Circuit and method for recirculating a current

Abstract

 The present invention relates to a circuit for passing AC or DC power from a power source to a connected load, the circuit comprising a main switch for connecting/disconnecting the load to/from the power source, a first current path for recirculating a current in a first direction when the load is disconnected from the power source, and a second current path for recirculating a current in a second direction when the load is disconnected from the power source. The present invention further relates to an associated method for recirculating a current.

Description

FIELD OF THE I NVENTI ON

[0001] The present invention relates to a circuit and an associated method for automatic recirculation of currents within said circuit. I n particular the present invention facilitates that pulse width modulated (PWM) currents, DC currents with any polarity as well as AC currents may be recirculated in an automatic manner when the load is disconnected from the power source.

BACKGROUND OF THE I NVENTI ON

[0002] Recirculation of AC currents in circuits including inductive loads is known to be complicated. I n particular, recirculation of AC currents and recirculation of DC currents with both positive and negative polarities is complicated.

[0003] US 6,670,792 discloses how a DC current with the help of a traditional diode may be recirculated. However, the arrangement presented in US 6,670,792 only allows that DC currents originating from a voltage of a certain polarity may be recirculated. A current driven by a voltage of the opposite polarity may not be recirculated.

[0004] WO 2012/021072 shows an arrangement where AC current may be recirculated by sequentially shunting diodes in the positive and the negative half periods. Controllable switches are applied for shunting the diodes. The arrangement suggested in WO 2012/021072 appears to be a complicated and expensive arrangement.

[0005] It may be seen as an object of embodiments of the present invention to provide a circuit and an associated method for recirculating a current within said circuit.

[0006] It may be seen as a further object of embodiments of the present invention to provide a circuit and an associated method for recirculation of DC, AC or PWM currents.

[0007] It may be seen as an even further object of embodiments of the present invention to provide a circuit and an associated method where recirculation is performed automatically.

DESCRIPTI ON OF THE I NVENTI ON

[0008] The above-mentioned object are complied with by providing, in a first aspect, a circuit for passing AC or DC power from a power source to a connected load, the circuit comprising

• a main switch for connecting/disconnecting the load to/from the power source,
• a first current path for recirculating a current in a first direction when the load is disconnected from the power source, and
• a second current path for recirculating a current in a second direction when the load is disconnected from the power source

wherein the first and second current paths are implemented in a manner so that recirculation of a current is performed in an automatic way.

[0009] Thus, when the main switch is closed power may be delivered from the power source to the load. Similarly, when the main switch is open the load is disconnected from the power source. The power source may in principle be any kind of power source including all sorts of AC and DC power source. Optionally a PWM circuit may be applied to modulate the output of the power source.

[0010] The first current path may comprise a NPN type switch and a diode arranged to conduct in the first direction. Similarly, the second current path may comprise a PNP type switch and a diode arranged to conduct in the second direction. The first and second direction may, at least through the load, be opposite current directions.

[0011] It is an advantage of the present invention that either the first or the second current path is activated automatically immediately after the main switch is opened. The direction of the current in the load determines which of the two recirculating current paths to be activated. It is advantageous that no specific and dedicated actions need to be taken in order to activate a given recirculation path. The activation is performed automatically.

[0012] The NPN and the PNP switches may be connected to the power source via respective gate resistors.

[0013] At least part of the first and second current paths may be arranged in parallel. Thus, the NPN type switch and the PNP type switch may be arranged in parallel to each other, and furthermore they may be arranged in parallel over the load.

[0014] In a second aspect, the present invention relates to a power supply unit comprising a circuit according to the first aspect.

[0015] In a third aspect the present invention relates to a method for automatic recirculating AC or DC power within a circuit comprising a power source and a load connectable thereto, the method comprising the steps of

• disconnecting the load from the power source,
• recirculating a current in a first direction along a first current path in case of a first voltage polarity across the load, or
• recirculating a current in a second direction in a second current path in case of a second voltage polarity across the load.

[0016] As previously disclosed the load is disconnected from the power source by opening a main switch in the form of a controllable switch.

[0017] Again, it is advantageous that either the first or the second current path is activated automatically immediately after the main switch is opened, i.e. immediately after the load has been disconnected from the power source. Thus, it is advantageous that no specific and dedicated actions need to be taken in order to activate a given recirculation path.

[0018] The first current path may comprise a NPN type switch and a diode arranged to conduct in the first direction. The second current path may comprise a PNP type switch and a diode arranged to conduct in the second direction. The NPN type switch and the PNP type switch may be arranged in parallel over the load.

BRI EF DESCRI PTI ON OF THE DRAWINGS

[0019] The present invention will now be described in further details with reference to the accompanying figures, where

Fig. 1 shows how power is fed to the load, and

Fig. 2 shows how current is recirculated when the load is disconnected from the power source.

[0020] While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of examples in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAI LED DESCRI PTI ON OF THE I NVENTI ON

[0021] In its most general aspect the present invention relates to a circuit and an associated method for recirculating a current within said circuit in an automatic manner. The circuit comprises a power source and a load connectable thereto. The current recirculation is a consequence of the load being abruptly disconnected from the power source.

[0022] It is an advantage of the present invention that the circuit is operable with both AC and DC power sources. I n case of a DC power source the polarity of the power source voltage is of no importance. Also, pulse width modulated power source voltages may be applied to the load as well.

[0023] The load may in principle be any kind of load, such as a resistive, an inductive or a capacitive load. In case of an inductive load the associated inductive current must be recirculated when the load is disconnected from the power source.

[0024] Referring now to Fig. 1 a circuit 100 according to an embodiment of the present invention is depicted. As seen in Fig. 1 a power source 101 is connected to a load 102 via a closed switch 103. The circuit 100 depicted in Fig. 1 is designed to be operated at 24 V AC. However, the power source may deliver AC or DC power having different voltage levels, such as voltage levels up to around 220 V. Moreover, the polarities of DC power sources are arbitrary.

[0025] At 24 V AC the power source voltage may, without any complications, be pulse width modulated with a modulation frequency of up to 1 kHz. However, higher modulation frequencies may be applicable as well.

[0026] The circuit 100 comprises two oppositely directed recirculation paths. The first path comprises switch 107 and diode 106 whereas the second path comprises switch 105 and diode 104. Diodes 110 and 111 serve as overvoltage protection circuits for the switches 105 and 107, respectively.

[0027] The first and second recirculation paths are arranged parallel to each other and parallel to the load 1 02 as well. The gates of the switches 1 05 and 1 07 are connected to the power source 1 01 via respective gate transistors 1 09 and 1 08. The switches 1 05 and 1 07 are PNP and NPN type switches, respectively.

[0028] It is advantageous that the circuit according to the present invention is capable of biasing the correct switch (105 or 107) automatically without applying additional drive circuits. This automatic biasing of the correct switch (105 or 107) ensures that a current recirculation path is established automatically when the load is disconnected from the power source.

[0029] Fig. 2 shows how the load current, I, is automatically recirculated when the switch 203 is opened. The "plus" shown in Fig. 2 indicates the polarity of the power source voltage. In the scenario depicted in Fig. 2 the current, I, automatically recirculates in the circuit containing the load 202, the switch 207 and the positively biased diode 206. Similarly, an oppositely directed current may recirculate in the loop comprising the load 202, the switch 205 and the diode 204. Similar to Fig. 1 diodes 210 and 211 serve as overvoltage protection circuits for the switches 205 and 207, respectively.

[0030] It is an advantage of the present invention that the current starts recirculating automatically as soon as the switch 103, 203 is opened. Thus, no transistors or other types of switches are to be activated in order to allow recirculation of currents. This automatic recirculation behaviour is completely independent of the polarity and the nature (DC or AC) of the currents. Also, PWM currents may be recirculated automatically.

Claims

1. A circuit for passing AC or DC power from a power source to a connected load, the circuit comprising

- a main switch for connecting/disconnecting the load to/from the power source,

- a first current path for recirculating a current in a first direction when the load is disconnected from the power source, and

- a second current path for recirculating a current in a second direction when the load is disconnected from the power source,

wherein the first and second current paths are implemented in a manner so that recirculation of a current is performed in an automatic way.

2. A circuit according to claim 1 , further comprising means adapted to pulse width modulate power from the power source.

3. A circuit according to claim 1 or 2, wherein the first current path comprises a NPN type switch and a diode arranged to conduct in the first direction.

4. A circuit according to claim 3, wherein the second current path comprises a PNP type switch and a diode arranged to conduct in the second direction.

5. A circuit according to claim 4, wherein the gates of the NPN and the PNP switches are connected to the power source via respective gate resistors.

6. A circuit according to any of the preceding claims, wherein at least part of the first and second current paths are arranged in parallel.

7. A circuit according to claim 6, wherein the NPN type switch and the PNP type switch are arranged in parallel.

8. A circuit according to any of the preceding claims, wherein the NPN type switch and the PNP type switch are arranged in parallel over the load.

9. A circuit according to any of the preceding claims wherein the power source comprises a DC power source.

10. A circuit according to any of claims 1-8, wherein the power source comprises an AC power source.

11. A power supply unit comprising a circuit according to any of the preceding claims.

12. A method for automatic recirculating AC or DC power within a circuit comprising a power source and a load connectable thereto, the method comprising the steps of

- disconnecting the load from the power source,

- recirculating a current in a first direction along a first current path in case of a first voltage polarity across the load, or

- recirculating a current in a second direction in a second current path in case of a second voltage polarity across the load.

13. A method according to claim 12, wherein the load is disconnected from power source by opening a controllable switch.

14. A method according to claim 12 or 13, wherein first current path comprises a NPN type switch and a diode arranged to conduct in the first direction, and wherein second current path comprises a PNP type switch and a diode arranged to conduct in the second direction.

15. A method according to claim 14, wherein the NPN type switch and the PNP type switch are arranged in parallel over the load.

Drawing