 21 2s a e PATENIEUMAY S Ian SHEET 1 BF 5 M 503. E5| l8 49 PUSH-PULL POWER AMPLIFIER AMPLIFIER 4:

FIG

INVI'INTOR.

SARKIS NERCESSIAN lOO FIG 2 ATTORNEY PATENTED M25197:

SHEET 2 UF 5 PUSH-PULL POWER AMPLIFIER PUSH-PULL POWER AMPLIFIER INVENTOR. H6 4 SARKIS NERCESSIAN ATTORN EY PATENTED M2 19" 358 1 224 sum 3 OF 5 ff J-n/ Y 1 PUSH-PULL POWER AMPLIFIER k 9 INVENTOR.

SARKIS NERCESSIAN BY ATTORNEY PATENIEDHAY25|97| 3581.224

SHEET l 0F 5 4 VOLTAGE PUSH-PULL POWER as AMPLIFIER AMPLIFIER LOAD a4 20' I I P IF r55 PUSH-PULL. VOLTAGE POWER AMPL'F'ER AMPLIFIER u M W b a? FIG 6 INVENTOR.

SARKIS NERCESSIAN BY WWW ATTORNEY PATENTEUHAYZSIBYI 3.581.224

SHEET 5 0F 5 7 4 /38 VOLTAGE pusu-puu. AMPLIFIER POWER LOAD 6 AMPEFIER #l SLAVE 24 I la i )2 PUSH-PU POWER LOAD -59 AMPEIFIER *2 MASTER m 1 INVENTOR.

Fl 6 7 SARKIS NERCESSIAN ATTORNEY BIPOLAR OPERATIONAL POWER SUPPLY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention may be considered as belonging in cascaded amplifiers'with signal feedback.

2. Description of Prior Art Regulated power supplies have been built using control circuits which simulate a control bridge as described in U.S. Pat. No. 3,028,538. Such power supplies have been interconnected in a variety of series and parallel combinations as described in US. Pat. No. 3,275,927. These power supplies may be programmed in various ways generally providing unipolar output power. This one common characteristic, however, limits these prior art devices i.e. their basically unipolar nature. Because of this unipolar limitation the prior art power supply have been of very little use as bipolar devices.

SUMMARY In accordance with the present invention a high gain differential amplifier which is made unconditionally stable is combined with a unity voltage gain power amplifier to provide a power supply having novel gain-control capabilities. Two principal feedback paths are employed. One of these paths is an AC feedback path around the high gain amplifier and including integrating means and the other is a DC feedback path around the entire circuit from a power output point to the input of the high gain amplifier.

The power supply of the present invention is suitable as a source of bipolar DC power controlled as to voltage or current, and responsive to slewing rates to a predetermined frequency of several kilocyc'les, or as a hybrid device providing-AC with a DC offset. One of the more important results is that its output can be varied from maximum down to zero by means of the overall output control without causing instability in the system. Other advantages of the present invention will be apparent from the detailed description given in connection with various figuresof the Drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified circuit partly in block fon'n of one form of the present invention.

FIG. 2 is a graphical representation of the frequency response of the form of the invention shown in FIG. 1.

FIG.. 3 is a simplified circuit partly in block form of a modified form of the present invention.

FIG. 4 is a simplified circuit partly in block fonn of a further modified form of the present invention.

FIG. 5 is a simplified circuit partly in block form of a form of the present invention adapted to provide regulated current output.

FIG. 6 isa simplified circuit partly in block form of a form of the present invention adapted to combine two devices in accordance with the present invention and supplying a common load.

FIG. 7 is similar to FIG. 6 except the circuit is adapted to supply power to two independent loads,

FIG. I is a simplified schematic circuit diagram, partly in block form, of one form of the present invention. Voltage amplifier 1 includes input terminal 2, common terminal 3 and output terminal 4. Amplifier 1 is bipolar i.e. it accepts positive and negative input voltages or currents and provides bipolar output voltages. Following amplifier 1, unity voltage gain push-pull power'ampiifier 5 is provided with input terminal 6 and

output terminals

7 and 8 in turn connected to load terminals l0 and 11 respectively across which is connected load 9. An input control signal 12 is connected between common terminal 3 over lead 13 and input terminal 2 through input resistor l4 and resistor 47. Two feedback control circuits are provided, one across voltage amplifier 1 in the form of an AC path provided by one of

capacitors

15 and 16 selected by switch 17-18-19 connected from output 4 to input 2, and the other a DC path across the entire circuit from the output of push-pull power amplifier 5 to input of voltage amplifier 1 through resistor 47 in the form of variable output control resistor 20 connected from load terminal 10 to input terminal 2. Both the AC and DC feedback paths must be degenerative. This is the case when amplifier 1 inverts between input terminal 2 and output terminal 4 and amplifier 5 does not invert. The DC feedback path comprises a variable resistor and serves to control the output voltage. The AC feedback path through either of

capacitors

15 or 16 may be selected by switch 17-18-19 and acting with resistor 47 connected between input terminal 2 and null junction 48 serves to determine the roll-off characteristics of amplifier 1 and furthermore of the entire amplifier since power amplifier 5 is chosen to be flat beyond any chosen unity gain frequency. The selection of the AC feedback impedance, while generally made in view of the nature of the load impedance, is quite independent thereof. A lower impedance in this feedback path results in greater tolerance in output voltage or shunt capacitance while maintaining unconditional stability while a higher impedance provides higher slewing rate capability. Checking and/or calibration of the power supply may be accomplished by connecting a voltage determined by the position of variable contact 21 on potentiometer 21-22 connected between

voltage sources

23 and 24 by means of switch 25-26 through input resistor 27 to input terminal 2. These voltage sources may also be used as sources of input current to program the output of the power supply.

The frequency response of amplifier 1 as determined by one of capacitors I5 and 16 and resistor 47 will have a falling characteristic, falling at the rate of 20 db. per octave, meeting the criteria for stability, and will have a unity gain frequency at the frequency where the reactance of the capacitance (15 or 16) equals the resistance of the resistor 47. Since amplifier 5 is chosen to be essentially flat unity voltage gain at least to the chosen unity gain frequency, the overall response from input terminal 48 tooutput terminal 10 will be determined by the chosen response of amplifier -I. This mode of operation permits the connection to any type of load, resistive, inductive or capacitive without affecting the stability of the power supply. Particularly important in a power supply is the ability to vary the output voltage by varying the value of the voltage control resistor 20 without affecting the response or stability of the system. The circuit of the present invention as shown here in FIG. 1 provides stable operation as resistor 20 is varied down even to zero, providing zero output.

FIG. 1 also shows a safety means for preventing over-driving the output voltage. This circuit is particularly significant due to the fact that amplifiers I and 5 may be operated from different bias voltage sources and when heavy current is being drawn from amplified 5, the associated bias voltages may drop while those supplying amplifier 1 will be at full voltage. Under such conditions amplifier 1 may drive amplifier 5 into saturation. The two back-to-back Zener diodes 49-50 and 51-52 are connected over leads 53 and 54 between output point 4 of amplifier 1 to null junction48. Any tendency for the voltage at output 4 to exceed the Zener voltages in either direction will cause heavy feedback current to flow preventing any further rise of voltage.

FIG. 2 is a graphical representation in terms of frequency response of one possible effect of switching between

capacitors

15 and 16 of FIG. I substantially unaffected by the output voltage or current as determined by the particular value of output control resistor 20. Curve A is a typical frequency response of amplifier l. for the lower capacitance value of capacitances l5 and 16 while curve B is typical for the higher value. For example, the 400 kHz. unity gain point may be provided with capacitor 16 equal to I00 pf. and resistor 47 equal to 4 k. ohms, since the reactance of I00 pf. is 4 k. at 400 kHz. Increasing the capacitance 10 times to 1000 pt. will provide the 40 kHz. unity gain point.

FIG. 3 is a simplified schematic circuit diagram partly in block form of a modified form of the present invention. The same numbers as those used in FIG. 1 are used to designate corresponding circuit components. In FIG. 3 a circuit is shown for providing simultaneous AC and DC power output or, stating it another way, an AC output superimposed on a DC output. In this case a DC programming voltage supplied as from potentiometer 2l-22 is applied through closed contacts 25-26 and

resistors

27 and 47 to input 2 and in parallel an AC input from AC source 12 through resistor 14 to null junction 48. The actual output voltage components will be equal to the voltages of

sources

12 and 21 multiplied by the ratio of the resistances of

resistors

20 and 14 for

source

12 and 20 and 27 for source 21.

FIG. 4 is a simplified schematic circuit diagram partly in block form of a further modified form of the present invention. In this form of the invention both AC (from 12) and DC (from 21-22) are applied to input terminal 2 through resistor 47. However, in this case the output across load 9 is controlled by a remote output control resistor 28 connected between load terminal 10 and input terminal 2 over a remote line shielded cable shielded by grounded shield 29. Otherwise the operation is similar to that of FIG. 3 described above.

FIG. is a simplified schematic circuit diagram partly in block form for providing a regulated output current to the load. In this form of the invention the output control resistor 28 is connected from junction point 30 to input terminal 2. A

. current sensing resistor 29 is connected in series with load resistor 9 so that output current from amplifier 5 flowing in load resistor 9 also flows through resistor 29. The voltage drop in resistor 29 due to this output current supplies the voltage applied through resistor 28 back to input 2. The voltage across load 9 is thus current regulated rather than voltage regulated as in FIGS. 1, 3 and 4.

FIG. 6 is a simplified schematic circuit diagram partly in block form of a form of the present invention in which two of the bipolar power supplies as described above are connected to cooperate in supplying a common load. The numerical designations are the same for parts corresponding with parts as described above and in the second power supply corresponding parts are designated by the same numbers primed. The upper power supply is provided with a programming voltage from adjustable contact 21 of potentiometer 21-22 bridged across

voltage sources

23 and 24. The reference resistor is 27 and the output voltage control is variable resistor 20 connected between load terminal 32 and input terminal 2 over lead 33. Similarly, the second power supply is provided with programming voltage from adjustable contact 21' of potentiometer 21 '-22' bridged across voltage sources 23' and.

24'. The reference resistor is 27' and the output voltage control is variable resistor 20' connected between output terminal 7' and input terminal 2' over lead 36. The load 31 is connected between

terminals

32 and 34 and the two power supply output tenninals 11 and l0'11' are connected in series across these load tenninals so that the sum of the output voltages of the two power supplies are applied across the load, The voltage control feedback circuit connected over lead 33 to load terminal 32 and the return circuit over leads 35-37 connected to load terminal 34 provides for remote sensing of the load voltage so that any voltage drops in leads between power supply output terminals 10 and 11 and

load terminals

32 and 35 respectively are outside the voltage control circuit and the actual lo'ad voltage is regulated unaffected by the lead drops. It will be seen that the two power supplies will contribute equally to the load voltage if the two input voltages, reference resistors and voltage control resistors are made equal and will contribute unequally otherwise.

FIG. 7 is a simplified schematic circuit diagram partly in block form of a form of the invention similar to that of FIG. 6 in that two power supplies are involved but differing in that separate loads are powered. In FIG. 7 the lower power supply is programmed by potentiometer output 21 and supplies power to load 39 while the upper power supply is programmed by the output voltage of the lower power supply over leads 45 and 46 through input resistor 44. Since the power supply output volta es are inverted from the ingut voltages the output etween ermmals 7 and 8' 1s mverte as it IS app red to mput 2. This inversion is accomplished by connecting terminal 7 to terminal 8 and deriving the input for the upper power supply from terminal 8'.

Iclaim:

1. In a bipolar output regulated power supply, the combination of: 1

an operational voltage amplifier including an inverting input terminal, an output terminal and a common terminal;

. a push-pull, unity voltage gain, power amplifier coupled to said operational voltage amplifier output terminal and including an input terminal and two output terminals, one in phase and the other out of phase with the last said input tenninal;

a null junction terminal;

resistive means connected between said null junction and said inverting input to the voltage amplifier;

resistive degenerative feedback'means connected between said in phase output and said null junction;

capacitive degenerative feedback means connected between said output of the voltage amplifier and said inverting input thereof;

and a source of input voltage connected through a resistive means between said common terminal of the voltage amplifier and said null junction; whereby the unity gain frequency of said voltage amplifier is substantially determined by the capacity of said capacitive means and the resistance of said first said resistive means. V

2. A bipolar output regulated power supply as set forth in claim 1; I

wherein said resistive feedback means is a variable resistor for controlling the output of said power supply.

3. A bipolar output regulated power supply as set forth in claim 1;

and including two back-to-back series connected Zener diodes connected between said in phase output of said power amplifier and said null junction for limiting the output voltage of said power amplifier in both the positive and negative direction.

4. A bipolar output regulated power supply as set forth in claim 1;

and including means for applying known voltages, both positive and negative, through resistive means, between said common terminal of said voltage amplifier and said null junction, for activating said power supply in a known mode.

5. A bipolar output regulated power supply as set forth in claim 1; and including a source of known DC current connected between said common terminal and said null junction and wherein said source of input voltage is a source of alternating current.

6. A bipolar output regulated power supply as set forth in claim 1; wherein said capacitive feedback means is plural and including switch means for selecting one of said capacitive means to be active connected between said output of said voltage amplifier and said inverting input thereof.

7. A bipolar output regulated power supply as set forth in claim 1; wherein said power amplifier has a frequency response which is substantially fiat to and beyond said unity gain frequency of said power amplifier.

Claims

1. In a bipolar output regulated power supply, the combination of: an operational voltage amplifier including an inverting input terminal, an output terminal and a common terminal; a push-pull, unity voltage gain, power amplifier coupled to said operational voltage amplifier output terminal and including an input terminal and two output terminals, one in phase and the other out of phase with the last said input terminal; a null junction terminal; resistive means connected between said null junction and said inverting input to the voltage amplifier; resistive degenerative feedback means connected between said in phase output and said null junction; capacitive degenerative feedback means connected between said output of the voltage amplifier and said inverting input thereof; and a source of input voltage connected through a resistive means between said common terminal of the voltage amplifier and said null junction; whereby the unity gain frequency of said voltage amplifier is substantially determined by the capacity of said capacitive means and the resistance of said first said resistive means.

2. A bipolar output regulated power supply as set forth in claim 1; wherein said resistive feedback means is a variable resistor for controlling the output of said power supply.

3. A bipolar output regulated power supply as set forth in claim 1; and including two back-to-back series connected Zener diodes connected between said in phase output of said power amplifier and said null junction for limiting the output voltage of said power amplifier in both the positive and negative direction.

4. A bipolar output regulated power supply as set forth in claim 1; and including means for applying known voltages, both positive and negative, through resistive means, between said common terminal of said voltage amplifier and said null junction, for activating said power supply in a known mode.

7. A bipolar output regulated power supply as set forth in claim 1; wherein said power amplifier has a frequency response which is substantially flat to and beyond said unity gain frequency of said power amplifier.