GB2265028A - Generating constant ac voltage or current - Google Patents

Generating constant ac voltage or current Download PDF

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Publication number
GB2265028A
GB2265028A GB9205070A GB9205070A GB2265028A GB 2265028 A GB2265028 A GB 2265028A GB 9205070 A GB9205070 A GB 9205070A GB 9205070 A GB9205070 A GB 9205070A GB 2265028 A GB2265028 A GB 2265028A
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United Kingdom
Prior art keywords
voltage
current
output
loop
output voltage
Prior art date
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Granted
Application number
GB9205070A
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GB2265028B (en
GB9205070D0 (en
Inventor
Desmond Wheable
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Individual
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Individual
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Publication date
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Priority to GB9205070A priority Critical patent/GB2265028B/en
Publication of GB9205070D0 publication Critical patent/GB9205070D0/en
Publication of GB2265028A publication Critical patent/GB2265028A/en
Application granted granted Critical
Publication of GB2265028B publication Critical patent/GB2265028B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M5/25—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
    • H02M5/257—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M5/2573—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Voltage And Current In General (AREA)

Abstract

A regulated voltage or current is produced at a load RL by controlling a triac TR1 using an opto-isolator LED1, R1. Sensed current or voltage is compared with a zener voltage Z1 in an operational amplifier circuit in order to vary the resistance of light sensitive resister R1 so as to adjust the firing angle of triac TR1 and thereby regulate the output of transformer T1. The circuit may be used in earth loop bonding resistance testing, or as a pre-regulator in a DC power supply. <IMAGE>

Description

A NOVEL METHOD OF GENERATING CONSTANT ALTERNATING, VOLTAGE OR CURRENT SUPPLY When making a circuit to deliver AC current from the secondary of a mains transformer into a load the control of this current is not easy,in fact when it is required to deliver a high current into a low resistance load such as required when testing the integrity of earth bonding it is normal to drive the required current which can be selected to a value of up to 25 AMPS into a resistive load of 0.1 OHMS ,the nominal pass resistance,for other load resistance values the current will vary,it will go up for lower values of resistance which could cause damage and will go down for higher resistance loads which means the test is not being carried out at the correct current.
The object of this patent application is a method of generating an AC constant current or voltage.The circuit will maintain the set current or voltage over a wide range of resitive loads.Fig 1 shows the proposed circuit,it is well known that by altering the phase angle that a triacs is fired during a mains cycle it will alter the effective voltage applied to the load,this is usually achieved by altering the value of R1 which coupled with C1 determines the phase angle at which the Triac is fired via the Diac Dl.The lower the value of R1 the smaller will be the phase angle to firing Trl and the higher will be the voltage applied to the load and, of course, the converse applies.Now in order to provide a control loop to control the output current it will be necessary control the value of R1 and at the same time provide isolation between the primary and the secondary load. In order to provide the isolation and control of R1 it is proposed to use a photo sensitive resistance such as a Cadmium sulphide type (NORP) the resistance of this component is controlled by a variable light emitter such as a light emitting diode both items enclosed in a light tight container as shown in Fig 2.Explaining the control circuit in Fig 1 the secondary of transformer T 1 is loaded by two resistors in series RL is the load RF is the reference resistance and the circuit maintains a constant voltage across it,R3,Dl,R4,C3 & operational amplifier Al forms a precision rectifier,thus a DC voltage is developed across C3 which is directly proportional to the AC voltage across RF.The DC voltage across C3 is amplified by A3 R5 & R7,this voltage is compared with the set point voltage generated by zenner diode Z1 and adjusted by the potentiometer chain RV1 & R7.Operational amplifier A4 R8 & R9 form a gain controlled comparator.
If the output from A2 is lower than the the set point voltage output from A3 and hence the AC voltage across RFis lower than the loop is calling for,this will cause the output of A4 to rise which in turn increases the voltage applied to LED1, the increased light output from LED1 will cause the light sensitive resistor R1 to decrease in value, this as stated earlier will cause the applied voltage to the transformer to increase and thus increase the voltage across RF.From the above it can be seen that a feed back loop around a transformer is possible without degrading primary to secondary isolation.Also if the voltage RF is maintianed constant depending on the set point voltage ,then the current through RL will be constant.Also if the circuit is modified as shown in fig.3 then it will control the AC voltage output from the secondary of transformer Tl,it will provide a contant voltage across the load RL in the same way as in the constant current case, formally described,a constant voltage was developed across RF. The voltage will be independent of load resistance and variation of primary input voltage dependant only, in common with all loop control systems, on the loop gain.
Fig 4 shows a simplified version were the feed back control loop is removed and the AC load current is set by either R1 or R2 selected by switch SW1.A DC output which is directly proportion to the AC load current is provided at the output of A2.

Claims (1)

  1. Claim 1 Is a method of generating a constant alternating current source using combination of an opto isolator made up of light source and a light sensitive resistor a current sensing resistor and an operational amplifier,connected as a precision rectifier,the output of which is compared against a reference voltage in a feed back loop which in turn alters the firing angle of a triac connected in series with the primary of a mains transformer whose output controls the current.The optoisolator is the novel method of providing isolation from the mains in the current control loop which is a necessary safety requirement in any instrumentation.
    Claim 2 As claim 1 but instead of using a current sensing resistor the output voltage is sensed and the loop controls the output voltage providing a constant output voltage referred to a reference voltage.
    Claim 3 The opto isolator used is not currently available as a component and is a novel method of brining two well known components,a light source such as an LED and a light sensitive resistor, together to make opto isolated component for use in claims one and two.
GB9205070A 1992-03-09 1992-03-09 A novel method of generating constant alternating voltage or current supply Expired - Fee Related GB2265028B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9205070A GB2265028B (en) 1992-03-09 1992-03-09 A novel method of generating constant alternating voltage or current supply

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9205070A GB2265028B (en) 1992-03-09 1992-03-09 A novel method of generating constant alternating voltage or current supply

Publications (3)

Publication Number Publication Date
GB9205070D0 GB9205070D0 (en) 1992-04-22
GB2265028A true GB2265028A (en) 1993-09-15
GB2265028B GB2265028B (en) 1996-05-01

Family

ID=10711749

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9205070A Expired - Fee Related GB2265028B (en) 1992-03-09 1992-03-09 A novel method of generating constant alternating voltage or current supply

Country Status (1)

Country Link
GB (1) GB2265028B (en)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2003628A (en) * 1977-09-05 1979-03-14 Solartron Electronic Group Voltage control systems
GB1542636A (en) * 1976-12-08 1979-03-21 Marinair Ltd Dc-ac inverters
GB2031623A (en) * 1978-09-29 1980-04-23 Siemens Ag Power supplies
GB2168865A (en) * 1984-12-20 1986-06-25 Stanley Electric Co Ltd Switching power supplies
US4680827A (en) * 1985-09-28 1987-07-21 Interlava Ag Vacuum cleaner

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1542636A (en) * 1976-12-08 1979-03-21 Marinair Ltd Dc-ac inverters
GB2003628A (en) * 1977-09-05 1979-03-14 Solartron Electronic Group Voltage control systems
GB2031623A (en) * 1978-09-29 1980-04-23 Siemens Ag Power supplies
GB2168865A (en) * 1984-12-20 1986-06-25 Stanley Electric Co Ltd Switching power supplies
US4680827A (en) * 1985-09-28 1987-07-21 Interlava Ag Vacuum cleaner

Also Published As

Publication number Publication date
GB2265028B (en) 1996-05-01
GB9205070D0 (en) 1992-04-22

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Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19970309