MXPA97008466A - Activation circuit of silicon controlled rectifier for high volt control applications - Google Patents

Abstract

The present invention relates to a silicon controlled rectifier (SCR) drive circuit comprising a diode, a capacitor and a silicon controlled rectifier (SCR) wherein the diode charges the capacitor to drive the controlled silicon rectifier. There is also provided a silicon controlled rectifier (SCR) driving circuit comprising a first and second diode, a first and a second capacitor and a controlled silicon rectifier (SCR) wherein the first diode charges the first capacitor to drive the rectifier Silicon controlled (SCR) when one line voltage is positive and the second diode charges the second capacitor to drive the silicon controlled rectifier (SCR) when the line voltage is negative. An insulating circuit comprising at least three optocouplers placed in series is also provided where the optocouplers isolate a low control voltage of an energy voltage at

Description

ACTIVATION CIRCUIT OF CONTROLLED RECTIFIERS OF SILICON FOR HIGH VOLTAGE CONTROL APPLICATIONS Background of the Invention 1 Field of the Invention This invention relates to activation circuits and more particularly to an SCR activation circuit that is useful in industrial control applications 2 Description of the Related Art Activation circuits that employ controlled silicon rectifiers or SCR's are used for power equipment or other loads such as variable frequency or electromagnetic feeders. Typically, a microcontroller is used to send a suitable signal to an SCR to feed the load.

The SCR's are turned on to their conductive state by applying a drive impulse to their gate connection at some point during a half cycle of the power source line frequency. When activated, the SCR continues to drive until the current passing through of this falls below its retentive current value By delaying the point in time relative to the applied half-wave the device is operated, the average energy applied to a connected load can be changed for control purposes. Several schemes have been devised and used to drive the SCR's, although different from those that directly connect the gate to the anode, in which case the SCR becomes only a diode, there is always some delay from the zero crossing point in the form of voltage wave applied to the point where the SCR is turned on depending on the circuit used, so it is not possible to obtain the maximum energy available from the source. It can be difficult to operate the SCR close enough to the zero crossing of the voltage waveform due to the time required to have enough available power to drive the SCR. Therefore, it is desirable to have an SCR drive circuit closer to the zero crossing point of the voltage waveform. It is also desirable to electrically isolate the logic circuit for control from the power output of the device, particularly if very high voltages are involved. Optocouplers are used to isolate a low voltage control from a high energy voltage. However, the use of a single optocoupler may not be strong enough to isolate higher energy voltages. Other devices of the prior art have used a double stacked optocoupler arrangement. However, such a double stacked arrangement may be limited to isolate the lower control voltage from a supply of approximately 240 volts. It is therefore desirable to provide an optocoupler arrangement that can isolate a low voltage control from high voltages such as 380 to 600 volts at 50 or 60 Hz. It is further desirable to provide a microcontrolled gate circuit capable of operating a wide variety of voltages. to the characteristics of the material fed on vibratory feeders or conveyors, it is often desirable to operate such equipment at low frequencies with longer travels. When the equipment is energized by an electromagnet, it is cost-effective and convenient to synthesize the lower operating frequency from the power source of 60 Hz to 50 Hz by omitting an appropriate number of half cycles of the line frequency. For example, from a power line of 60 Hz, frequencies can be obtained that are even submultiples of 120 pulses per second (7200 VPM) divided by 2 at 60 Hz, dividing by 3 at 40 Hz, between 4 at 30 Hz and so on. real "punctual" energy at any given frequency is limited to that of a half cycle at 60 Hz, it is desirable to capture as much available waveform as possible to maximize output power. Therefore, it is desirable to minimize the amount of time delay from the zero voltage crossover of the conductive waveform to the time the SCR is turned on., such as these can operate at power line voltages up to 600 volts AC While SCR's are available with inverse voltage scales of 1200 volts or more, because the requirement to control high voltage loads , highly inductive, generally impulse transformers are used to drive SCR's. However, pulse transformers can result in a large undesirable delay for driving the SCR and therefore not enough output power can be obtained. In addition to the cost of pulse transformers, it may be more difficult to make the control logic interface to the pulse transformer, and therefore a more expensive solution. Therefore, it is desirable to have a drive circuit that has a minimum delay in driving an SCR and is also cost effective.

Brief Description of the Invention A drive circuit comprising a diode, a capacitor and an SCR is provided wherein the diode charges the capacitor to drive the SCR. An opposing SCR drive circuit is also provided comprising a first and a second diode, a first and a second capacitor and an SCR wherein, the first diode loads the first capacitor to drive the SCR when a voltage line is positive and the second diode charges the second capacitor to drive the SCR when the line voltage is negative. An insulating circuit comprising at least three optocouplers placed in series is also provided wherein the optocouplers isolate a lower control voltage from a higher energy voltage Brief Description of the Drawings Figure 1 is an electrical circuit diagram of an individual SCR gate circuit of the present invention. Figure 2 is an electrical circuit diagram of an opposing SCR gate circuit of the present invention. Figure 3 is an illustration of a voltage waveform and the submultiple operation to activate the load. Figure 4A is an illustration of the positive cycle of the voltage waveform. Figure 4B is an illustration of the gate pulse from the microcontroller. wave that illustrates the voltage across the load Description of the Preferred Modalities Referring to Figure 1, an electrical circuit diagram of an individual SCR gate circuit 10 of the present invention is shown. A microcontroller, not shown, provides a signal 12 for driving an SCR by means of the circuit described. of the microcontroller 12 can be provided to a resistor 14 of 2.2 ohms, which, in turn, provides it to the base of the transistor 16. The transistor 16 can be, for example, an MPS4124 transistor manufactured by Motorola. The collector of transistor 16 can be connected to a resistor 18 of 220 ohms which, in turn, is connected to a power source 20 of 5 volts. The collector of the transistor 16 can also be provided to a first input 22 of an optocoupler circuit 24. A second input 26 of the optocoupler circuit 24 is connected to a first input 28 of a second optocoupler circuit 30. A second input 32 of the optocoupler circuit 30 is connected to the first input 34 of a third optocoupler circuit 36. The second input 38 of the third optocoupler circuit 36 may be connected to the emitter of the transistor 16 as well as to a ground 40 of 5 volts. The optocoupler circuits 24, 30, 36 can be an MOC3052 optocoupler circuits manufactured by Motorola. Placed between the outlets 42, 44 of the first optocoupler circuit 24 is a resistor 46 which can be a 1 ohm resistor. Similarly, placed between the outputs 48, 50 of the second optocoupler circuit 30 and the outputs 52, 54 of the third optocoupler circuit 36 may be resistors of 1 ohm 56 and 58 respectively. Furthermore, as shown, the resistor 46 is connected to the resistor 56, which, in turn, is connected to the resistor. The output 42 of the first optocoupler circuit 24 may also be connected to the resistor 60 which may be a 15 ohm resistor. The resistor 60 can, in turn, be connected to another resistor 62 that can be a 3K ohms resistor. The resistor 62 can, in turn, be connected to the output of a diode 64. The diode 64 can be a diode 1N4007 manufactured by Motorola. The input of the diode 64 is connected to the output of a load 66. The load 66 can be an equipment such as a variable frequency feeder. A first line 68 is provided to the load 66 for connection to an AC supply source. The resistor 60 can be connected to a capacitor 70 which can be a capacitor 0 1 μF The capacitor 70 can also be connected to a second line 72 as well as to a resistor 74 The resistor 74 can, for example, be a 1 2H ohms resistor. The opposite end of the resistor 74 may be connected to the second output 54 of the third optocoupler circuit 36 as well as to the input of the diode 76. The diode 76 may be a diode 1N4007. The output of the diode may be provided to the LED 78, which in turn, is provided to the gate terminal of the SCR 80. The input of the SCR 80 is provided from the load 66 and the output is provided to the line 72.

In operation, the signal 12 from the microcontroller can be a low voltage digital signal. Specifically, digital logic can be used to turn on and off the optocouplers to operate the SCR 80 as required. Alternatively, the analog circuit can be used to turn the optocouplers on and off in order to operate the SCR 80 as it is done in the normal industry. As shown, three optocouplers 24, 30 and 36 help isolate the low control voltage of signal 12 from load 66 which, for example, can be as high as 380 to 600 volts. As a result, the signal 12 can, in turn, be provided to drive the SCR 80 while protecting the microcontroller and the other related circuits from the high voltage load 66. The load on the capacitor 70 is used to periodically disconnecting the SCR 80 Specifically, when the optocouplers 24, 30 and 36 are turned on, the energy stored in the capacitor 70 is dissipated within the gate of the SCR 80 by means of the optocouplers. As a result, the optocouplers 24, 30 and 36 serve as solid state switches When the optocouplers are turned on, the circuit allows the capacitor 70 to periodically disconnect the SCR 80 A 1 the reverse, the optocouplers are off, the SCR 80 is not driven The diode 64 is used to maintain a full charge over capacitor 70 even when the line voltage 68. 72 is zero to allow the SCR 80 to be periodically disconnected at low or no voltage However, for In the embodiment shown in Figure 1, the SCR 80 can be operated only when the line voltage 68 is positive. That is, in applications where the load is driven when the AC line voltage is only positive, the drive circuit can be used. of SCR 10 Since the diode 64 is connected to the anode of the SCR 80, the capacitor 70 is charged with the correct polarity during the interval when the SCR 80 is not conducting. That is, the capacitor 70 loads when the line voltage 68 is positive and the SCR 80 is not actuated The load on the capacitor 70 is connected to the gate of the SCR 80 through an opto-coupled solid state switch (i.e., the tpac located within each of the optocouplers 24, 30, 36) The diode 64 also helps to allow the capacitor to maintain its high charge level when the line voltage 68 is low. The resistors 60 and 62 are sized to limit the current supplied to the comp rt of the SCR 80 when the AC line voltage is at its peak level so as not to exceed the maximum current scale of optocouplers 24, 30 and 36 When the AC line voltage is at a low level, resistors 60 and 62 limit the current at an insufficient level to periodically disconnect the SCR 80 The load on the capacitor 70 has a leveling effect on the AC line voltage which can provide a more constant voltage level to drive the SCR 80 That is, when the AC line 68 reaches its peak voltage, the capacitor 70 is charged to a high level corresponding to the AC line peak voltage. The capacitor 70 maintains approximately that high voltage until the activation of the SCR 80 occurs. When the SCR 80 is driven, the load on the capacitor 70 is dissipated and recharged when the AC line voltage 68 becomes positive. In addition, the capacitor 70 charges up to its high level when the line voltage reaches its peak value since the capacitor 70 is charged during the standby interval of the SCR 80, enough energy is stored to provide a stable and reliable drive pulse at or slightly leading to the zero crossing of the desired conductive waveform. This helps to ensure the maximum output voltage that it can be obtained through a wide range of ambient operating temperatures found in industrial environments (for example, from 48 8 ° C to -40 ° C) In addition, the RC network formed by capacitor 70 and resistor 62 is used to dampen or suppress transient voltages through SCR 80 Another advantage of diode 64 is that it removes the AC from the capacitor 70 This provides protection for the capacitor 70 and may allow the use of a lower voltage capacitor since the capacitor's AC voltage scales are much lower than its DC voltage scales. The resistor 74 keeps the gate voltage low when it is not operated. and helps to avoid self-action Resistor 74 allows the current to return inside line 72 instead of the gate of SCR 80 A lower gate potential, lower probability that SCR 80 could be driven by line noise Several circuits optocouplers 24, 30 and 36 are connected in series using a suitable resistance network (i.e., resistors 46, 56 and 58) to balance the voltage drop across each device to obtain the blocking voltage scales sufficient to withstand the peak of the applied line voltage plus an appropriate safety factor That is, the equilibrium resistors 46, 56 and 58 allow a small amount of current pass through optocouplers 24, 30 and 36 when the optocouplers are off Although three optocoupler circuits have been shown in series, only one optocoupler circuit can be used. Furthermore, more than three optocoupler circuits can be used to isolate higher line voltages. reverse voltage and current in the gate circuit (the gate circuit comprises all the elements shown in Fig. 1 except load 66, SCR 80 and lines 68 and 72). Diode 76 blocks the reverse current flow that does not must occur unless the SCR fault is present. In such a case, the gate circuit would be protected. The LED 78 only indicates that the gate current or pulse is present and not required for circuit operation. Referring now to the Fig 2 shows an alternative embodiment of the present invention wherein two SCR gate circuits 10, 10 'are used to form a circuit SCR door in opposition 90 For clarity purposes similar components have been similarly labeled and the numbers that have a prime designation reflect the second SCR gate circuit. It should also be noted that the signal 12 from the microcontroller, the voltage supply 20 of 5 volts, earth 40 of 5 volts, lines 68 and 72 as well as load 66 are common for both circuits. The opposing SCR drive circuit 90 comprises a first diode 64 and a second diode 64 ', a first capacitor 70 and a second capacitor 70' and an SCR 80. The first diode 64 loads the first capacitor 70 to drive the SCR 80 when the line voltage 68 is positive and the second diode 64 'loads the second capacitor 70' to drive the SCR 80 when the line voltage is negative. In addition, the first capacitor 70 is charged when the line voltage is positive and remains unchanged until the SCR 80 is driven during a positive cycle of the line voltage 68 and the second capacitor 70 'is charged when the line voltage is negative and remains charged until the SCR 80 is driven during a negative cycle of the line voltage 68. The opposing SCR drive circuit 90 may further comprise a first isolating circuit for isolating the control signal 12 used to drive the load when the line voltage 68 is positive and a second insulator circuit for isolating the control signal 12 used to drive the load when the line voltage is negative. The first insulator circuit comprises at least one optocoupler circuit 24 although it preferably comprises three optocoupler circuits 24, 30 and 36. Similarly, the second insulator circuit comprises at least one optocoupler circuit 24 'although preferably it comprises three optocoupler circuits 24', 30 'and 36'. The gate circuit SCR in opposition 90 allows conduction of the negative and positive halves of the line CA 68, 72 That is, the gate circuit of SCR in opposition 90 can be used when it is necessary to select half waves of opposite polarity As a result, in applications where the load is driven when the AC line voltage is positive and negative, the SCR gate circuit in opposition 90 can be used In other words, when the frequency energizing the load 66 is an odd submultiple of the frequency of line (ie the line frequency AC 68 multiplied by two divided by an odd number is necessary to energize the load 66) then the gate circuit of SCR in opposition 90 may be employed However, when the frequency energizing the load 66 is a submultiple pair of the line frequency (i.e., the line frequency CA 68 multiplied by two and divided by an even number is necessary to energize the load 66), the ignition circuit SCR 10 illustrated in Fig. 1 can be used. Figs 3 and 4 illustrate an example where an opposing SCR gate circuit can be employed. Referring specifically to Fig 3, a voltage waveform 100 of 3 to 60 Hz having a period of 001666 seconds as shown by 102 When a piece of equipment operates at 40 Hz, the period of the waveform is 0 025 seconds as shown by 104 The frequency that energizes the load 66 would be an odd submultiple of the line frequency since waveform 100 of 60 Hz multiplied by two (for the positive and negative phases of a waveform) and divided by three (the odd submultiple) results in a frequency of 40Hz to energize the load As a result, the equipment will be operated for a given positive half cycle 106 of the voltage waveform 100 and will not be driven during the subsequent two half cycles 108 110 of the voltage waveform 100. , will be driven once more during the negative half cycle 112 and would not be triggered during the two subsequent half cycles 114, 116 of the voltage waveform 100 It is desirable to turn on the equipment as close as possible to the point or zero crossing of the voltage waveform 100 to better energize the equipment. Referring also to FIG. 4A, a half cycle 118 of the voltage waveform as well as the zero crossing point 120 is shown. 4B the signal 12 from the microcontroller shown as a gate pulse 122 is provided to turn on the equipment in time 124 The activation circuit of the SCR 10 helps to minimize the delay 124 from the zero crossing point 120 to the point of operation of the SCR 80 As a result, the circuit helps to maximize the output available to energize the equipment or the load 66 Therefore, as shown in Figure 4C, the voltage across the load can be increased as much as the delay in the actuation of the SCR circuit it is reduced to a minimum. The SCR drive circuit 10 is able to have a relatively short delay 124 due to the fact that during the period of inactivity of the feeder, the capacitor 70 is charged even when the line voltage 68 is low. When the gate pulse 122 is provided, the capacitor 70 can be rapidly discharged into the SCR80 gate. In addition, the capacitor 70 also serves as a transient suppressor through the SCR 80. protecting the SCR 80 from the voltage spikes that can occur when switching highly inductive loads. The SCR 10 drive circuit can be used for high voltage control of feeders vibratory or electromagnetic at frequencies that are submultiples of the power line frequencies (ie, 60 Hz or 50 Hz) A variable frequency feeder can, for example, operate at 40 Hz. When using a 60 Hz line the opposing circuit 90 for energizing the load 66 The low cost SCR activation circuit described is useful in industrial control applications operating from high voltage power line sources such as 380 to 600 volts at a frequency of 50 or 60 Hz The invention would not only be useful to activate vibratory or electromagnetic feeders, would also be useful for other high-voltage applications that used omitted waveforms or other activation of SCR's in general high-voltage applications. It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art can develop a wide variation of the structural details without departing from the principles of the invention. Therefore, it is considered that the appended claims cover all equivalents that fall within the true scope and spirit of the invention.

Claims (1)

1. CLAIMS 1 A drive circuit comprising a diode, a capacitor, and a silicon controlled rectifier (SCR), wherein the diode loads the silicon controlled rectifier capacitor (SCR) 2 The invention of claim 1, wherein the diode is electrically connected at one end of the load and the capacitor is charged when a line voltage is positive. The invention of claim 1, wherein the capacitor is charged when a line voltage is positive and remains unchanged until the voltage is applied. silicon controlled rectifier 4 The invention of claim 3, comprising at least one resistor for limiting a given current to a gate of the silicon controlled rectifier when the line voltage is at a peak level and limiting the current to a level not enough to periodically deactivate the silicon controlled rectifier when the line voltage is at a low level The invention d e claim 2, wherein the load is driven when the line is positive 6 The invention of claim 1, further comprising at least one optocoupler for isolating a low control voltage from a high power voltage 7. The invention of claim 6, wherein said at least one optocoupler comprises three optocouplers placed in series 8 An opposing silicon contolado rectifier drive circuit comprising a first and second diode, a first and a second capacitor, and a rectifier controlled silicon (SCR), where the first diode charges the first capacitor to drive the silicon controlled rectifier (SCR) when one line voltage is positive and the second diode loads the second capacitor to drive the silicon controlled rectifier (SCR) ) when the line voltage is negative 9 The invention of claim 8, wherein the first capacitor is charged when the line voltage is positive and remains charged until the silicon controlled rectifier (SCR) is driven when the line voltage is positive and the second capacitor is charged when the voltage line is negative and remains charged until the rectifier Controlled Silicon (SCR) is driven when the line voltage is negative The invention of claim 8, further comprising a first insulator circuit for isolating a control signal for driving a load when the line voltage is positive and a second insulating circuit to isolate the control signal to drive the load when the line voltage is negative 11. The invention of claim 10, wherein the first insulating circuit comprises at least one optocoupler and the second insulating circuit comprises at least one optocoupler circuit. The invention of claim 11, wherein the first and second insulating circuits each comprise three optocouplers placed in series. 13. An insulating circuit comprising: at least three optocouplers placed in a row where the optocouplers isolate a low control voltage from a high energy voltage. The invention of claim 14, wherein the isolating circuit is used to isolate a signal from a microcontroller to energize a vibratory feeder.