GB2526908A

GB2526908A - Residual current protection device

Info

Publication number: GB2526908A
Application number: GB1505322.6A
Authority: GB
Inventors: hua lei Liu; xiao mei Wang; Lin Yang
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2014-04-30
Filing date: 2015-03-27
Publication date: 2015-12-09
Anticipated expiration: 2035-03-27
Also published as: CN105098705A; AU2015201523A1; AU2015201523B2; GB201505322D0; GB2526908B; CN105098705B

Abstract

A residual current protection device comprises a leakage detection circuit, a trigger circuit M3 and a voltage stabilizing circuit M5 providing a stable supply voltage Vcc to the leakage detection circuit, the stabilization circuit M5 having a capacitor C2 for storing electrical energy and providing a voltage Vcc and a charging control circuit M51 that causes the power line L to charge the capacitor C2 when Vcc is equal to or less than a predetermined threshold and stops the charging when Vcc exceeds the threshold. The charging control circuit M51 may comprise a controlled switch Q1 in series with the capacitor C2 and a voltage clamping element D5, wherein the switch Q1 is turned on when the voltage difference between the clamping element D5 and the capacitor C2 exceeds its turn-on voltage. The switch Q1 may be a MOS transistor and the clamping element D5 may be a zener diode, the cathode of which may be connected to the gate of the switch Q1. The turn-on voltage of the clamping element D5 may be higher than that of the switch Q1.

Description

Residual current protection device

Technical field

The present invention relates to a residual current protection device (RCD) , in particular to a voltage stabilizing circuit in au RCD.

Background art

An RCD is a widely used circuit protection device, used to instruct a circuit breaker S to cut off the power supply to an electrical appliance when an appliance develops a current leakage fault, in order to prevent electrocution. An RCD in the prior art has the structure shown in Fig. 1, comprising: a rectification circuit 1, a surge protection circuit 2, a trigger circuit 3, an overvoltage protection circuit 4, a voltage stabilizing circuit 5, a leakage detection circuit 6, a current sampling circuit 7, and a current transformer (transformer for short) ZCT. The rectification circuit 1 is connected to a phase line L, a neutral line N and a protective earth line FE of a power distribution system, and used to rectify an input current. The surge protection circuit 2 is used to provide surge protection for the circuit of the RCD.

The trigger circuit 3 is used to provide a trip signal to a circuit breaker 5, so that the circuit breaker S opens to prevent electrocution. The overvoltage protection circuit 4 is used to provide overvoltage protection for the circuit of the RCD, preventing components in subsequent circuits from being damaged by overvoltage. The voltage stabilizing circuit 5 provides a stable power supply voltage Vcc to the leakage detection circuit 6 after receiving electrical energy from the overvoltage protection circuit 4. The current sampling circuit 7 is connected to a sampling coil of the transformer ZOT. When a leakage current occurs, an induced current will be generated in the sampling coil of the transformer ZCT; the current sampling circuit 7 can receive the induced current and cutput a signal to the leakage detection circuit 6 according to the induced current received. After receiving the signal from the current sampling circuit 7, the leakage detection circuit 6 provides a leakage protection trigger signal Strgger to the trigger circuit 3, so that the trigger circuit 3 provides a trip signal to the circuit breaker S. thereby making the circuit breaker S open to prevent electrocution.

The voltage stabilizing circuit 5 provides a power supply voltage Vcc to the leakage detection circuit 6. If the power supply voltage Vcc is not stable, it will be very difficult to ensure normal operation of the leakage detection circuit 6.

Therefore the voltage stabilizing circuit 5 plays a vital role in the RCD. For example, the Mitsubishi M54123 is used as a detection chip in the leakage detection circuit of many RCDs on the market. According to the requirements described in the specification booklet for that product, the power supply voltage of the chip is preferably about 15 V, and cannot be less than 12 V. When the power supply voltage Vcc is less than 12 V, the internal latch of the chip will be disconnected, and the circuit of the chip will stop working, causing the RCD to fail. Thus, the design of the voltage stabilizing circuit 5 is key to the entire RCD circuit.

In most existing RCDs, an RC scheme is employed to form the voltage stabilizing circuit, i.e. voltage stabilization is achieved by using a large resistor for voltage reduction and a large capacitor for charging and discharging, to ensure that a stable power supply is provided to the detection chip in the leakage detection circuit 6. However, as the reguirements on RCD performance have increased, the need has arisen to find another type of voltage stabilizing circuit, that is capable of providing, to an RCD and in particular a leakage detection chip, a stable power supply that meets the operating requirements thereof.

Content of the invention The object of the present invention is to provide an ROD, a voltage stabilizing circuit of which can provide a stable power supply to a leakage detection chip continuously for a predetermined time even when the N line is damaged.

The present invention provides an ROD, comprising: a leakage detection circuit, for outputting a leakage protection trigger signal when a leakage current occurs on a power supply line; a trigger circuit, which is connected to the leakage detection circuit and outputs a trip signal in response to the leakage protection trigger signal, the trip signal being capable of instructing a circuit breaker connected to the power supply line to break a power supply connection; a voltage stabilizing circuit which provides a stable power sllpply voltage to the leakage detection circuit, the power supply voltage being greater than or egual to a voltage reguired for operation of the leakage detection circuit; wherein the voltage stabilizing circuit comprises: an energy storage capacitor, for storing electrical energy and providing the power supply voltage; a charging control circuit connected between the power supply line and the energy storage capacitor, wherein the charging control circuit causes the power supply line to charge the energy storage capacitor when the voltage on the energy storage capacitor is egual to or less than a predetermined threshold, and cuts off charging of the energy storage capacitor when the voltage on the energy storage capacitor is greater than the predetermined threshold.

In the ROD provided by the present invention, the power supply voltage Vcc provided by the voltage stabilizing circuit thereof can rise quickly and stay at the operating voltage required by the detection chip. Compared with the existing RC scheme, the voltage stabilizing circuit proposed in the present invention has a short power-on time, and can reach a stable power supply voltage Vcc in a comparatively short time.

In an ROD provided according to the present invention, the charging control circuit comprises a controlled switch and a voltage clamping element; the controlled switch is connected in series with the energy storage capacitor, and charging of the energy storage capacitor takes place when the controlled switch is turned on; when the difference between the voltage on the voltage clamping element and the voltage on the energy storage capacitor exceeds a turn-on voltage of the controlled switch, the controlled switch is turned on, otherwise the controlled switch is turned off.

For example, when the N line is damaged, it is necessary to ensure that the current flowing through the FE line is less than 2 mA; in order to meet this requirement, an existing RO scheme must increase the resistance of the vcltage-reducing resistor therein. However, in order to enable a product to operate normally at a lower voltage, it is also necessary to reduce the resistance of the resistor in the RO scheme.

Compared to the RC scheme, the circuit proposed in the present invention can overcome this problem very well.

Furthermore, in an ROD provided according to the present invention, the controlled switch is a MOS transistor, the voltage clamping element is a Zener diode, and the gate of the controlled switch is connected to the cathode of the Zener diode, while the source of the controlled switch is connected to an output voltage end of the energy storage capacitor.

In an ROD provided according to the present invention, a turn-on voltage of the voltage clamping element is larger than the turn-on voltage of the controlled switch.

The ROD provided according to the present invention further comprises a current-limiting resistor connected between the gate and drain of the controlled switch.

The ROD provided according to the present invention further comprises a second Zener diode; a positive terminal thereof is connected to the output voltage end of the energy storage capacitor, a negative terminal thereof is connected to the gate of the controlled switch, and the breakdown voltage thereof is less than the gate-source breakdown voltage of the controlled switch.

The ROD provided according to the present invention further comprises a rectification circuit for providing a voltage from the power supply line to the voltage stabilizing circuit after rectification.

In the ROD provided according to the present invention, the rectification circuit is a half-bridge rectification circuit.

The ROD provided according to the present invention further comprises an overvoltage protection circuit comprising a resistor and a Zener diode.

In the ROD provided by the present invention, the power supply voltage Vcc provided by the voltage stabilizing circuit thereof can rise quickly.

Description of the accompanying drawings

The following accompanying drawings are merely intended to illustrate and explain the present invention schematically, without defining the scope thereof.

Fig. 1 shows a structural schematic diagram of an ROD in the

prior art;

Fig. 2 shows a schematic diagram cf the circuit structure of an ROD according to am embodiment of the present invention.

Particular embodiments Fig. 2 shows by way of example an ROD according to an embodiment of the present invention. In Fig. 2, similarly to Fig. 1, the ROD comprises & rectification circuit Ml, & surge protection circuit M2, a trigger circuit M3, an overvoltage protection circuit M4 and a voltage stabilizing circuit M5, a sampling circuit and a leakage detection circuit (the last two are the same as in Fig. 1, and are not shown in Fig. 2) As Fig. 2 shows, the rectification circuit Ml preferably comprises a half-bridge rectification bridge formed by diodes D6, D7, D8, D9 and DlO. The rectification circuit Ml is connected to a phase line L, a neutral line N and a protective earth line FE in a power supply line of a power distribution system, and used to perform half-wave rectification of current from the power supply line. Optionally, the rectification circuit Ml may also be a full-bridge rectification circuit.

The surge protection circuit M2 is used to prevent a surge current from damaging subsequent circuits. In the example of Fig. 2, the surge protection circuit M2 comprises varistors ES and R4. The varistors R3 and R4 clamp the potential to a relatively fixed voltage value, thereby protecting circuits in later stages.

Similarly to Fig. 1, the trigger circuit M3 in Fig. 2 receives a trigger signal 0 from the leakage detection circuit, and generates a trip signal in response to the trigger signal, to instruct a circuit breaker S connected in the power supply line to open. In the specific example of Fig. 2, the trigger circuit M3 comprises a thyristcr Q2, the controlled terminal G of which is connected to the leakage detection circuit. When the le&kage detection circuit detects a leakage current, the controlled terminal G of the thyristor receives a valid HIGH level, and causes Q2 to conduct. Now that Q2 is conducting, the current flowing in the phase line L and neutral line N increases sharply, and this drives the circuit breaker S to execute an opening action. Preferably, in view of the fact that the thyristor Q2 is quite sensitive to external point noise signals and is easily triggered erroneously, a capacitor Cl is connected between the controlled terminal G of the thyristor and ground in the example of Fig. 2. When the controlled terminal C of the thyristor Q2 receives a valid HIGH level, Q2 will not immediately begin to conduct; instead, the HIGH level C will charge the capacitor Cl. Only when the capacitor Cl has charged to the voltage at which the thyristor Q2 begins to conduct, will Q2 begin to conduct. Thus, the provision of the capacitor Cl can filter out high-frequency noise, preventing erroneous triggering of Q2.

The overvoltage protection circuit M4 in Fig. 2 comprises a resistor Ri and a Zener diode D3. The resistor Ri is connected in series in the pathway on which the phase line L is located, and has the effect of reducing voltage. The Zener diode P3 has its two ends connected in parallel between the voltage-reduced phase line L and the neutral line N, and has the effect of stabilizing voltage. In other words, when the voltage between P and N after rectification and voltage reduction exceeds the breakdown voltage of the Zener diode, reverse breakdown of the Zener diode occurs, and the voltage across the Zener diode remains at a predetermined value. Thus, through the voltage-reducing effect of the resistor Rl and the voltage-stabilizing effect of the Zener diode P3, the overvoltage protection circuit M4 can prevent components in subsequent circuits from being damaged by overvoltage.

The voltage stabilizing circuit ME in Fig. 2 is no longer a conventional RC voltage stabilizing circuit, but a low-voltage voltage stabilizing circuit. As Fig. 2 shows, the voltage stabilizing circuit M5 preferably comprises an energy storage capacitor 02 and a charging control circuit M51. The energy storage capacitor 02 is used for storing electrical energy, and provides a power supply voltage Vco to a chip in, for example, a leakage detection cirouit. On the one hand, the charging control circuit M51 detects whether the voltage on the capacitor 02 has reached a predetermined voltage (e.g. 15 V) On the other hand, the charging control circuit M51 charges the capacitor 02 when the voltage on the capacitor 02 is less than the predetermined voltage, otherwise it stops charging. In other words, the charging control cirouit oauses the power supply line to oharge the energy storage oapacitor 02 when the voltage Vcc on the energy storage capacitor 02 is egual to or less than a predetermined threshold Vd (e.g. 15 V), and cuts off the charging of the energy storage capacitor 02 when the voltage Vcc on the energy storage capacitor 02 is greater than the predetermined threshold Vd.

In one embodiment, the charging control circuit M51 comprises a controlled switch Q1. Ql is coupled between the power supply line P and the energy storage capacitor 02. In the example of Fig. 2, Q1 is an N-type MOS transistor, the drain of which is connected to an output end of the overvoltage protection circuit M4, i.e. resistor Ri. The source of Qi is connected to a voltage output end Vcc of the capacitor 02. A Zener diode D5 is oonnected between the gate of Q1 and ground. The Zener diode provides a reference voltage for the gate. Suppose that the turn-on voltage of Qi is 4 V, and the desired voltage of Vcc is V; then 55 can be a Zener diode with a clamping voltage of 19 V. Preferably, a current-limiting resistor R2 is further connected between the gate and drain of Q1, to prevent damage to Qi by large currents. More preferably, a Zener diode 54 with a breakdown voltage less than the gate-source breakdown voltage of Ql is further connected between the source and gate of Q1, preventing breakdown of the MOS transistor, to provide a voltage stabilization protection function.

In Fig. 2, in an initial state Qi is turned off and there is no voltage on the capacitor 02. After powering on, current from the power supply line undergoes rectification, surge protection and overvoltage protection before being applied to the voltage stabilizing circuit MS. As Fig. 2 shows, when the voltage applied to MS has increased to a level capable of turning on Zener diode 55, Zener diode 55 begins to conduct, and current flows through the current-limiting resistor R2 and the turned-on Zener diode D5. Zener diode 55 clamps the voltage between its two ends at 19 V, i.e. the gate voltage of Qi is clamped at 19 V. At this time, because the voltage on 02 is approximately zero, the voltage between the gate and source of the MOS transistor Qi is larger than the turn-on voltage 4 V thereof, so the MOS transistor begins to conduct, the capacitor 02 is charged, and Vcc gradually increases. Since the resistance of the MOS transistor Qi when conducting is very small, the current which charges the capacitor 02 is very large, and it takes a very short time for the voltage on capacitor 02 to rise. When Vcc increases to 15 V, the voltage difference between the gate and source of the MOS transistor Q1 is egual to or slightly less than 4 V, so that the MOS transistor Qi turns off, at which point the capacitor 02 switches from charging to discharging, keeping Vcc close to 15 V. When Vcc falls below 15 V, the voltage difference between the gate and source of the MOS transistor Ql is again larger than the turn-on voltage 4 V, the MOS transistor Q1 begins to conduct, and the capacitor 02 begins charging again, causing Vcc to rise. As this cycle is repeated, Vcc can be stabilized at about 15 V. Furthermore, when the half-wave voltage is on a falling edge and causes Vcc to fall, the capacitor 02 can also keep Vcc at about 15 V by discharging. In this way, the voltage stabilizing circuit provides a stable power supply to the detection chip in the leakage detection circuit.

In the voltage stabilizing circuit provided in this embodiment, Vcc can rise quickly, so that the time taken for the ROD to reach a stable state is short; moreover, the stable-state -10 -operating current is small, power consumption is low, and voltage ripples and noise are low.

With regard to an RCD employing the voltage stabilizing circuit provided in this embodiment, since a stable power supply to the detection chip can be guaranteed, when the voltage of L with respect to N is 85 V and a 5 Idn leakage current is suddenly applied, the action time can be less than 40 ms; when the voltage of L with respect to N is 380 V, the system can operate stably for at least 1 hour; the stable-state operating current is less than 1 mA under normal conditions, and less than 2 mA when the N line is damaged; when the N line is damaged, the L to FE circuit resistance is Rx = 2 Q, and when the voltage is 0.85*LJn and there is a 5 Idn leakage current, the action time is less than 40 ms. Thus, the RCD proposed in the present invention can fully satisfy all new performance requirements for RCDs at the present time.

In the embodiments above, the voltage stabilizing circuit of the present invention is explained using the abovementioned specific parameters as an example, but these paramerers are by no means restrictive, and those skilled in the art could choose other component parameters depending on the required Vcc.

According to another embodiment of the present invention, the MOS transistor may also be replaced by another switch, e.g. a bipolar junction transistor, etc.; those skilled in the art could make various selections according to actual requirements.

According to another embodiment of the present invention, the rectification circuit may also be a full-bridge rectification circuit, which performs full-wave rectification of an input voltage.

It should be understood that although the description herein is based on various embodiments, it is by no means the case that each embodiment contains just one independent technical -11 -solution. Such a method of presentation is adopted herein purely for the sake of clarity. Those skilled in the art should consider the description in its entirety. The technical solutions in the various embodiments could also be suitably corrbined to form other errbodiments capable of being understood by those skilled in the art.

The above embodiments are merely particular schematic embodiments of the present invention, which are not intended to define the scope thereof. Any eguivalent changes, modifications or combinations made by those skilled in the art without departing from the concept and principles of the present invention should be included in the scope of protection thereof.