CN109478777B

CN109478777B - Control circuit and high-frequency circuit breaker

Info

Publication number: CN109478777B
Application number: CN201780029959.XA
Authority: CN
Inventors: 郑家伟; 薛向党
Original assignee: Hong Kong Polytechnic University HKPU
Current assignee: Hong Kong Polytechnic University HKPU
Priority date: 2016-03-14
Filing date: 2017-03-14
Publication date: 2020-05-22
Anticipated expiration: 2037-03-14
Also published as: WO2017157288A1; CN109478777A

Abstract

High Frequency Circuit Breakers (HFCBs) and control circuits for HFCBs are provided. The HFCB includes a control circuit, a sensing circuit, and a power circuit. The sensing circuit senses at least one of a high frequency leakage current and a high frequency current through the load, and the power circuit connects and disconnects power to the load. The control circuit includes an analog comparator and a switching state holding circuit. An analog comparator compares an output from the sensing circuit to a current reference, and a switching state holding circuit provides a control signal to the power circuit based on the output from the analog comparator to force the power circuit to selectively connect power to the load or disconnect power to the load.

Description

Control circuit and high-frequency circuit breaker

Priority requirement

This application claims priority from the united states provisional patent application No. 62/307,589.

Technical Field

Disclosed below are a control circuit for a circuit breaker, and a circuit breaker including the same. In particular, a control circuit and circuit breaker for monitoring current in a high frequency alternating current system are disclosed.

Background

In many modern systems, it is desirable to use a high frequency Alternating Current (AC) electrical distribution. Such systems are used in space stations, electric vehicles, renewable energy micro grids, telecommunication systems and computer systems. High frequency AC operates at 20kHz to 50kHz and has many potential benefits, including: a compact high frequency transformer can be used, contributing to a substantial reduction in the number and volume of electrical components, and to an improvement in dynamic response, reduction and elimination of acoustic noise.

Under normal circumstances, the energized (live) line and the return (neutral) line are expected to carry the same current. Any difference typically indicates the presence of an electrical anomaly. This difference is referred to as residual current or leakage current.

In the case of leakage currents through the human body, even small leakage currents pose a risk of electrocution injury or death. A leakage current of about 30mA through the human body may be sufficient to cause a sudden cardiac arrest or severe injury if it lasts for a fraction of a second or more.

As systems become more complex, and as they age and degrade, the likelihood of leakage current increases. In order to reduce the risk of damage from leakage currents, Residual Current Devices (RCDs) or Residual Current Circuit Breakers (RCCBs) are installed in the circuit to quickly break the current and thereby prevent serious damage from prolonged shocks.

Conventional low frequency residual current circuit breakers are not suitable for high frequency AC systems due to the fast response of high frequency AC. However, the design of high frequency AC circuit breakers that can operate reliably and respond quickly to changes in leakage current has been a challenging problem.

Disclosure of Invention

The present disclosure provides a control circuit for a High Frequency Circuit Breaker (HFCB), the HFCB comprising: a sensing circuit for sensing at least one of a high frequency leakage current and a high frequency current through a load; and a power circuit for connecting and disconnecting power to and from a load, the control circuit comprising:

an analog comparator for comparing an output from the sensing circuit to a current reference; and

a switched state retention circuit for providing a control signal to the power circuit based on the output from the analog comparator to force the power circuit to selectively connect power to the load or disconnect power to the load.

The control circuit may be used for HFCBs whose sensing system senses high frequency residual currents. The control circuit may be used for HFCBs whose sensing system senses high frequency current (i.e., load current). The control circuit may be used in an HFCB whose sensing system senses high frequency residual current and high frequency current.

The output of the analog comparator may be based on a difference between the output from the sensing circuit and the current reference.

The output from the sensing circuit may include a voltage, the current reference includes a voltage indicative of a threshold current, and the analog comparator identifies the voltage difference. The threshold current may be a threshold leakage current. The threshold current may be a threshold load current. The sensing circuit may sense both the leakage current and the load current, and the comparator may identify a voltage difference between each current and its respective threshold.

The analog comparator may include a high speed comparator Integrated Circuit (IC).

The analog comparator may include a differential operational amplifier (OpAmp) for determining a difference between an output from the sensing circuit and the current reference. The OpAmp and the current reference may be driven by a common Direct Current (DC) input voltage.

The current reference may include a variable impedance and an impedance, and varying the impedance of the variable impedance adjusts the current reference.

The output from the analog comparator may have multiple states. In particular, the output from the analog comparator may have a first state indicating that the output from the sensing circuit does not exceed the current reference, and a second state indicating that the output from the sensing circuit exceeds the current reference.

The control signal from the switched state retention circuit may have a plurality of states. In particular, the control signal from the switched state retention circuit may have a first control state for forcing the power circuit to connect power to the load and a second control state for forcing the power circuit to disconnect power to the load. Once the output from the analog comparator switches from the first state to the second state, the control signal may switch from the first control state to the second control state. In the case where the control signal reaches the second state, the control signal can maintain the second state regardless of a change in the output from the analog comparator.

The control circuit may further comprise a reset switch, activation of which forces the switching state holding circuit into the first state if the output of the analog comparator is in the first state.

The switching state holding circuit may include a NOR (NOR) circuit including a plurality of NOR gates and an inverter circuit including a plurality of inverters. Two of the NOR gates may be used to hold the second state of the switched state holding circuit, wherein:

each of the two NOR gates providing an input to the other NOR gate;

the inputs of the two NOR gates are affected by the activation of a reset switch; and

the input of the other of the two NOR gates is affected by a change in the output of the analog comparator from a first state to a second state.

The present disclosure also provides a High Frequency Circuit Breaker (HFCB) comprising a control circuit as described above. This may be an HFCB comprising:

a control circuit;

a sensing circuit for sensing at least one of a high frequency leakage current and a high frequency current through a load; and

a power circuit for connecting and disconnecting power to a load,

wherein, the control circuit includes:

The power circuit may include a relay and a switch, each of which is switchable between an on state and an off state. The relay and the switch may be connected in series such that: if any of the relay and the switch is switched to the off state, the connection of the power to the load is disconnected. Alternatively, the relay and the switch may be connected in parallel such that: once either one of the relay and the switch is switched to the on state, power is connected to the load.

Some embodiments provide the present circuit breaker, which enables one or both of the following:

(i) if the detected high frequency leakage current is greater than a specified Root Mean Square (RMS) value, e.g., 30mA, the high frequency AC current can be turned off for a specified duration, e.g., 40 ms; and

(ii) if the detected high-frequency load current is larger than a specified current value, the high-frequency AC current can be quickly turned off. This may occur in the event of an overload or a short circuit.

Accordingly, some embodiments may provide a High Frequency Residual Current Circuit Breaker (HFRCCBO) with overcurrent (excessive load current) protection. This is a device for quickly breaking current to prevent serious injury from sustained electric shock and to prevent overheating or fire risk due to short circuit or overcurrent due to an overloaded circuit. The present HFRCBO can provide leakage current protection as well as overload or short circuit protection in high frequency AC systems.

In some embodiments, the specified leakage current and/or the specified load current may be flexibly adjusted to suit a particular application.

A control circuit as described above, wherein the control circuit is to receive an output from a sensing circuit, the sensing circuit comprising:

a first high frequency current transducer for sensing load current and leakage current; and

a second high frequency current transducer for sensing the other of the load current and the leakage current; and is

The control circuit includes:

a first sub-circuit, comprising:

a comparator as a first comparator for comparing the output from the first high frequency current transducer with a respective load current reference or leakage current reference; and

a switching state holding circuit as a first switching state holding circuit; and

a second sub-circuit, comprising:

a second analog comparator for comparing the output from the second high frequency current transducer with a respective load current reference or leakage current reference; and

a second switching state holding circuit for providing a control signal to the power circuit based on the output from the second analog comparator to force the power circuit to selectively connect power to the load or disconnect power to the load.

The sensing circuit may include a DC residual current transducer and two AC-DC rectifiers. The power circuit may comprise two outputs, the load may comprise two terminals, and the AC-DC rectifiers may each comprise an input, wherein one output of the power circuit and one terminal of the load provide the AC input to one of the two AC-DC rectifiers and the other output of the power circuit and the other terminal of the load provide the other AC input to the other of the two AC-DC rectifiers. Each AC-DC rectifier may comprise a DC output and the difference between the DC outputs provides an input to a DC residual current transducer, and the output of the DC residual current transducer is isolated from the input of the DC residual current transducer.

Drawings

Some embodiments of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

fig. 1 is a block diagram of a high frequency circuit breaker according to the present disclosure;

fig. 2a is a schematic diagram of a High Frequency Residual Current Circuit Breaker (HFRCCBO) with overcurrent protection providing quick disconnect;

FIG. 2b depicts a schematic structure of HFRCCBO for providing fast connection and low conduction loss;

FIGS. 3a and 3b are schematic diagrams of a power circuit and a sensing circuit, wherein FIG. 3a employs a high frequency residual current transducer and FIG. 3b employs a DC leakage current transducer;

FIG. 3c depicts the AC supply voltage, breaker control voltage, load voltage and load current for the circuit of FIGS. 3a and 3 b;

fig. 4 is a schematic diagram of a High Frequency Residual Current Circuit Breaker (HFRCCBO) with overcurrent protection;

FIG. 5 is a schematic diagram of a control circuit divided into three sub-circuits, control circuit A, control circuit B, and control circuit C;

FIG. 6a shows an embodiment of the control circuit A of FIG. 5;

FIG. 6b depicts a typical waveform expected to pass through the control circuit A of FIG. 6 a;

FIG. 7a shows an embodiment of the control circuit B of FIG. 5;

FIG. 7B depicts a typical waveform expected to pass through the control circuit B of FIG. 7 a;

FIG. 8a illustrates an embodiment of the control circuit C of FIG. 5;

FIG. 8b depicts a typical waveform expected to pass through the control circuit C of FIG. 8 a;

fig. 9 depicts typical waveforms presented by a high frequency AC circuit employing a High Frequency Circuit Breaker (HFCB) as described herein.

Detailed Description

Broadly, the present disclosure provides a control circuit and circuit breakers, each circuit breaker including at least one of:

a control circuit;

a power circuit; and

a sensing circuit.

The circuit breaker is a High Frequency Circuit Breaker (HFCB) because the control circuit can operate at high frequencies and can be used to create fast control signals for connecting and disconnecting the high frequency AC power source to the load.

In some embodiments, no power circuitry and sensing circuitry may be provided, and only control circuitry may be provided. The control circuitry may then be coupled with various power and sensing circuitry to provide the desired functionality. The control circuit does not use a microcontroller unit (MCU). Alternatively, the control circuit is entirely composed of analog and logic components. The control circuit shown herein provides fast detection and fast disconnection in the face of leakage and/or over-current, in the case of purely analog and logic components. Additionally, in some embodiments, the leakage current reference and/or the overcurrent reference may be flexibly changed depending on the need. Thus, the control circuit may be adjusted to detect a current of a desired magnitude.

Fig. 1 provides a block diagram illustrating an embodiment of a circuit 100 including a high frequency residual current circuit breaker 102. The circuit breaker 102 may also provide overcurrent protection.

HFAC 104 represents a high frequency AC power source for supplying power to load 106 through circuit breaker 102. The circuit breaker 102 includes a power circuit 108, a sensing circuit 110, and a control circuit 116.

Power is transferred from HFAC 104 through power circuit 108, power circuit 108 being used to connect high frequency AC power source 104 to load 106 and disconnect high frequency AC power source 104 to load 106 in the event of a detected leakage and/or overcurrent. The power circuit 108 is composed of a relay/isolator and an electric switch. Each of the relay and the switch is capable of switching between an on (i.e., conductive) state and an off (i.e., non-conductive) state. These are actuated by the control circuit 116.

After passing through the power circuit 108, the power passes through the sensing circuit 110 and to the load 106. The sensing circuit 110 detects one or both of a load current and a leakage current. The load current may be detected by detecting the current only on the power main 112. In contrast, leakage current is the difference between the current delivered from the load 106 and the current received from the load 106, thus requiring measurement of both the live line 112 and the return line 114.

The control circuit 116 is then used to compare the load current and/or leakage current sensed by the sensing circuit 110 to a reference load current and/or reference leakage current. The control circuit 116 determines whether any current change relative to the associated reference current is within allowable limits. If so, the circuit remains closed and power may continue to flow to the load. If the current change is outside of the allowable limit, the control circuit 116 forces the power circuit 108 to disconnect power from the load.

The sensing circuit is made up of one or more high frequency current transducers. Transducers may be used to detect one or both of leakage current and overcurrent and may therefore include one or both of a high frequency leakage current transducer and a high frequency overcurrent (or load current) transducer.

The sensing circuit converts the detected current into a voltage output. The output is then sent to the control circuit.

The control circuit is composed of analog components. The control circuit is used to compare one or both of: the detected leakage current and the specified leakage current, and the detected load current and the specified load current. Based on the comparison, the control circuit generates control signals to force the power circuit to connect (including maintain a connection) or disconnect power to the load. In order to be able to be used with small current variations, for example in the case of very small threshold values for tolerable leakage currents, the control circuit also amplifies the control signal to a level sufficient to drive the relay/isolator and/or the electrical switch of the power circuit.

Fig. 2a and 2b provide schematic structures of 200, 200' of a High Frequency Residual Current Circuit Breaker (HFRCCBO) with overcurrent protection. Fig. 2a shows a schematic structure enabling a quick disconnect. This is achieved by placing a switch 228 and a relay 226 in series. Thus, switching either of the switch 228 and the relay 226 open disconnects the power from the load. Fig. 2b depicts a schematic structure enabling fast connection and low conduction losses. This is achieved by arranging a switch 228 'and a relay 226' in parallel. Thus, connection of either of the switch 228 'and the relay 226' will result in connection of power to the load, and the resistance through the power circuit 224 is reduced when compared to the series resistance.

Both fig. 2a and 2b provide a sensing circuit 202 that senses both leakage current and load current. This is to prevent overcurrent, i.e., excessive load current, and excessive current leakage. The sensing circuits 202 each include a High Frequency Leakage Current Transducer (HFLCT)210 for sensing leakage current and a High Frequency Current Transducer (HFCT)212 for sensing load current.

Similarly, the control circuit 204 compares (i) the converted voltage representing the detected leakage current to a leakage current reference or specified leakage current 206 and/or (ii) the converted voltage representing the load current to a load current reference or specified load current 208. In some embodiments, the sensing circuit 202 may sense only one of the two currents, so the control circuit 204 need only compare the sensed current to its references 206, 208.

Typically, the current references 206, 208 are each set to a voltage for preparing a comparison with the voltage output by the sensing circuit 202 as a conversion quantity proportional to the associated sensed current.

The current references 206, 208 are quantities (e.g., voltages) that indicate respective current thresholds. When the sensed current exceeds the threshold, it triggers an over-current or leakage current event. The word "indication" is used because the design of the circuit may be such that: (i) the sensed current equal to the threshold is the maximum allowable overcurrent or leakage current, or alternatively, (ii) the sensed current equal to the threshold is the minimum or lowest current that will trigger overcurrent or leakage current protection. Thus, both interpretations of "threshold" are intended to be covered by the word "indicate".

The control circuit 204 provides

comparators

214, 216 for each sensed current. The output of the

respective comparator

214, 216 is designed to be high or high if the output of the

respective comparator

214, 216 indicates that the associated sensed current does not exceed its threshold indicated by the current reference. Conversely, a low output indicates that the current is at least as high as the threshold. However, it will be appreciated that a low or low level output may be similarly used to convey the same information, and in this case either the high comparator output or the low comparator output will need to be inverted before being input to the and gate discussed below.

Under normal conditions, the load current is less than the specified load current 208. Thus, the output of the High Frequency Current Transducer (HFCT)212 is less than the current reference 208. Therefore, the output of comparator 216 is high. Comparator 216 accomplishes this by subtracting one voltage from the other. In other words, the comparator 216 may measure the voltage difference. The difference will be at least zero if the output of the HFCT 212 is at most equal to the current reference 208, i.e., does not exceed the current reference 208, resulting in a high output; and the difference will be negative if the output of the HFCT 212 is greater than the current reference 208, resulting in a low output. Alternatively, the current reference in each case can be defined such that: if the sensed current is at least equal to the current reference, the output is low; otherwise, the output is high.

Similarly, under normal conditions, the leakage current is less than the specified leakage current 206. Thus, the output of the High Frequency Leakage Current Transducer (HFLCT)210 is less than the leakage current reference, and thus, the output of the comparator 214 is high.

The present circuit 200 also includes an on/off switch 218. The on/off switch 218 may be a manual switch for initiating power delivery to the load. For example, the on/off switch 218 may be an ignition button of an electric vehicle. The output of the on/off switch 218 is high if the switch 218 is on and low if the switch 218 is off.

The output from each of the

comparators

214, 216 and the on/off switch 218 is delivered to an and gate 220. The operation of and gate 220 will be understood by the skilled person.

All three inputs to and gate 220 are high because normal conditions cause the outputs of

comparators

214, 216 and on/off switch 218 to be high. The output of and gate 220 is therefore high.

In embodiments where the current is to be delivered continuously, the on/off switch 218 may not be included. Additionally, as described above, some embodiments may only require sensing one of leakage current and load current. In embodiments where an on/off switch is not required and only a single current is sensed, an and gate will not be required.

The output of and gate 220 may be delivered to amplifier 222. Most likely, in the circuits 200, 200', the output of the and gate 220 is insufficient to drive the power circuit 224. In the case where the output of the and gate 220 is sufficient to drive the power circuit 224, no amplifier is required.

In the embodiment shown, an amplifier 222 is present. The amplifier 222 amplifies the output of the and gate 220 to a level that can drive the power circuit 224-in other words, to a level sufficient to actuate or drive relays and switches in the power circuit 224.

The power circuit 224, 224' includes a relay or isolator (Re)226, 226' and an electrical Switch (SE)228, 228 '. The output of the amplifier 222 drives relays or isolators (Re)226, 226 'and electrical switches (Se)228, 228'. Thus, Re226, 226 'is on, and Se 228, 228' is on. Thus, high frequency AC power is supplied from the power supply 230 to the load 232. Similarly, if the switch 218 delivers a stop command (open) or the output from one of the

comparators

214, 216 is low, Re226, 226 'and Se 228, 228' are open and the connection of the high frequency AC current to the load 232 is open.

During abnormal operating conditions, the output of the HFCT 212 and/or HFLCT 210 is greater than the load current reference 208 and/or the leakage current reference, respectively. In other embodiments, abnormal operation will be indicated by the output being at least equal to the current reference and/or the leakage current reference. In the event that the detected leakage current is greater than the specified leakage current 206, the output of comparator 214 is low. Regardless of the output of the comparator 216 or the switch 218, the output of the and gate 220 will be low and Re226, 226 'and Se 228, 228' are turned off. The output of comparator 214 remains low to maintain leakage current protection.

Regardless of the output from the HFLCT 210, the comparator 214 remains low until the comparator 214 is reset by activating the reset 234. Reset 234 resets comparator 214 so that the output of comparator 214 is again dependent on the output of HFLCT 210. If the output of the HFLCT 210 indicates that the leakage current exceeds the leakage current reference 206, the output of the comparator 206 will again be driven low. The comparator output will be high only if HFLCT 210 indicates that the leakage current does not exceed the leakage current reference 206.

Similarly, where the output of the HFCT 212 is greater than the current reference 208, the output of the comparator 216 is low. The output of and gate 220 is therefore also low and Re226, 226 'and Se 228, 228' are off. The output of comparator 216 remains low to provide overcurrent protection until reset 236 is activated.

Fig. 3a and 3b are schematic diagrams of a power circuit and a sensing circuit. Fig. 3a employs a High Frequency Leakage Current Transducer (HFLCT). Fig. 3b employs a DC leakage current transducer (DCLCT).

In the power circuit 300, the relay (Re)302 is comprised of a control coil 304 on the circuits R _ A-R _ B and two-pole normally

open contacts

306, 308 on the circuits R _4-R _7 and R _6-R _9, respectively, as discussed with reference to FIG. 8a, the circuits R _4-R _7 isolate the start switch 822.

If the DC voltage across the control coil 304 is 0V, caused by the low state of the output of the AND gate 220, the two-pole normally

open contacts

306, 308 are open. If the DC voltage across the control coil 304 is equal to a specified DC voltage (e.g., 12V) caused by the high state of the output of the AND gate 220, the two-pole normally

open contacts

306, 308 are closed. Thus, the relay 302 is able to connect and disconnect high frequency AC current.

The relay 302 may be an electromagnetically actuated relay in which the coil 304 is electromagnetic and energizing the coil 304 pulls one contact of each of the two pole normally

open contacts

306, 308 toward the other respective contact, thereby closing the

contacts

306, 308 and forming a conductive circuit of the

contacts

306, 308.

Any suitable relay may be used in place of relay 302.

The power circuit 302 also includes an electrical switch 310. The electric switch 310 is composed of switch parts (Mp-312 and M)_n-314), fast diode (D)_p-316 and D_n-318), a resistor (R)_p-320、R_n-322 and R_s-324) and a capacitor (C)_s-326).

The switching component 312 and the fast diode 318, which are currently represented by transistors, form a conducting circuit in the following cases:

the high frequency AC voltage is positive; and is

Transistor M_p(312) Gate (G) of_p) And source (S)_p) A drive voltage V between_GpTo the voltage specified for activating the transistor 312-i.e., high.

In the same way, the switching component 314 and the fast diode 316, which are now also represented by transistors, form a conducting circuit in the following cases:

the high frequency AC voltage is negative; and is

Transistor M_n(314) Gate (G) of_n) And source (S)_n) A drive voltage V between_GnTo the voltage specified for activating the transistor 314-i.e., high.

Conversely, if the drive voltage between the associated gates is low, e.g., 0V, the transistor is turned off.

The electrical switch is capable of connecting and disconnecting high frequency AC

current using transistors

312, 314. More specifically, the

transistors

312, 314 may operate using small voltages applied to the gates, and those small voltages may change rapidly. Thus, the

transistors

312, 314 can use a small voltage that varies rapidly to control the much larger current passing from the source to the sink.

The High Frequency Current Transducer (HFCT)328 has a DC voltage input (VCC), a ground input (GND), and an output (V)_M). The detected load current is isolated from VCC, GND and M. This may be accomplished using any of a number of sensors. For example, a hall effect sensor can sense current without being physically connected to a live or return line. Voltage (V) of output_M) In proportion to the change in the high frequency current.

The High Frequency Leakage Current Transducer (HFLCT)330 in FIG. 3a has a positive supply voltage (+ V), a negative supply voltage (-V), Ground (GND), and an output (V)_HFLCT). Live and return lines and + V, -V, GND and V_HFLCTAnd (4) isolating. Output (V)_HFLCT) Proportional to the difference between the energized high frequency current and the returned high frequency current.

In the circuit of fig. 3b, the HFLCT is replaced by a DC leakage current transducer (DCLCT) 332. The transducer 332 comprises an AC-DC-AC converter comprising two

full bridge rectifiers

334, 336. Rectifier 334 includes four fast diodes D_T1、D_T2、D_T3And D_T4And the rectifier 336 includes four fast diodes D_T5、D_T6、D_T7And D_T8。

When the high frequency AC voltage is positive, current passes through diode D_T3、D_T4、D_T5And D_T6Thus completing the circuit through HFLCT 332. Similarly, when the high frequency AC voltage is negative, current flows through diode D_T1、D_T2、D_T7And D_T8Thus completing the circuit through HFLCT 332.

The DC leakage current transducer (DCLCT)332 has a positive supply voltage (+ V), a negative supply voltage (-V), Ground (GND), and an output (V)_DCLCT). Live and return lines and + V, -V, GND and V_DCLCTAnd (4) isolating. Output (V)_DCLCT) Is proportional to the difference between the energized DC current indicative of the energized high frequency current and the returned DC current indicative of the returned high frequency current.

HFLCT330 and DCLCT 332 each include a DC-DC converter U₁(334). The converter 334 converts the external supply Voltage (VCC) into a positive voltage (+ V) and a negative voltage (-V) to match the positive and negative supply voltages of the HFLCT330 or the DCLCT 332. Adjusting the input to the converter 334 enables the HFLCT330 and the DCLCT 332 to be calibrated to sense a voltage of a desired amplitude.

In HFLCT, U₂(337) Is for the output V_HFLCTA high speed operational amplifier (OpAmp) that performs filtering and amplification. Similarly, in DCLCT, U₂(338) Is for the output V_DCLCTA high speed operational amplifier (OpAmp) that performs filtering and amplification. Output of OpAmp 337 (V)_RCDct) And V_HFLCTThe relationship between is represented as:

and the output (V) of the OpAmp 338_RCDct) And V_DCLCTThe relationship between is represented as:

in each case, R₁、R₂And R₃Is to provide an output from the OpAmp 337, 338 back to negativeA resistor group for negative feedback of the input terminal. R₃Is a variable impedance (i.e., adjustable regulator) used to calibrate the gain of the OpAmp 337, 338. This enables the OpAmp 337, 338 to be calibrated to apply appropriate gains for various magnitudes of leakage current. For example, in a first circuit, a leakage current of 5mA may be the maximum allowable leakage before power should be disconnected from the load. In the second circuit, the leakage current of 30mA may be the maximum allowable leakage. R₃The same HFLCT330 or DCLCT 332 is enabled in both circuits, and the gains of the opamps 337, 338 are adjusted so that the first and second circuits will output the same voltage if their respective thresholds are reached.

FIG. 3c depicts the voltage V across the relay 304 controlling the connection of the power source 340 to the load 342 in FIGS. 3a and 3b_RABTypical waveform response of the case. The power supply 340 provides an AC voltage V_ac。V_acHas no effect until V_RABHigh at point 344, at which time the gate voltages V of

transistors

312, 314_GpAnd V_GnAlternating high and low states. Thus, the

transistors

312, 314 are activated in an alternating manner. The power is transferred to the load 342, causing a voltage V across the load 342_LoadAnd current I_Load。

Fig. 4 is a schematic diagram of a High Frequency Residual Current Circuit Breaker (HFRCCBO)400 with overcurrent protection, showing various signals passed between a control circuit 402 and power circuitry and a sensing circuit 404 and external inputs and outputs. VCC and GND provide an external DC power supply (e.g., a 12V DC power supply) that provides power to both the sensing circuit 404 and the control circuit 402. The AC _ IN1 and AC _ IN2 are connected to a high frequency AC power source. The AC _ OUT1 and the AC _ OUT2 are connected to a load. These inputs and outputs are further defined with reference to fig. 5, 6a, 7a and 8 a.

For purposes of illustration, as schematically shown in fig. 5, control circuit 500 is divided into three sub-circuits, control circuit a (502), control circuit B (504), and control circuit C (506). The control circuit a (502), shown in detail in fig. 6a, provides a control signal (V) for controlling the overcurrent protection_OCb). Shown in detail in figure 7aThe control circuit B (504) provides a control signal (V) for controlling leakage current protection_RCDb). The control circuit C (506), shown in detail in FIG. 8a, implements a start-up cycle or start cycle (switch on-S) of HFRCCBO_ON) And off cycle of HFRCCBO (switch off-S)_OFF)). The control circuit C (506) also generates a synchronization signal for the electrical switch, the drive voltage for the two switching components (e.g., G for transistors 312, 314)_p-S_pAnd G_n-S_n) And the drive voltage (R _ a-R _ B) of the control coil 304 of the relay 302.

With further reference to FIG. 5:

V_RCDctis a leakage current signal from the sensing circuit, is an input to the control circuit B (504);

T₁and T₂Is connected to a power circuit for test leakage current protection and is an input of a control circuit B (504);

V_Mis the load current signal from the sense circuit, is the input to the control circuit a (502);

VCC and GND are external DC supplies (e.g., 12V DC supplies) that supply power to the sensing and control circuits;

AC _ IN1 and AC _ IN2 are connected to the high frequency AC power source and acquire synchronization signals for the high frequency AC voltage, and are inputs to the control circuit C (506);

r _4 and R _7 are contacts of the relay 302 in the power circuit, and are outputs of the control circuit C (506);

r _ a and R _ B are connected to the control coil of the relay in the power circuit and are the outputs of the control circuit C (506);

G_p-S_pand G_n-S_nControlling the drive gate voltage for the switching

components

312, 214 is currently two metal oxide semiconductor field effect transistors (MOSFET-M) in the power circuit, respectively_pAnd MOSFET-M_n)。

Fig. 6a shows the provision of a control signal V for controlling overcurrent protection_OCbExemplary embodiment of control circuit a (502). As discussed above, circuit 502 is used for high frequency disconnectionA High Frequency Circuit Board (HFCB) includes a sensing circuit for sensing current through a load, and a power circuit for connecting and disconnecting power to the load. In the embodiment shown in FIG. 6a, the control circuit (or sub-circuit as the case may be) includes an OpAmp U₃(600) And a switched state holding circuit 608.

The analog comparator 606 will output (V) from the sensing circuit_M) With a current reference (V)_OCref) A comparison is made. And the switch state holding circuit 608 provides a control signal to the power circuit (see 224 of fig. 2a and 224' of fig. 2 b) based on the output from the analog comparator to force the power circuit to selectively connect power to the load or disconnect power to the load. Using these

circuits

606 and 608, the control circuit 502 provides control signals for monitoring the load current and controlling the disconnection of the connection of power to the load in the event of an overcurrent.

Component U₃(600) Is a comparator that detects an overcurrent. Component 600 may be a high speed comparator Integrated Circuit (IC). As shown, the component 600 is an OpAmp. The OpAmp 600 is powered by VCC, and VCC also contributes to the positive feedback loop 602 of the component 600. Thus, the OpAmp 600 and the current reference are driven by a common Direct Current (DC) input voltage VCC.

A positive feedback loop provides a current reference. The current reference comprises a variable impedance (R)₆-604). The current reference now also includes an impedance (R)₈). Changing the impedance of the variable impedance 604 adjusts the current reference.

A current reference is applied at the positive terminal of the OpAmp 600 and a sensed load current is applied at the negative terminal of the OpAmp 600. Thus, if the current reference is greater than the sensed load current, the output of the OpAmp 600 will be high and the circuit 502 will operate normally. If the current reference is at least as large as the sensed load current, the output of the OpAmp 600 will be low and over-current protection will be triggered.

The output of the comparator circuit 606 is delivered to a switched state holding circuit 608. If the output of comparator circuit 606 is high, the switched state holding circuit 608 shown in FIG. 6a will hold the high outputGo out (V)_OCb). If the output of the comparator circuit 606 is low, the switched state holding circuit 608 shown in FIG. 6a will switch to a low output (V)_OCb)。

Referring to the embodiment shown in fig. 2a and 2b, the circuit 502 comprises the comparator 208. Thus, output (V)_OCb) From comparator 208 to and gate 220. Thus, the high output from comparator 208 will make the state of the AND gate dependent on its other inputs. Conversely, the low from comparator 208 pulls the AND gate output low. This low output will cause the power circuit 224, 224' to disconnect power to the load 232.

Ideally, the switching state retention circuit 608 should maintain a low output when an overcurrent event is experienced to ensure that the circuit does not resume normal operation until the overcurrent event is corrected. To facilitate state retention, e.g., to maintain a low output when an over-current event is experienced, the switching state retention circuit 608 includes a NOR (NOR) circuit. The NOR circuit includes a plurality of NOR gates.

NOR function pass-through unit U₄(610) And U₅(612) To be implemented. These components 610, 612 may be Complementary Metal Oxide Semiconductor (CMOS) NOR gate ICs.

Since circuit 502 is used in a high frequency environment, circuit 502 has a very short time to switch the NOR gate in the event of an overcurrent. The sinusoidal analog input only lasts for a brief period at its peaks (or valleys), but it may be desirable for the sinusoidal analog input to have a slightly longer period to ensure that changes in the state of the output of the NOR gate can propagate through circuit 502 before the input to circuit 502 changes. In other words to ensure proper NOR gate switching.

To provide a NOR gate input that is sufficiently persistent to facilitate switching and output propagation, the switching state retention circuit 608 includes a hysteresis block or hysteresis component U₆(614). The hysteresis component 614 has a non-linear relationship between its input and output to maintain the output despite small changes in its input. This also helps to cancel noise from its input. For example, if the component 614 output is low, it will only go high once the input exceeds a positive (i.e., high) threshold. Then, once the input exceeds — -I.e., to a negative (i.e., low) threshold, the component 614 output will simply go back low. This may cause the AC sinusoidal input to produce a square wave output through component 614. Advantageously, holding the value longer as implemented using a square wave gives the NOR gate enough time to change its output and has the following effect: the output propagates in circuit 502 before the input changes. Thus, at input V_MThe effect of the overcurrent may propagate through the switch state retention circuit 608 before it is reduced and no longer indicative of the overcurrent. This makes it possible to capture an overcurrent event even if the overcurrent event is not indicated on the input for a long time.

In this embodiment, the means 614 is constituted by an inverting schmitt trigger circuit. Although only three triggers are used, there are six triggers in the present component 614 as this is a standard component, however. The flip-flop functions as an inverter having a schmitt trigger operation at an input.

The hysteresis component 614 is used to control the indicator Lamp₁(Lamp)₁) (616) and clean up inputs-e.g., remove noise-to make it more reliable in controlling the switching of the NOR gates as described above. When there is no over-current, the lamp ₁616 is not bright. On the contrary, when overcurrent occurs, the lamp ₁616 light up.

If the output voltage (V) of the HFCT is_CT) (see, e.g., reference 328 in fig. 3a and 3 b) is less than the overcurrent reference (V)_OCref) Then the output voltage (V) of the comparator 602_OC) Is high. Due to V_OCHigh, switches the output (V) of the state holding circuit 608_OCb) Is high. Thus, the indicator Lamp₁(Lamp)₁) Not bright. In other words, the output from the analog comparator 606 may have multiple states. There are two current states, including an indication that the output from the sensing circuit (HFCT) does not exceed the current reference (V)_OCref) And indicates that the output from the sensing circuit (HFCT) exceeds the current reference (V)_OCref) Second state (low). Similarly, the control signal from the switched state retention circuit 608 may have multiple states. There are currently two states, including for forcing the power circuit to beA first control state (high) for power connection (including remaining connected) to the load and a second control state (low) for forcing the power circuit to disconnect power to the load. Further, once the output from the analog comparator switches from the first state (high) to the second state (low), the control signal sent from the switching state holding circuit 608 switches from the first control state (high) to the second control state (low).

In contrast, if the output voltage (V) of the HFCT is high_CT) Greater than the over-current reference (V)_OCref) Then V is_OCIs low. Due to V_OCLow, output (V) of component 606_OCb) Similarly low. Thus, the indicator Lamp₁(Lamp)₁) And (4) lighting. Thereafter, V_OCbIs kept at a low level, and the lamp₁Kept on until Reset switch Reset₁(reduction of position)₁) (622) triggered-e.g., pressed in the case of a reset button.

In practice, the switched state holding circuit 608 has two states. As discussed above, switching the switched state holding circuit 608 to the second low state depends on the input from the analog comparator 602. However, when the control signal reaches the second low state, it remains in that state regardless of changes in the output from the analog comparator 608. To make the high frequency breaker function again, the output of the circuit 502 (i.e., the output from the switched state holding circuit 608 (V)_OCb) Must be driven high. Activation of the reset switch 622 accomplishes this by: assuming that the output of the analog comparator 602 is in the first high state, the input of one of the NOR gates as discussed with reference to FIG. 6a is changed, forcing the switched state retention circuit 602 into the first high state. Notably, if the output of analog comparator 602 is low, the activation of reset switch 622 will not affect output V_OCb。

When the output V of the state holding circuit 608 is switched_OCbIn the second low state, the state is held by two particular NOR

gates

618, 620. Each of the two NOR

gates

618, 620 provides an input to the other NOR

gate

618, 620. In particular, gate 618 captures signals from gate 620A first input, and a second input influenced by the output of the analog comparator 602-e.g., output V_OCIs inverted so that: when V is_OCWhen high, the second input of gate 618 is low, and vice versa. This effect is particularly pronounced when the comparator 602 switches from its first high state to its second low state, i.e. indicating an overcurrent. Similarly, gate 620 takes a first input from gate 618 and its second input is affected by the activation of reset switch 622.

A typical waveform for the control circuit 502 is shown in fig. 6 b. At 624, from HFCT V_CTStep up the output of (a) beyond the load current reference V_OCrefIndicating an overcurrent. This will be the output V sent from gate 618, and hence from the switched state holding circuit 608_OCbThe drive is low. Referring to fig. 2a, the low output drives the and gate 220 low, then the low output of the and gate 620 is amplified by the amplifier 222 before forcing the power circuit 224 to disconnect power from the load 232. At 626, the overcurrent event stops but V_OCbRemains low until a reset is activated at 628. Another overcurrent event occurs at 630. At 632 reset is activated but to output V_OCbThere is no effect because the over current event continues until 634. Another reset activation occurs at 636 and is successful because the over current event has ceased.

Fig. 7a shows the provision of a control signal V for controlling overcurrent protection_RCDbExemplary embodiment of control circuit B (504). As discussed above, the circuit 504 is used in a High Frequency Circuit Breaker (HFCB) that includes a sensing circuit for sensing current through a load and a power circuit for connecting and disconnecting power to the load. Both circuit 502 and circuit 504 may be provided in a common HFCB, or only one may be provided. In the embodiment shown in FIG. 7a, the control circuit (or sub-circuit as the case may be) includes an OpAmp U₇(700) And a switched state holding circuit 708.

The analog comparator 706 outputs (V) from the sensing circuit_RCDct) With a current reference (V)_RCDref) A comparison is made. And switching overThe state retention circuit 708 provides a control signal to the power circuit (see 224 of fig. 2a and 224' of fig. 2 b) based on the output from the analog comparator 706 to force the power circuit to selectively connect power to the load or disconnect power to the load. Using these

circuits

706 and 708, the control circuit 504 provides a control signal for monitoring the leakage current and controlling the disconnection of the connection of power to the load when the leakage current exceeds a predetermined threshold specified by the feedback loop 702 of the comparator 706.

Component U₃(700) Is a comparator that detects leakage current. Component 700 may be a high speed comparator Integrated Circuit (IC). As shown, the component 700 is an OpAmp. The OpAmp700 is powered by VCC, and VCC also contributes to the positive feedback loop 702 of the component 700.

A positive feedback loop provides a leakage current reference. The leakage current reference comprises a variable impedance (R)₁₆-704) and an impedance (R)₁₈). Changing the impedance of the variable impedance 704 adjusts the leakage current reference.

A leakage current reference is applied at the positive terminal of the OpAmp700 and a sensed leakage current is applied at the negative terminal of the OpAmp 700. Thus, if the leakage current reference is greater than the sensed leakage current, the output of the OpAmp700 will be high and the circuit 504 will operate normally. If the leakage current reference is at least as large as the sensed leakage current, the output of the OpAmp700 will be low and the leakage current protection triggered.

The output of the comparator circuit 706 is delivered to a switching state holding circuit 708. If the output of the comparator circuit 706 is high, the switching state holding circuit 708 shown in FIG. 7a will hold the high output (V)_RCDb). If the output of the comparator circuit 706 is low, the switched state holding circuit 708 shown in FIG. 7a will switch to a low output (V)_RCDb)。

Referring to the embodiment shown in fig. 2a and 2b, the circuit 504 includes the comparator 206. Thus, output (V)_RCDb) From comparator 206 to and gate 220. Thus, the high output from comparator 206 will make the state of the AND gate dependent on its other inputs. Conversely, the low from comparator 206 pulls the AND gate output low.This low output will cause the power circuit 224, 224' to disconnect power to the load 232.

Ideally, the switching state retention circuit 708 should maintain a low output when a leakage current event is experienced to ensure that the circuit does not resume normal operation until the leakage current event is resolved. To facilitate state retention, e.g., to maintain a low output when a leakage current event is experienced, switched state retention circuit 708 includes a NOR (NOR) circuit similar to that of circuit 502. NOR function pass-through unit U₈(710) And U₉(712) To be implemented. These components 710, 712 may be Complementary Metal Oxide Semiconductor (CMOS) NOR gate ICs.

To provide a NOR gate input that is sufficiently persistent to facilitate switching, the switching state retention circuit 708 includes a hysteresis block or hysteresis component U₁₀(614). The hysteresis component 714 has the same characteristics with respect to leakage current as those described with respect to the hysteresis component 614 for overcurrent and operates with the same functions as those described with respect to the hysteresis component 614 for overcurrent.

The hysteresis component 714 is used to control the indicator Lamp₂(Lamp)₂)(716). When there is no over-current, the lamp ₂716 are not bright. On the contrary, when overcurrent occurs, the lamp ₂716 light up.

If the output voltage (V) of the HFLCT (see, e.g., reference numeral 330 in FIG. 3 a) or the DCLCT (see, e.g., reference numeral 332 in FIG. 3 b)_RCDct) Less than leakage current reference (V)_RCDref) Then the output voltage (V) of the comparator 702_RCD) Is high. Due to V_RCDHigh, output (V) of block 708_RCDb) Is high. Thus, the indicator Lamp₂(Lamp)₂) Not bright. In other words, the outputs from the analog comparator 706 and the switched state holding circuit 708 may have multiple states, now two states each, which are implemented by the HFLCT and reset switch 722 in the same manner as described above with respect to the HFCT and reset switch 622 affecting the outputs of the comparator 606 and the switched state holding circuit 608.

When the output V of the holding circuit 708 is switched_RCDbIn the second low stateThis state is maintained by two specific NOR gates 718, 720. The operation of NOR gates 718, 720 is the same as the operation of NOR

gates

618, 620.

A typical waveform for the control circuit 504 is shown in fig. 7 b. At 724 from HFLCT V_RCDctStep up the output of (a) beyond the load current reference V_RCDrefIndicating unacceptably high leakage current. This will be the output V sent from gate 718_RCDb-the output V_RCDbAlso from the switched state holding circuit 708-is driven low. Referring to fig. 2a, the low output drives the and gate 220 low, then the low output of the and gate 620 is amplified by the amplifier 222 before forcing the power circuit 224 to disconnect power from the load 232. At 726, the leakage current event stops but V_RCDbRemains low until a reset is activated at 728. Another leakage current event occurs at 730. Reset is enabled at 732 but on output V_RCDbThere is no effect because the leakage current event continues until 734. Another reset activation occurs at 736 and is successful because the leakage current event has ceased.

Also shown in fig. 7a is a test circuit 738. The circuit 738 is used to check the effectiveness of the leakage current protection provided by the circuit 504. At the activation of the button S_tA leakage current of a specified value occurs, causing a voltage across resistor R₁₄Terminal T₁And terminal T₂Current leakage therebetween. Terminal T of test circuit₁、T₂The active (live) and return terminals are connected across the HFLCT or DCLCT, see, e.g., HFLCT330 in fig. 3a and DCLCT 332 in fig. 3 b. In a successful test, the current leakage across circuit 738 will be V_RCDctPulls low and causes the indicator Lamp₂(Lamp)₂) And (4) lighting up.

The control circuit 506 as shown in fig. 8a may provide an and gate function (see 220 in fig. 2a and 2 b) and an amplification function (see 222 in fig. 2a and 2 b). It is noted that the circuit 506 may be easily modified to not include one of these functions if allowed by the design of the HFCB.

The control circuit 506 implements the start (S) of HFRCCBO_ON) -providing for startingInput or Start input-and stopping of HFRCCBO (S)_OFF). The circuit 506 may generate a synchronization signal (V) for an electrical switch_P1And V_N1). The circuit 506 may additionally or alternatively generate a drive voltage (G) for both switching components 312, 314_p-S_pAnd G_n-S_n). The circuit 506 may additionally or alternatively generate drive voltages (R _ a-R _ B) to the control coil 304 of the relay 302.

V_P1Is a synchronous signal of a positive high frequency supply voltage applied to terminal AC _ IN1(800), and V_N1Is a synchronization signal of the negative high frequency supply voltage applied to the terminal AC _ IN2(802), where the terminals AC _ IN1 and AC _ IN2 are connected to the high frequency AC power source — see e.g. label 340 of fig. 3 a.

Component U₁₁(804)、U₁₂(806)、U₁₄(808) And U₁₅(810) Is used to isolate the input from the output and may be a high speed optical coupler. Component U₁₃(812) Providing the same function. Component 812 may be a CMOS and gate IC.

Component U₁₆(814) And U₁₇(816) A drive voltage is generated that is used by the power circuit to connect (including maintain) and disconnect power to the load. Component 814 provides the drive voltage to the switching component of the power circuit, and component 816 provides the drive voltage to the relay component of the power circuit, i.e., the control coil. The components 814, 816 are thus high speed drivers for applications requiring low current digital signals to drive large capacitive loads, such as the power switching components mentioned above. In order to enable low current signals to drive large loads, OpAmp is used. Component 814 can include a pair of OpAmps, one for each control signal. Similarly, the component 816 comprises an OpAmp for amplifying the control signal of the control coil of the relay, and external power supplies (VCC, GND).

Component 814 is used to amplify both control signals. The control signal is used as a drive voltage to the two switching means 312, 314 shown in fig. 3a and 3 b. The number of signals amplified by block 814 will depend on the number of switching blocks used in the HFCB. Similarly, in some embodiments, a single output may be used to drive multiple switching components. However, in the present case, the switching components operate 180 ° out of phase and therefore require separate signal sources.

The circuit 506 comprises a voltage matching device, a component U₁₈(818) For converting the external supply voltage VCC to an isolation voltage for matching with the supply voltage of the component 814. Currently, component 818 is a DC-DC converter.

Circuit 506 also includes a start button (S)_ON) Activation of the start button drives the input voltage and other inputs of the HFCB to a desired level as necessary to begin proper operation of the HFCB 822. The output V of the circuit 502 is activated without overcurrent protection and leakage current protection_OCbV of the sum circuit 504_RCDbIs high. Indicator Lamp₃(Lamp)₃)820 are lit. Upon depression of the start button 822, a drive voltage V is provided across terminals R _ A, R _ B (824)_RABTo activate the control coil (R _ a-R _ B) of the relay. Thus, the contacts (R _7-R _4 and R _9-R _6) of the relay are closed. This bypasses the switch 822 and maintains the operation of the relay.

At the same time, component 814 outputs a drive voltage to a switch (e.g., label 310 of fig. 3a and 3 b). The switching components (e.g., transistors 312, 314) that are activated by the drive voltage will depend on when the button 822 is pressed during the AC cycle.

A stop button 826 (S) is also provided_OFF) To stop the operation of the HFCB. When button 826 is activated, power to the drive voltage VCC is disconnected. Indicator (Lamp)₃) Thus turned off, and a driving voltage (V) supplied to a control coil of the relay_RAB) Becomes zero. Thus, the contacts (R _7-R _4 and R _9-R _6) are open.

At the same time, to M_pDriving voltage (V) of_Gp) And to M_nDriving voltage (V) of_Gn) Becomes zero. Thus, referring to fig. 3a, both the relay 302 and the switch 310 are open, thereby disconnecting power to the load 342.

Similarly, if V_OCBAnd V_RCDbEither is low, this drives the outputs of components 812, 808Is low, thereby enabling the lamp ₃820 is closed. Drive voltage (V) to relays and switches_RAB) Also becomes low.

A typical waveform for the control circuit 506 is shown in fig. 8 b. Before 828, the supply voltage V_acIs sinusoidal and the terminal supplies a voltage V_P1And V_N1Providing an opposite square wave. In addition, V_OCbAnd V_RCDbHigh indicates no overcurrent or unacceptable leakage current conditions. Activation of the switch 822 at point 828 connects power to the load. This will be the voltage V across the relay_RABAnd a voltage V across the lamp_Lamp3Pulling to a high level. In addition, the gate voltages of the switched

transistors

312, 314 are powered using opposite square waves (see reference 830). At 832, stop button 826 is activated by applying a relay and gate voltage V_RAB、V_GpAnd V_GnPulling low to cut off power to the load. By pressing the start button 822, power to the load is reconnected at 834 and the HFCB trips due to one or both of the HFCT and HFLCT or DCLCT outputs going low at 836, indicating an over current event and/or a leakage current event.

The control circuit is formed using

sub-circuits

502, 504 and 506 of fig. 6a, 7a and 8a respectively, and thus the overall operation of the hfrcbo is as follows: if the sensed current signal (V) is sent from the HFCT_CT) Less than current reference (V)_OCref) Then the actual load current is less than the specified load current. Thus, the output (V) of block 610_OCb) Is high, and the lamp₁Not bright. Therefore, overcurrent protection is not activated.

If the sensed current signal (V)_CT) Not less than the current reference signal (V)_OCref) Then the actual load current is not less than the specified load current. Thus, the output (V) of block 610_OCb) Is low and indicator (light)₁) And (4) lighting. This activates overcurrent protection by pulling the and gate low, resulting in low power to the power circuit and thus disconnecting power from the load.

Similarly, if the leakage current signal (V) is sensed_RCDct) Less than the leakage current reference signal (V)_RCDref) Then the actual leakage current is less than the specified leakage current. Output (V) of block 710_RCDb) Is high, and an indicator (lamp)₂) Not bright. Therefore, the leakage current protection is not activated.

If the actual leakage current is not less than the specified leakage current, the sensed leakage current signal (V)_RCDct) Not less than the leakage current reference signal (V)_RCDref). Thus, the output (V) of block 710_RCDb) Is low and the indicator Lamp₂(Lamp)₂) And (4) lighting up. This activates leakage current protection by pulling the and gate low, resulting in low power to the power circuit, and thus disconnecting power from the load.

Indicator (light) if start button 822 is pressed₃) The driving voltage (V) that is lit and output through component 816_RAB) Is applied to the control coil (R _ A-R _ B) of the relay (Re). Thus, the contacts (R _7-R _4 and R _9-R _6) of the relay (Re) are closed. The start button 822 is bypassed by closing contacts R _7-R _4, and points P1 and P1 in the power circuit are connected by closing contacts R _9-R _ 6. Grid voltage V_GpAnd V_GnAre alternately activated to close the switches of the power circuit and high frequency AC power is applied to the load.

If stop button 826 is pressed, indicator 820 is not illuminated and the drive voltage (V) output by component 816_RAB) Is zero. Thus, the contacts R _7-R _4 and R _9-R _6 of the relay are open. This will disconnect point P1 and point P2 in the power circuit. Two driving voltages V output by the component 814_GpAnd V_GnBecomes zero and turns off

transistors

312 and 314 and

diodes

316 and 318. This disconnects point P2 and point P3 in the power circuit. Thus, the high frequency AC power source is disconnected from the load.

If an overcurrent occurs, the output (V) of block 610_OCb) Driven low, indicator lamp 616 lights up and the high frequency AC power source is disconnected from the load with each press of stop button 826. In addition, V_OCbThe output remains low and the indicator Lamp₁(Lamp)₁)616 remain on until Reset is pressed₁(reduction of position)₁)622。

The output of block 710 (V) if a leakage current event occurs_RCDb) Driven low, indicator lamp 716 lights up and the high frequency AC power source is disconnected from the load with each press of stop button 826. In addition, V_OCbThe output remains low and the indicator Lamp₁(Lamp)₁)616 remain on until Reset is pressed₁(reduction of position)₁)622. In addition, V_RCDbThe output remains low and the indicator Lamp₂(Lamp)₂)716 remain on until Reset is pressed₂(reduction of position)₂)722。

It will be appreciated that many variations and combinations of the above circuitry will be apparent to the skilled person upon reading the present disclosure. This embodiment is for illustrative purposes only, and the scope of the present disclosure may be found in the claims.

Claims

1. A control circuit for a high frequency circuit breaker, HFCB, the HFCB comprising: a sensing circuit for sensing at least one of a high frequency leakage current and a high frequency current through a load; and a power circuit for connecting and disconnecting power to the load; the control circuit includes:

a switching state holding circuit for providing a control signal to the power circuit based on the output of the analog comparator to force the power circuit to selectively connect or disconnect power to the load;

the output from the analog comparator has a first state indicating that the output from the sensing circuit does not exceed the current reference and a second state indicating that the output from the sensing circuit exceeds the current reference;

the control signal from the switching state retention circuit has a first control state for forcing the power circuit to connect power to the load and a second control state for forcing the power circuit to disconnect power to the load;

upon switching the output from the analog comparator from the first state to the second state, switching a control signal from the first control state to the second control state;

in the event that the control signal reaches a second control state, the control signal remains in the second control state regardless of changes in the output from the analog comparator;

the control circuit further comprises a reset switch, activation of which forces the switched state retention circuit into a first state if the output of the analog comparator is in the first state;

the switching state holding circuit includes a NOR circuit including a plurality of NOR gates and an inverter circuit including a plurality of inverters;

two of the plurality of NOR gates are used to hold the second state of the switched state holding circuit, and:

each of the two NOR gates providing an input to the other NOR gate;

the inputs of the two NOR gates are affected by the activation of the reset switch; and

the input of the other of the two NOR gates is affected by the change in the output of the analog comparator from the first state to the second state.

2. The control circuit of claim 1, wherein the output of the analog comparator is based on a difference between the output from the sensing circuit and the current reference.

3. The control circuit of claim 1 or 2, wherein the output from the sensing circuit comprises a voltage, the current reference comprises a voltage indicative of a threshold current, and the analog comparator identifies a voltage difference.

4. The control circuit of claim 1, wherein the analog comparator comprises a high speed comparator Integrated Circuit (IC).

5. The control circuit of claim 1, wherein the analog comparator includes a differential operational amplifier (OpAmp) for determining a difference between the output from the sensing circuit and the current reference.

6. The control circuit of claim 5, wherein the OpAmp and the current reference are driven by a common Direct Current (DC) input voltage.

7. The control circuit of claim 1, wherein the current reference comprises a variable impedance and an impedance, and changing the impedance of the variable impedance adjusts the current reference.

8. The control circuit of claim 1, wherein the control signal maintains the second state regardless of changes in the output from the analog comparator if the control signal reaches the second state.

9. The control circuit of claim 1, wherein the control circuit is to receive an output from a sensing circuit, the sensing circuit comprising:

The control circuit includes:

a first sub-circuit, comprising:

a comparator as a first comparator for comparing an output from the first high frequency current transducer with a respective load current reference or leakage current reference; and

the switching state holding circuit as a first switching state holding circuit; and

a second sub-circuit, comprising:

a second analog comparator for comparing an output from the second high frequency current transducer with a respective load current reference or leakage current reference; and

a second switching state holding circuit for providing a control signal to the power circuit based on an output from the second analog comparator to force the power circuit to selectively connect or disconnect power to the load.

10. A high frequency circuit breaker, HFCB, comprising:

a control circuit;

a power circuit for connecting and disconnecting power to the load,

wherein the control circuit comprises:

a switched state retention circuit for providing a control signal to the power circuit based on the output from the analog comparator to force the power circuit to selectively connect or disconnect power to the load;

each of the two NOR gates providing an input to the other NOR gate;

11. The high frequency circuit breaker HFCB of claim 10, wherein the power circuit comprises relays and switches, each of which is switchable between an on state and an off state.

12. The high frequency circuit breaker HFCB of claim 11, wherein the relay and switch are connected in series such that: if any of the relay and the switch is switched to the off state, the connection of the power to the load is disconnected.

13. The high frequency circuit breaker HFCB of claim 11, wherein the relay and switch are connected in parallel such that: once either one of the relay and the switch is switched to the on state, power is connected to the load.

14. High frequency circuit breaker HFCB according to any of the claims 10-13, wherein the sensing circuit comprises two AC-DC rectifiers and a DC residual current transducer.

15. The high frequency circuit breaker HFCB of claim 14, wherein the power circuit comprises two outputs, the load comprises two terminals, and the AC-DC rectifiers each comprise an input, wherein:

one output of the power circuit and one terminal of the load provide an AC input to one of the two AC-DC rectifiers; and is

The other output of the power circuit and the other terminal of the load provide the other AC input to the other of the two AC-DC rectifiers.

16. The HFCB of claim 14, wherein each AC-DC rectifier includes a DC output and the difference between the DC outputs provides an input to the DC residual current transducer and the output of the DC residual current transducer is isolated from the input of the DC residual current transducer.