Title:
DRIVE CIRCUIT FOR CONDUCTING DEVICES
United States Patent 3795826
Abstract:
A drive circuit for effecting current flow in an inductive circuit comprising a coil the circuit including a power transistor having its emitter collector circuit connected in series with the coil, an input transistor for controlling the power transistor and a resistor for providing a signal representative of the current flowing in the coil. A feed back transistor is supplied with the signal developed across the resistor and provides feed back to the input transistor whereby the mean value of current flowing in the coil will depend upon the magnitude of the input signal applied to the input transistor.


Inventors:
ADEY A
Application Number:
05/271199
Publication Date:
03/05/1974
Filing Date:
07/12/1972
Assignee:
C.A.V. Limited (Birmingham, EN)
Primary Class:
Other Classes:
123/357, 315/209R
International Classes:
F02D41/40; H01F7/06; H01H47/32; H02K33/00; (IPC1-7): H03K5/00
Field of Search:
307/268,269,270 123
View Patent Images:
Other References:

IBM Technical Disclosure Bulletin; Vol. 11, No. 11, April 1969; by Johnson, page 1,403..
Primary Examiner:
James, Andrew J.
Attorney, Agent or Firm:
Holman & Stern
Claims:
1. A drive circuit for effecting current flow in an inductive circuit and comprising in combination, a power transistor having its emitter collector circuit connected in series with the inductive circuit, an input transistor for supplying base drive to the power transistor, an input terminal to the drive circuit, the base of said input transistor being connected to said input terminal so as to receive an input signal therefrom, a resistor connected in the emitter collector circuit of said power transistor and across which is developed a signal representative of the current flowing in the inductive circuit, and negative feedback means controlled by the signal developed across said resistor for opposing change in the input signal applied to the base of the input transistor whereby the mean value of current flowing in the inductive circuit will

2. A drive circuit as claimed in claim 1 in which the negative feedback means controlled by said signal comprises a feedback transistor arranged to provide a current supply to the base of the input transistor which

3. A drive circuit as claimed in claim 2 in which the emitter of the

4. A drive circuit as claimed in claim 3 in which a positive feedback path is provided between the power transistor and the input transistor whereby the power transistor and the input transistor operate in the switching

5. A drive circuit as claimed in claim 4 in which said positive feedback

6. A drive circuit as claimed in claim 5 including means for controlling

7. A drive circuit as claimed in claim 6 in which said means for controlling the rate of change of current comprises a capacitor connected

8. A drive circuit as claimed in claim 5 including a diode through which the base of said feedback transistor is supplied with the signal

9. A drive circuit as claimed in claim 1 in which the inductive circuit comprises an actuator coil which forms part of an actuator for a control member of an internal combustion engine, said input transistor being supplied with a signal indicative of the force required to be exerted on the control member.

Description:
This invention relates to drive circuits for effecting current flow in an inductive circuit and more particularly to a drive circuit for a fuel control rod actuator of a liquid fuel injection pump, the actuator including an actuator coil.

The object of the invention is to provide such a circuit in a simple and convenient form.

A drive circuit of the kind specified comprises in combination, a power transistor having its emitter collector circuit connected in series with the inductive circuit, an input transistor for controlling the power transistor, means for providing a signal representative of the current flowing in the inductive circuit, and means controlled by said signal whereby the mean value of current flowing in the inductive circuit will depend upon the magnitude of an input signal applied to the input transistor.

One example of a drive circuit will now be described with reference to the accompanying circuit diagram.

With reference to the diagram there are provided terminals 10, 11 for connection to the position and negative terminals of a source of d.c. supply. In addition there is provided an input terminal 12 which is connected to the base terminal of a p-n-p transistor T1. The emitter terminal of transistor T1 is connected to terminal 10 by way of resistor R1 and terminal 11 by way of resistor R4, resistors R1 and R4 constituting a potential divider which if desired may be replaced by a source of supplying having a voltage intermediate that of terminals 10 and 11. Moreover, the collector terminal of transistor T1 is connected to terminal 11 by way of resistors R2 and R3 in series.

In addition there is provided an n-p-n transistor T2 which is interconnected in a Darlington pair, with an n-p-n power transistor T3. The base terminal of transistor T2 is connected to a point intermediate the resistors R2 and R3 and the collector terminals of the transistors T2 and T3 are connected to one end of the coil L of an actuator. The other end of the coil is connected to terminal 10 by way of resistor R5. The emitter terminal of transistor T3 is connected to terminal 11. Moreover, the collector terminals of transistors T2, T3 are connected to terminal 10 by way of a resistor R6 which is connected in series with a diode D1 having its cathode connected to terminal 10.

Also provided is a feedback transistor T4 of p-n-p type the base terminal of which is connected to a point intermediate the coil L and the resistor R5 and the emitter terminal of which is connected to terminal 10 by way of resistor R7. The collector terminal of transistor T4 is connected to the base terminal of transistor T1 and also to the collector terminals of transistors T2 and T3 by way of the series combination comprising resistor R8 and capacitor C1.

In operation an increasing negative going input signal applied to terminal 12 will cause an increase in the collector emitter current of transistor T1 and this in turn will increase the current flowing in the collector emitter paths of transistors T2 and T3. An increasing current will therefore flow in the coil L and the voltage drop across resistor R5 will increase.

As a result of the increasing voltage drop across resistor R5 the current flowing in the collector emitter path of transistor T4 will increase and this increase in current will tend to turn off transistor T1. An equilibrium condition will be established at which the current flowing in the collector emitter path of transistor T4 will approximately balance, the input signal, and therefore the mean value of the current flowing in the coil L will depend upon the magnitude of the input signal. As the input signal increases in magnitude so also will the mean value of the current flowing in the coil.

Resistor R8 and the capacitor C1 are provided so that positive feedback is applied to transistor T1. The application of positive feedback results in transistors T2 and T3 operating in the switching mode thereby reducing the heat dissipation therein.

A further capacitor C2 may be connected intermediate the base and collector terminals of transistor T1. This will have the effect of controlling the rate of change of current in transistor T3 thereby reducing the interference caused to other electrical circuits.

Furthermore, a further diode D2 may be connected in series with the base terminal of transistor T4 and the point intermediate resistor R5 and the coil L and a further resistor R9 is connected between the base terminal of transistor T4 and terminal 11. The effect of the resistor R9 and diode D2 is to make the relationship between the value of the input signal and the current flowing in the coil more linear and also less sensitive to temperature variations.

In FIG. 2 there is shown a diesel engine 13 upon which is mounted a fuel pump 14 for supplying fuel to the engine. The fuel quantity control rod of the pump is connected to an electromagnetic actuator 15 which incorporates the coil L of the circuit of FIG. 1. The circuit of FIG. 1 is shown as a block 16 and the input signal for the circuit is obtained from a signal processing circuit 17 to which a demand signal is supplied by means of an operator control member 18. The signal supplied to the circuit of FIG. 1 represents an actuator force demand signal and there will also be supplied to the processing circuit 17 signals representing the speed of the engine and also other signals, circuit 17 processing these signals to produce the demand signal.

These other signals will usually include a signal representing the quantity of fuel being supplied to the engine.