WO1999031696A1

WO1999031696A1 - Electronic control circuit for a latching relay

Info

Publication number: WO1999031696A1
Application number: PCT/US1998/026181
Authority: WO
Inventors: Rolf Weber
Original assignee: Siemens Electromechanical Components, Inc.
Priority date: 1997-12-17
Filing date: 1998-12-02
Publication date: 1999-06-24

Abstract

A relay controller for an electrical device includes a bistable relay (22) and an electronic controller (20) having a plurality of switching transistors (32-38) for operating the relay (22) in response to commands. Advantageously, the controller operates the relay coil (24) only for a transition of the commands. At all other times the switching transistors (32-38) are off thereby insuring the safe and predictable operation of the relay. Preferably the controller and the relay (22) are incorporated into a common housing.

Description

ELECTRONIC CONTROL CIRCUIT FOR A LATCHING RELAY

BACKGROUND OF THE INVENTION

A. Field of Invention This invention pertains to the art of electronically controlled relays, and more particularly to an electronic control circuit used to operate a relay. The circuit insures low power consumption and a failsafe operation and is suited for automotive and other systems.

B. Description of the Prior Art Relays are electromagnetic devices which have been used in diverse control equipment almost since the beginning of the electrical age. In the last two decades, they have been replaced in many instances by all electronic switching devices. However in certain environments they are still preferred because they are economical and effective in environments with high levels of electromagnetic noise as well as hot environments (i.e., environments exceeding 100^C). Moreover relays provide better electrical isolation then their electronic counterparts.

Relays generally consist of one or more electromagnetic coils and electrical contacts which open or close when said coils are energized. Relays are available in two configurations: latching and non-latching. A latching relay is a bi-stable device because it has two stable positions (for example, ON or OFF) and requires a first command signal to change from the first position to the second, and a second distinct command to change from the second to the first position. The relay will maintain its position even after its coil(s) have been de-energized.

A non-latching relay has only a single stable position (OFF) and requires continuous power signal to its coil to stay on.

Both latching and non-latching relays have disadvantages. Non- latching relays are simple to control but require continuous power to their coils which causes heat, wastes energy and are not suitable for all control schemes. Latching relays generate less heat but require complicated control signals. OBJECTIVES AND SUMMARY OF THE INVENTION

In view of the above-disadvantages of the prior art, it is an objective of the present invention to provide a control circuit with a relay which provides a simple and fail safe operation.

A further objective is to provide an electronic control circuit which can be incorporated into the housing of a relay to thereby provide a small and reliable device.

Yet another objectives is to provide a relay control scheme which is flexible so that it can be used for a variety of applications.

A further objective is to provide a relay control circuit with very low power consumption, especially during quiescent periods.

Yet another objective is to provide a relay control circuit responsive to transitions in the commands received for the operator of the relays. A relay control circuit constructed in accordance with this invention includes a relay having a relay coil operating a contact for selectively energizing and de-energizing an electrical device. The relay coil has two positions and is selectively energized in response to commands by a controller including an electronic switch. Preferably, the controller includes a transition sensor for sensing transitions of said commands, said elective switch being responsive to said transitions. Optionally a load sensor is also included to sense the load presented by the device. If the load is excessive, the controller is activated to cut power to the device.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic diagram of an automotive system using a relay control circuit in accordance with this invention;

Figure 2 an elementary diagram of the relay control circuit of Figure 1 ; and Figure 3 shows a timing diagram for the relay control circuit of Figures

1 and 2. DETAILED DESCRIPTION OF THE INVENTION

Referring now to Figure 1 , an illustrative example of a relay control circuit constructed and arranged in accordance with this invention is now provided which may be used for example in an automobile to control an accessory device such as a windshield wiper motor, headlights, etc. It should be understood that the relay control circuit can be used to control many other types of devices as well.

In Figure 1 , a relay control circuit 10 is provided to control the operation of a device represented in Figure 1 by a load 12 in response to commands received a command line 14. For example, in an automotive environment, the command line may be connected to a mechanical or electronic switch 16 disposed on the dashboard (not shown). Current to the control circuit 10 may be limited by a resistor 18.

Relay control circuit 10 includes an electronic controller 20 and a relay 22, said relay 22 having a relay coil 24 and one or more contacts 26 operated by relay coil 24 as described below. For the sake of simplicity, a single coil 24 is shown, it being understood that a double coil may be used as well, one for each state. In Figure 1 , contact 26 is shown as an a-type or single throw double pole contact, it being understood that various other types of relay contacts may be provided as well. Preferably relay 22 is a bistable or latching relay, such as for example a VPR relay available from Siemens EC. When the command on line 14 requests that device 12 be activated, generated for example, by closing switch 16, the electronic controller 20 changes relay 24 coil to its energized or ON position. This action causes the contact 26 to close thereby providing power to the device 12. When a command is received to de-energize the device 12, for example, by opening switch 16, the electronic controller 20 applies a voltage to relay coil 24 selected to change the coil 24 to its OFF position. Contact 26 opens and the device 12 is de-energized. An optional feature of the relay control circuit 10 is that it includes a overload sensor circuit 28 for sensing an overload condition, such as a short. If the circuit 28 senses an overload, it sends an appropriate signal on line 30 to the electronic controller 20 which in response causes the relay 22 to change to its off position. Thus, in effect, the relay control circuit 10 may be used as an automatic fuse.

Referring now to Figure 2, the electronic control circuit 20 includes an H-bridge consisting of transistors 32, 34, 36 and 38. The transistors 32-38 are controlled by two input lines 40 and 42, and under quiescent conditions, all these transistors are off. Relay coil 24 is either in its ON or OFF position depending on the last command received by the electronic controller 20.

Input line 40 is connected to the collector of transistor 44. The base of transistor 44 is connected to a serial RC network formed of resistors 46 and 48 and capacitor 50.

Similarly input line 42 is connected to the collector of transistor 52. The base of the transistor 52 is connected to a parallel RC network formed of resistors 54, 56 and capacitor 58. Both RC networks are also connected to the command line 14 as well as line 30 and act as timers, as described below.

The electronic controller 20 operates as follows. Assuming first that switch 16 is open, the line 14 is floating and the resistors 46, 48, 54, 56 cooperate to bias transistor 44 off and transistor 52 off. Therefore the input lines 40 and 42 are high. When input line 40 is high, transistors 32 and 34 are off. Similarly, a high voltage on line 42 insures that transistors 36 and 38 are off.

When switch 16 is closed, at t=T1 (see Figure 3) the voltage at the base of transistor 52 goes low turning transistor 52 on. Therefore input line 42 goes low, as shown in Figure 3 causing transistors 36 and 38 to turn on. Transistor 38 therefore applies power to the positive terminal (24+) of relay coil 24 while transistor 36 grounds the other terminal (24-) of the relay coil 24. Therefore coil 24 changes to its ON position.

When the command line 14 goes high (at t=T1), the capacitor 58 (which previously was discharged) starts charging up causing the voltage on the base of transistor 52 to decay. The capacitor 58 and resistors 54 and 56 are selected so that after about 50 ms the voltage at the base of transistor 52 decays sufficiently to turn off transistor 52 . Therefore at T1+50 ms transistor 52 turns off, line 42 goes high, thereby turning transistors 36 and 38 off. However, once the coil 24 has been changed to the ON position, it remains in that position even after the power has been removed from its terminals 24+ and 24-.

At T2 switch 16 is turned off and the command line 14 starts floating again. The biasing on transistor 44 is set so that when line 14 starts floating, transistor 44 turns on and line 40 goes low (see Figure 3). This turns transistors 32 and 34 on. Transistor 32 applies a positive voltage to the negative terminal (24-) of relay coil 24 while transistor 34 grounds the positive terminal (24+). As a result the coil 24 is changed to its off position. After about 50 ms the transistor 44 turns off and input line 40 goes high, thereby turning off transistors 32 and 34. In this manner the coil 24 is de-energized and is ready to be turned on again at a future time. The transistors 44 and 52 and the RC networks associated therewith form respective sensors for sensing transitions of commands on commercial lines 14, 30 and operate to open or close the coil 24 in response to said transition.

The overload sensor circuit 28 is provided optionally to monitor the power delivered to the device 12. The sensor may include for example a current detector. When this sensor senses an excessive power drain, it is used to activate the electronic controller 20 to turn the relay 22 off. For example, if the configuration shown in Figure 2 is used then, in the presence of a power drain, the overload sensor may short the line 30 to ground. This operation in effect overrules the operation of switch 16 by turning transistor 44 on in the sequence described above. However, once the relay 22 turns off, the ground on line 30 has to be maintained until the condition causing the overload is repaired. Otherwise the relay is re-energized once the sensor 28 fails to detect an overload. Preferably the electronic controller 20 and sensor circuit 28 (if present) are manufactured as a single unitary chip (i.e., an Application Specific IC, or ASIC) which can be mounted in a common housing (not shown) with relay 22. The electronic relay controller described has several important advantages. It can be used with simple on/off control switches, since the controller internally generates the short pulses required to operate the coil(s) of the bistable relay. It is operational over a wide temperature range and needs a low control current. If mounted inside the relay housing, the controller saves the cost of a PCB, it makes the assembly of the system easier and more reliable and provides better heat dissipation. It also reduces the complexity of wiring. A further advantage is that, as seen in Figure 1 , the ASIC is powered from the same bus as switch 16. Therefore, if the line 14 starts floating because power on the bus is lost, the circuit positively switches the load 12 off. In this manner, the circuit insures that turning the ignition key off (which cuts power to the bus) assures that the load is switched off as well.

Numerous modifications may be made to the invention without departing from its scope as defined in the appended claims.

Claims

I claim:

1. A control circuit for operating an electrical device, said control circuit comprising: a. a relay having a relay coil and a contact selectively activated by said relay coil, said contact being adapted to control said electrical device; and b. an electronic controller receiving a command and in response selectively activating said relay, said electronic circuit including a plurality of electronic switches.

2. The circuit of claim 1 wherein said electronic controller includes a plurality of transistors arranged to define a bridge with two input and two output terminals, said relay coil being connected to said output terminals.

3. The circuit of claim 2 wherein said relay is a bistable relay having a first state and a second state and wherein said electronic controller is adapted to set said relay to said first state in response to a first command and to a second state in response to a second command.

4. The control circuit of claim 2 wherein said electronic controller includes a timer for generating a time period for temporarily switching at least some of said transistors to operate said relay coil, said transistors being de- energized after said time period.

5. The control circuit of claim 1 further comprising an overload sensor, said overload sensor activating said electronic controller when an overload of said electrical device is sensed to disconnect said device.

6. The control circuit of claim 2 further comprising a switch selectively coupled to a battery bus to generate said command, said electronic controller being powered by said battery bus, wherein said electronic controller is arranged and constructed to switch said electrical device off when said battery bus loses power.

7. A relay controller for selectively applying power to an electrical device in response to a command, said relay controller comprising: (a) a bistable relay, said relay including a relay coil having a first and a second position and a contact, said relay coil being set to said first position in response to a first signal and to said second position in response to a second signal, said contact being closed in said first position and closed in said second position for selectively providing power to said electrical device; and (b) an electronic controller responsive to said command, said electronic controller including an electronic switch which temporarily operates said relay coil in response said command.

8. The controller of claim 7 wherein said electronic switch includes a set of switching transistors forming an H-bridge, with said relay coil being connected across said bridge.

9. The controller of claim 8 wherein said switching transistors includes a first pair and a second pair of switching transistors.

10. The controller of claim 9 wherein said electronic controller includes a first input transistor for temporarily activating said first pair of switching transistors in response to said command and a second input transistor for temporarily activating said second pair of switching transistors.

11. The controller of claim 10 wherein said input transistors generate input pulses corresponding to transitions of said command.

12. The controller of claim 7 wherein said electronic controller includes a transition sensor for sensing transitions of said command, said electronic switch being activated by said transitions.