GB2356755A

GB2356755A - A processor-clocked charge pump for a 42 volt high-side MOSFET switch

Info

Publication number: GB2356755A
Application number: GB0024552A
Authority: GB
Inventors: Bernd Dittmer; Reinhard Rieger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-10-09
Filing date: 2000-10-06
Publication date: 2001-05-30
Anticipated expiration: 2020-10-06
Also published as: FR2799590B1; FR2799590A1; DE19950022A1; GB2356755B; GB0024552D0; JP2001156606A

Description

2356755 CONTROL DEVICE FOR ELECTRONIC SWITCHING MEANS The present

invention relates to a control device for electronic switching means for a load.

An electronic switch for temporary connecting of two terminals is described in DE-A-195 48 612. This switch comprises at least two electrically controllable switching elements, which are arranged in a line between the two terminals. At least one of the electrically controllable switching elements is a field effect transistor or other bidirectional component with an external or integrated overload switching-off facility.

Further, it is known to use relays or so-called smart-power blocks (PROFIET's) for the electronic switching-on of loads in a 12 volt on-board mains of a vehicle. These blocks have only a limited usable range for voltage and current. For higher operating voltages, electronic switching is possible only by power semiconductors, which are provided with a gate driver stage to charge up the gate.

The gate driver stage can be a high-side switch, which are provided for switching of loads lying at one pole at ground, for example at vehicle bodywork. Such a switch, which is preferably an N-channel power MOSFET, lies between the operating voltage and the load and needs a gate voltage above the supply voltage of, for example, + 12 v for switching on. This gate voltage can be produced with use of a charge pump and an oscillator.

In addition, charge pumps according to the Greinacher principle are known for the 12 volt range. These function on the basis of a voltage doubling or voltage tripling.

According to the present invention there is provided a drive control device for a switch for the electronic switching of a load, wherein the switch comprises one or more field effect transistors arranged in series between an operating voltage source and the load, wherein a semi-bridge circuit and a charge pump are provided for generation of the gate voltage of the field effect transistors and wherein an input terminal of the semi-bridge circuit is connected with an output terminal of a processor, at which a clock signal can be generated, with the use of which a gate voltage switching the or one of the field effect transistors to be conductive is generated by means of the circuit and the pump.

2 The clock signal can be a rectangular signal with a frequency in the order of magnitude of 100 kHz and can serve for push-pull drive control of two field effect transistors of the semibridge circuit, wherein one of these field effect transistors is a high-side switch and the other field effect transistor is a low-side switch.

Preferably, the pump comprises a first supply voltage terminal, by way of which a first supply voltage can be fed thereto. The first supply voltage can be 12 volts.

For preference, the first voltage supply terminal is connected by way of a first diode with a first terminal of a charging capacitor, the second terminal of which is connected with the output terminal of the circuit. The first terminal of the charging capacitor can be connected by way of a second diode with a first terminal of a storage capacitor, the second terminal of which ran be connected with the source terminal of the field effect transistor arranged between the load and the operating voltage source. In addition, a first zener diode and a first resistor can be connected in parallel with the storage capacitor, and the first terminal of the storage capacitor can be connected with the gate terminal of the field effect transistor by way of a second resistor. Expediently, the gate terminal of the field effect transistor is connected with the source terminal of the field effect transistor by way of a second zener diode and a resistor which is connected in parallel thereto.

For preference, an emergency switch-off device is provided between the gate terminal of the field effect transistor and the source terminal thereof. This switch-off device can comprise an input terminal for an emergency switch-off signal and a switching transistor, which is brought into the conductive state in the presence of the emergency switch-off signal in order to reduce the difference in potential between the gate terminal and the source terminal of the field effect transistor. The emergency switch-off signal can be derived from an output of the processor.

Preferably, the drain terminal of the field effect transistor is connected with a second supply voltage terminal, by way of which the field effect transistor is connected to a second supply voltage. The second supply voltage can be 42 volts.

By means of a control device embodying the invention the generation of the gate voltage necessary for a connecting through or a making conductive of the switch takes place always in dependence on the presence of a clock signal which is made available at an 3 output of a processor. If the clock signal is present, then the necessary gate voltage is built up and maintained by means of the semi-bridge circuit and charge pump. On switching-off of the clock signal, the gate of the field effect transistor is rapidly discharged, so that the switch blocks. The control of the switch accordingly takes place solely in dependence on a clock signal prepared by the processor and an own oscillator for generation of the clock signal is not necessary. Moreover, a terminal for a switching-off signal feedable to the drive control device is redundant. An additional terminal of that kind can, however, be provided to increase the certainty of switching-off.

The voltage range of the control device is triggered by the input voltage. Merely the pump supply voltage present, which is preferably 12 volts, is raised to the voltage level of the operating voltage, which is preferably 42 volts, in order to make available the positive potential necessary for changing the switch into the conductive state.

Such a control device may have, by comparison with known devices, a reduced component cost. In addition due to the permissible voltage range of the transistors used, the voltage range of the device is increased relative to previous charge pumps. A further advantage is that the magnitude of the pump supply voltage, which is preferably 12 volts, directly sets the value of the control voltage for the switch, for example 42 v + 12 v = 54 v as output voltage.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a schematic circuit diagram of a drive control device embodying the invention.

Referring now to the drawings there is shown a circuit in which a load V is to be acted on with a supply voltage of 42 volts by way of an input switch from an on-board mains of a motor vehicle, this supply voltage being applied to a connecting terminal K2.

The input switch comprises one or more field effect transistors T3, the drain-source paths of which are arranged between the connecting terminal K2 and the load V. In the case of the illustrated embodiment, one field effect transistor of that kind is provided. The drain terminal D of this transistor is connected with the terminal K2 and the source terminal S is connected with the load V.

4 A sufficiently large voltage is required at the gate terminal G of the field effect transistor T3 for connecting it through or making it conductive and for maintaining the connectedthrough operation. This is produced with use of a drive control device, which comprises a half-bridge circuit HB and a charging pump L.

The drive control of the circuit HB is effected by a clock signal CK provided by a processor P at an output Al thereof. This processor can be, for example, a microcontroller of a direct voltage transformer. The clock signal CK at the output Al of the processor P is preferably a rectangular signal with a frequency in the order of magnitude of 100 kHz.

A further terminal A2 of the processor P lies at ground. An emergency switch-off signal NA is available in case of need at an output A3 of the processor P.

The clock signal CK is fed from the output Al of the processor to an input terminal El of the circuit HB, from where it passes by way of a voltage divider to the gate terminal of a switching transistor T6, which conducts and blocks in phase with the clock signal.

A supply voltage terminal (W), at which a supply voltage of 5 volts is present, is connected by way of a resistor with the gate of a field effect transistor TZ the gate of which is connected by way of a diode and two resistors with the gate of a field effect transistor Ti. A zener diode is connected between ground and the gate of the field effect transistor T2. The gate of the field effect transistor TI is connected by way of a resistor and a zener diode, which is parallel thereto, with a connecting terminal K3.

The drain terminals of the field effect transistors T1 and T2 are each connected by way of a respective resistor with a circuit point P1, which forms the output of the circuit HB. The source terminal of the field effect transistor T1, which is the high-side switch of the circuit HB, is connected with the connecting terminal K3. The source terminal of the field effect transistor TZ which forms the low-side switch of the circuit HB, lies at earth potential.

The field effect transistors T1 and T2 are controlled in drive in the sense of a push-pull drive control when the clock signal CK is present, so that the two transistors alternately conduct and block. An intermittent potential is produced at the circuit point or output P1 by this alternation.

When the transistor T2 is conductive, the circuit point Pl is connected with ground by way of the resistor coupled to the drain terminal of T2. The charging capacitor Cl of the pump L can thereby be charged up by way of the diode Dl to the supply voltage of 12 volts made available at a connecting terminal K1.

When the transistor Tl is conductive, the circuit point Pl is acted on, by way of the resistor provided at the drain terminal of the transistor Tl, by the voltage present at the terminal K3. This has the consequence that the diode Dl blocks and the charging capacitor Cl transfers its charge by way of the then-conductive diode D2 to the storage capacitor C2.

When next the transistor T2 is connected through, the circuit point PI is again applied to ground by way of the drain resistor of the transistor T2. The charging capacitor Cl is thereby again charged up by way of Dl to the supply voltage of 12 volts present at the terminal Kl, wherein the diode D2 blocks.

If the transistor T2 is thereafter brought into the blocked state and the transistor Tl into the conductive state, a transfer of the charge stored in the charging capacitor Cl to the storage capacitor C2 takes place again.

The storage capacitor C2 is connected by way of a resistor R2 with the gate G of the field effect transistor T3. The consequence is that the voltage or potential at the gate G of the transistor T3 is raised to such an extent by the afore-described pumping up process that T3 is brought into the conductive state and held therein.

In the conductive state of the transistor T3 the supply voltage of preferably 42 volts at the terminal K2 passes from the on-board mains of the motor vehicle to the load V, which is connected to the source terminal S of the field effect transistor T3. As the source terminal of the transistor T3 is connected with the terminal K3 a total voltage of 12 v + 42 v = 54 v relative to ground builds up in the illustrated circuit at the gate G of the transistor T3, whereas the supply voltage of 42 volts is present between the source terminal S of the transistor and ground. It is ensured by this potential difference between gate and source of the field effect transistor T3 that in operation the transistor is constantly in the conductive state as long as the processor P provides the clock signal CK at its output terminal Al.

6 If the processor P terminates the feed of the clock signal CK to the circuit HB, a rapid decay of the charge of the storage capacitor C2 or of the gate G of the transistor T3 then takes place in the pump L due to the shunt resistors R1 and R3. This has the consequence that the field effect transistor T3 is brought into the blocked state and remains in the blocked state solely by reason of the absent clock signal CK

The certainty of blocking of the transistor T3 can be increased by an emergency switch-off device N. This switch-off device N comprises an input terminal, to which there is applied the switch-off signal NA prepared by the processor- The signal NA passes by way of a voltage divider to the gate of a field effect transistor T4, the source of which lies at ground and the drain of which is connected by way of a resistor with the gate of a further field effect transistor T5. This further field effect transistor T5 switches into the conductive state when the switch-off signal NA is present, whereby a potential equalisation between the gate and the source of the field effect transistor T3 is effected by way of the conductive transistor T5 and a resistor. This has the consequence that the gate of the transistor T3 no longer has the potential which is necessary for the connecting-th rough of the transistor T3 and which is higher relative to the source terminal of the transistor T3.

A parallel circuit of a further zener diode and a resistor is connected between the gate terminal of the transistor T3 and the gate terminal of the transistor T5.

7

Claims

1 A control device for electronic switching means in the form of a field effect transistor connected in series between a load and an operating voltage source for supplying operating voltage for the load, the device comprising a semi-bridge circuit and a charge pump for generating the gate voltage for the transistor, the circuit being connectible at an input thereof to processing means to receive a clock signal therefrom and being responsive to the clock signal to produce the gate voltage for the transistor.

2. A device as claimed in claim 1, wherein the clock signal is a rectangular wave signal with a frequency of substantially 100 kilohertz.

3. A device as claimed in claim 1 or claim 2, wherein the circuit comprises two field effect transistors respectively coupled as a high-side switch and a low-side switch and operable in push-pull mode.

4. A device as claimed in any one of the preceding claims, wherein the pump is connectible to a respective voltage source.

5. A device as claimed in claim 4, wherein the voltage of the voltage source of the pump is 12 volts.

6. A device as claimed in claim 4 or claim 5, wherein the pump comprises a charging capacitor connected at a first terminal thereof with the pump voltage source by way of a diode and at a second terminal thereof to an output of the circuit.

7. A device as claimed in claim 6, wherein the pump compdses a storage capacitor connected at a first terminal thereof with the first terminal of the charging capacitor by way of a further diode and at a second terminal thereof with the source terminal of the transistor between the load and operating voltage source.

8. A device as claimed in claim 7, comprising a zener diode and a resistor connected in parallel with the storage capacitor.

8

9. A device as claimed in claim 8, wherein the storage capacitor is connected with the gate terminal of the transistor between the load and the operating voltage source by way of a further resistor.

10. A device as claimed in any one of the preceding claims, wherein the gate terminal of the transistor between the load and operating voltage source is connected with the source terminal thereof by way of a respective zener diode and a respective resistor connected in parallel therewith.

11. A device as claimed in any one of the preceding claims, comprising additional switching-off means connected between the gate and drain terminals of the transistor between the load and operating voltage source.

12. A device as claimed in claim 11, wherein the additional switching-off means comprises a switching transistor responsive to a switch-off signal to adopt the conductive state and reduce the difference in potential between the gate and drain terminals of the transistor between the load and operating voltage source.

13. A device as claimed in claim 13, wherein the switching means is connectible to receive the switching-off signal from the processing means.

14. A device as claimed in any one of the preceding claims, wherein the field effect transistor between the load and operating voltage source is connectible by way of the drain terminal thereof with that source.

15. A device as claimed in any one of the preceding claims, wherein the operating voltage is 42 volts.

16. A control device substantially as hereinbefore described with reference to the accompanying drawing.