GB2093643A

GB2093643A - DC-to-DC converter

Info

Publication number: GB2093643A
Application number: GB8104893A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1981-02-17
Filing date: 1981-02-17
Publication date: 1982-09-02
Also published as: BE892162A

Abstract

In a DC-to-DC converter, two control transistors (T1, T2) are pulse-controlled (Q1, Q2) so as to conduct alternately. Each such transistor has its collector connected to a DC supply via a resistor (R1, R2). Each control transistor, when it conducts derives a pulse through a primary on a control transformer (TF1), the pulses from the two transistors (T1, T2) being oppositely poled. There are two switching transistors (T3, T4) in series across the DC supply to be converted, and they conduct alternately to drive pulses in the opposite sense through a primary winding on an output transformer (TF2). The connection to this output winding is via a further transformer winding via which regenerative feedback for the switching transistor is derived. Thus the primary of output transformer (TF2) receives an alternating pulsed waveform, which is induced into the output transformer's secondary winding. This is rectified by a full- wave rectifier D1-D2 with a choke input filter L--C3 to give a DC output. The arrangement can also function as an inverter if the rectifier circuitry is not included. <IMAGE>

Description

SPECIFICATION DC-to-DC Converter This invention relates to inverters, i.e. DC to AC converters, and to DC-to-DC converters, and especially to such converters for use in mains "off line" systems.

In such systems the DC input to the converter is derived from the mains via a rectifier unit, but it will be understood that the converter proper can be battery driven or driven by a DC generator. An example of an inverter which to some extent resembles the circuit to be described herein is to be found in our British Patent Specification No. 1 527 203 (G.C Bennett - S.G. Radley 8-1). An object of the present invention is to produce a circuit based on principles similar to those of the circuit described in the above-quoted Patent Specification, but which is of a simpler nature.

According to the invention there is provided an inverter, which includes a control transformer whose primary winding is connected to first and second control transistors each of which is resistively coupled to a DC supply line, connections to said transistors via which they are pulse-driven so as to conduct alternately, a first secondary winding on the control transformer which drives a first switching transistor so that the first switching transistor conducts when said first control transistor conducts, a second secondary winding on the control transformer which drives a second switching transistor so that the second switching tansistor conducts when said second control transistor conducts connections from the two switching tansistors a primary winding on an output transformer such that when said first switching transistor conducts the output transformer prirnary winding receives a positive-going pulse and that when said second switching transistor conducts the output transformer primary winding receives negative-going pulses, an output alternating current being derived from a secondary winding on the output transformer, and a further winding on the control transformer to which the pulsed outputs of the switching transistors are also applied, such that the pulsed output of the first switching transistor provides regenerative feedback for the first control transistor and that the pulsed output of the second switching transistor provides regenerative feedback for the second control transistor.

According to the invention there is also provided a DC-to-DC converter, which includes a control transformer whose primary winding is connected to first and second control transistors each of which is resistively coupled to a DC supply line, connections to said transistors via which they are pulsedriven so as to conduct alternately, a first secondary winding on the control transformer which drives a second switching transistor so that the second switching transistor conducts when the second control transistor conducts, connections from the two switching transistors to a primary winding on an output transformer such that when said first switching transistor conducts the output transformer primary winding receives positive-going pulses and that when said second switching transistor conducts the output transformer primary winding receives negative-going pulses, a rectifier circuit connected to an output winding on the output transformer, which rectifier circuit rectifies the alternating current pulsed waveform reaching the secondary winding of the output transformer to provide the converter's DC output, and a further winding on the control transformer to which the pulsed outputs of the first switching transistors are applied, such that the pulsed output of the first switching transistor provides regenerative feedback for the first control transistor and that the pulsed output of the second switching transistor provides regenerative feedback for the second control transistor.

An embodiment of the invention will now be described with reference to the accompanying drawing, in which Fig. 1 is a circuit diagram of a DC to DC converter embodying the invention, and Fig. 2 shows waveforms relevant to the circuit of Fig. 1.

As mentioned above, the present circuit was designed for use in a mains "off-line" system , so that the input DC supply is derived from the AC mains by rectification.

This given the DC supply + V5 to be converted into the DC output V,, and also a DC supply V555 for powereing the control circuitry of the convertor. The DC thus obtained from the mains also poweres pulse generators to produce the pulse waveforms Q1, Q2, Fig.2.

These rectifications and pulse circuits can follow established practice, and thus are not shown.

One example in which the converter of the present invention may be used is an automatic telephone exchange in which the conventional 48 volt supply is derived from the mains, and is also used to drive DC to DC converters for powering transistor circuitry.

In Fig. 1, the control circuitry includes two transistors T1 and T2 each having its collector connected by a resistor Ri and R2 respectively to the DC supply Vaux. The two collectors are also connected to the opposite ends of the primary winding of a control transformer TF1.

The transistors are base driven by the pulse trains Q1, Q2, Fig. 2, so that the transistors conduct alternately with a short dead time between T1's conduction and T2's conduction.

The transformer TF1 has three secondary windings, the polarities of the turns of which are indicated by black dots in the usual manner. Two o these secondaries drive two switching transistors T3 and T4 which are connected in series across the DC supply are two capacitors C1 and C2. The junction between the emitter of T3 and the collector of T4 is connected via a winding of TF1 to the primary winding of an output tranformer TF2.

This feeds the output rectifier circuit D1 - D2, which is a full-wave rectifier, with its choke input filter L1-C3.

In use the control transistors T1 and T2 are rendered conductive alternately by the pulsed waveforms Q1 and Q2. Thus each pulse of conduction by T1 or T2 drives a pulse of current through the primary winding of TF1 in one or the other direction. The pulse in one direction causes switching transistor T3 to conduct and drive a pulse through the middle winding of TF1 and the primary winding of TF2 in series. The pulse in the middle winding of TF1 provides a regenerative feedback for the conducting control transistor which is thus driven hard on. The pulse in the other direction causes T4 to conduct, with regenerative feedback in a similar manner to the other control transistor.

Thus a waveform of the type shown at V1, Fig. 2 is developed across the primary winding of TF2, and is therefore induced into the secondary winding thereof. This waveform is recified by D1 - D2 to produce the DC output.

Choice of voltage V0 is effected by suitably proportioning the transformers so that the voltage is reduced (or increased) as needed from Vs.

The resistors R1 and R2 provide turn-on energy to the transistors T1, T2, and therefrom ultimately to the switching transistors T3, T4. Any irregularities in volt/second products in the supplies to these transistors are automatically balanced out as the transistor's operating point on its B-H loop is free to move. A residual current/flux is developed which opposes the volt/second inequality to provide the balancing action.

It will be appreciated that if the circuit shown is used without the output rectifier circuit, we have an inverter, i.e. a DC-AC converter. Such a circuit is often needed when an alternating current has to be derived from a direct current supply.

Claims

1. An inverter, which includes a control transformer whose primary winding is connected to first and second control transistors each of which is resistively coupled to a DC supply line, connections to said transistors via which they are pulse-driven so as to conduct alternately, a first secondary winding on the control transformer which drives a first switching transistor so that the first switching transistor conducts when said first control transistor conducts, a second secondary winding on the control transformer which drives a second switching transistor so that the second switching transistor conducts when said second control transistor conducts connections from the two switching transistors a primary winding on an output transformer such that when said first switching transistor conducts the output transformer primary winding receives a positive-going pulse and that when said second switching transistor conducts the output transformer primary winding receives negative-going pulses, an output alternating current being derived from a secondary winding on the output transformer, and a further winding on the control transformer to which the pulsed outputs of the switching transistors are also applied, such that the pulsed output of the first switching transistor provides regenerative feedback for the first control transistor and that the pulsed output of the second switching transistor provides regenerative feedback for the second control transistor.

2. A DC-to-DC converter, which includes a control transformer whose primary winding is connected to first and second control transistors each of which is resistively coupled to a DC supply line, connections to said transistors via which they are pulse-driven so as to conduct alternately, a first secondary winding on the control transformer which drives a second switching transistor so that the second switching transistor conducts when the second control transistor conducts, connections from the two switching transistors to a primary winding on an output transformer such that when said first switching transistor conducts the output transformer primary winding receives positive-going pulses and that when said second switching transistor conducts the output transformer primary winding receives negative-going pulses, a rectifier circuit connected to an output winding on the output transformer, which rectifier circuit rectifies the alternating current pulsed waveform reaching the secondary winding of the output transfdrmer to provide the converter's DC output, and a further winding on the control transformer to which the pulsed outputs of the first switching transistors are applied, such that the pulsed output of the first switching transistor provides regenerative feedback for the first control transistor and that the pulsed output of the second switching transistor provides regenerative feedback for the second control transistor.

3. A DC-to-DC converter as claimed in claim 2, wherein the emitter-collector paths of the two switching transistors are connected in series across a DC supply, and wherein the junction between the two switching transistors is connected via the further winding on the control transistor to one end of the primary winding of the output transformer.

4. A DC-to-DC converter as claimed in claim 3, and which includes two capacitors connected in series across the same DC supply as that to which the switching transistors are connected, the junction between the capacitors being corinected to the other end of the primary winding of the output transformer.

5. A DC-to-DC converter, substantially as described with reference to the accompanying drawing.