GB2095942A - Transistor drive circuit - Google Patents
Transistor drive circuit Download PDFInfo
- Publication number
- GB2095942A GB2095942A GB8207186A GB8207186A GB2095942A GB 2095942 A GB2095942 A GB 2095942A GB 8207186 A GB8207186 A GB 8207186A GB 8207186 A GB8207186 A GB 8207186A GB 2095942 A GB2095942 A GB 2095942A
- Authority
- GB
- United Kingdom
- Prior art keywords
- transistor
- base
- transformer
- winding
- circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/04—Modifications for accelerating switching
- H03K17/042—Modifications for accelerating switching by feedback from the output circuit to the control circuit
- H03K17/0424—Modifications for accelerating switching by feedback from the output circuit to the control circuit by the use of a transformer
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/04—Modifications for accelerating switching
- H03K17/041—Modifications for accelerating switching without feedback from the output circuit to the control circuit
- H03K17/0412—Modifications for accelerating switching without feedback from the output circuit to the control circuit by measures taken in the control circuit
- H03K17/04126—Modifications for accelerating switching without feedback from the output circuit to the control circuit by measures taken in the control circuit in bipolar transistor switches
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
- H03K17/60—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors
- H03K17/601—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors using transformer coupling
Abstract
A transistor drive circuit comprises a transistor 10 the collector of which is connected through the primary winding 12 of a transformer 14 to a positive terminal 16 and the emitter of which is connected to a negative terminal 18. The terminals 16 and 18 are connected to points of the circuit in which transistor 10 is utilised.The transformer 14 has a secondary winding 20 which is connected across the base emitter junction of transformer 10 and a control winding 24. The control winding 24 is driven by a current source circuit 30 which in turn is driven by a square wave oscillator having Q and Q outputs. In operation, when the Q output of the oscillator goes high, a high current pulse flows through the control winding 24 thereby supplying a turn-off pulse to the transistor 10. At the end of the high current pulse, the current source circuit 30 supplies a low residual current to the control winding 24. When the Q output of the oscillator 64 goes low, the residual current is terminated with the result that the energy stored in the transformer 14 causes a turn-on pulse to be supplied across the base emitter junction of the transistor 10. When the transistor 10 is in its on state, the transformer 14 operates as a feedback path to provide base current to the transistor 10 from its collector circuit. Alternatively, the control winding may be on a separate transformer (303,Fig 5) whose secondary is connected to the base of the transistor. <IMAGE>
Description
SPECIFICATION
Transistor drive circuit
This invention relates to a drive circuit for a transistor and particularly, but not exclusively, to a drive circuit for a high voltage transistor.
In order to avoid supplying excessive power to the base of a transistor, the base current should vary in accordance with the collector current and ideally the ratio of the collector current to the base current should be equal to the saturated gain of the transistor. In one known arrangement, this is achieved by providing a transformer having a primary winding connected to the collector path of the transistor and a secondary winding connected across the baseemitter path of the transistor. This arrangement avoids the necessity of supplying base current through a current limiting resistor and the power loss associated with such a resistor. With this arrangement, in order to turn the transistor on it is only necessary to apply a short low power positive pulse to the base of the transistor.In order to turn the transistor off the whole of the forward base current must be diverted and additional reverse base current must be provided to achieve the required turn-off speed. Where isolation is not required between the control circuit for the transistor and the transistor ouput circuit, the turn-on and turn-off currents may be supplied directly from the control circuit to the base of the transistor. Where isolation is required the turn-on and turn-off currents may not be directly supplied to the transistor base and it it an object of this invention to provide a new or improved transistor drive circuit which allows for isolation between the transistor control circuit and the transistor output circuit.
According to this invention there is provided a transistor drive circuit comprising a transistor, a transformer having a primary winding connected in series with the collector-emitter path of the transistor and a secondary winding connected across the base-emitter path of the transistor, and a control winding arranged either as a further winding of said transformer or as the primary winding of a second transformer the secondary winding ofwhich is connected across the base-emitter path of the transistor.
In order to turn the transistor on and offappropriate turn-on and turn-off signals are applied to the control winding. As the control winding is isolated from the output circuit of the transistor, the control circuit which produces these signals is also isolated.
In a preferred arrangement, the control winding is driven by a current source circuit, the current source circuit being arranged to provide a high current turn-off pulse and a small residual current following the turn-off pulse and to terminate the residual current to turn-on the transistor.
The high current turn-off pulse provides the necessary reverse drive current for turning-off the transistor and when the residual current is term in ated the enery associated with this current is converted into a forward drive pulse for turning-on the transistor. Because the transistor is turned-on by terminating the residual current there is no need to provide forward and reverse currents to the control winding.
Where the control winding is arranged as the primary winding of a second transformer the secondary winding of which is connected across the base-emitter path of the transistor, a diode may be connected between the secondary winding of the first transformer and the base of the transistor with the same polarity as the base-emitter path of the transistor.
By connecting a diode between the secondary winding and the base of the transistor, a higher reverse voltage on the windings of the firsttransfor- mer is permissible when the transistor is turned-off thereby allowing the transistor to be turned-on for a higher proportion of each duty cycle.
This invention will now be described in more detail, by way of example, with reference to the accompanying drawings in which:
Figure 1 is a circuit diagram of a transistor drive circuit embodying this invention;
Figure 2 shows waveforms appearing in the circuit of Figure 1;
Figure 3 shows a modification of the circuit shown in Figure 1;
Figure 4 shows another modification of the circuit shown in Figure 1;
Figure 5shows a further modification of the circuit shown in Figure 1;
Figure 6 is a circuit diagram of a push-pull DC to
DC converter which includes a pair of transistor drive circuits as shown in Figure 1, and
Figure 7 is a circuit diagram of another transistor drive circuit embodying this invention.
Referring now to Figure 1 there is shown a drive circuit for a transistor 10. The transistor 10 is a high voltage bi-polar NPN transistor and may, for example, be a Mullard type BUX80 transistor. The collector of transistor 10 is connected through the primary winding 12 of a transformer 14to a positive terminal 16 and its emitter is connected to a negative terminal 18. The terminals 16 and 18 in use are connected to appropriate points of a circuit in which the transistor 10 is utilised.
The transistor 14, which forms part of a base circuit 19, is a 1 :n step up transformer and has a secondary winding 20 the ends of which are connected respectively to the base and emitter of transistor 10. The transformer 14 operates as a feedback path to provide base current to transistor 10 from its collector circuit and the transformer 14 is arranged so that its magnetising current is small compared with the collector and base currents. The transfomer ratio n is chosen to be equal to the lowest saturated gain of the transistor 10 within the working range of the collector current and the base current is maintained at 1/n of the collector current irrespective of the collector current or the supply voltage of the drive circuit. In this present example, the transistor 10 is arranged to operate with a 9A collector current and a 3A base current.The secondary winding 20 is bridged by a resistor 22 to damp spurious oscillations in transformer 14 which might otherwise cause the transistor 10 to turn-on accidentally.
The base circuit 19 includes a control winding 24 which forms part of transformer 14 and which is provided as will be explained in more detail below forturning transistor 10 on and off. The ends ofthe winding 24 are connected respectively to a pair of rails 26 and 28 by which it is connected to a current source circuit 30. The control winding 24 and secondary winding 20 are arranged as a 2:1 or 3:1 step-down transformer so as to reduce the current required from the current source 30.
The current source circuit 30 comprises a 1 0V supply rail 32 which is connected to rail 26 and an OV rail 34. The rail 32 is connected through a resistor 36 to the collector of an NPN transistor 38, the base of which is connected to the output of a monostable 40 and to the collector of an NPNtransistor42,the emitter of which is connected to the rail 34. The emitter of transistor 38 is connected through a resistor 44 to the rail 34 and also to the base of an
NPN transistor 46, the emitter of which is connected through a resistor 48 to the rail 34 and directly to the base of transistor 42. The collector of transistor 46 is connected to a rail 52 which is connected to the rail 28 and the collector of transistor 46 is also connected to the cathode of a diode 50, the anode of which is connected to rail 34.When a high signal is applied to the base of transistor 38 the transistors 38, 42 and 46 operate in the present example as a 3A current source for the control winding 24. The diode 50 provides a path for permitting reverse current to flow through the winding 24 when the transistor 10 is turned-off so as to dissipate energy stored in the transformer 14 while the transistor 10 is turned-on.
The rail 32 is connected through a resistor 54 to the collector of an NPN transistor 56 and to the base of an NPN transistor 58. The collector of transistor 58 is connected to rail 52 and the emitter is connected through a resistor 60 to the base of transistor 56 and through a resistor 62 to the rail 34. The emitter of transistor 56 is connected to the rail 34.
The drive circuit shown in Figure 1 includes a square wave oscillator 64, the Output of which is connected to the input of monostable 40 and the output of which is connected through a resistor 66 to the base of transistor 56. When the Q-output of oscillator 64 goes low, transistors 56 and 58 operate in the present example as a 50mA current source for the control winding 24.
The operation of the drive circuit shown in Figure 1 will now be described with reference to Figure 2 in which graph A represents the Q-output of oscillator 64 and graph B represents the currentwaveform in control winding 24. When the Output of oscillator 64 is low, the transistor 10 is in the on state with the base current supplied by thefeed-back operation of transformer 14. When the Q-output of oscillator 64 goes high, monostable 40 is triggered thereby causing a 3A pulse to flow through control winding 24 which causes the secondary winding 20 to apply a reverse bias pulse across the base-emitter junction of tansistor 10 thereby turning if off.When the
Q-output of oscillator 64 goes high, the Q-output goes low and so a residual 50mA current continues to flow through the control winding 24 after the 3A pulse is terminated. When the Output goes low, the 50mA residual current is terminated with the result that the energy associated with this current is converted by the transformer 19 into a pulse which turns on transistor 10.
It is to be noted that the current source circuit 30 and oscillator 64 are isolated by the transformer 14 from the output circuit of transistor 10. Also, because the transistor 10 is turned on by terminating the residual 50mA current in winding 24, there is no need to provide a dual polarity voltage supply for the control winding 24.
Referring now to Figure 3 there is shown a modification of the base circuit 19, and in this circuit like elements are denoted by the same reference numerals preceded by the number "1". In the circuit of Figure 3, the control winding 124 is connected through an inductor 101 to the rail 128, the junction of winding 124 and inductor 101 being connected to the cathode of a zener diode 102. The anode of zener diode 102 is connected to the anode of diode 103, the cathode of which is connected to rail 128. The inductor 101 stores energy during the first part of turn-off of transistor 10 and this energy is released during the second part of turn-off in the form of a high value reverse voltage pulse across the baseemitter junction of transistor 110.This reverse pulse causes break-down ofthisjunction and rapid termination of the second part of turn-off. The zener diode 102 is provided to prevent inductor 101 interfering with the first part of turn-off.
Referring now to Figure 4 there is shown another modification of the base circuit 19 and in this circuit like elements are denoted by the same reference numerals preceded by the number "2". In this circuit the secondary winding 220 is connected to the anode of a diode 201, the cathode of which is connected to the collector of transistor 210. Also, the winding 220 is connected to the base of transistor 210 through a pair of parallel connected diodes 202 and 203 having opposing polarities. The diodes 201 and 202 prevent transistor 210 from being driven into hard saturation as base current is diverted through diode 201 before this occurs. The diode 203 provides a path for the reverse base current during turn-off.As tu rn-off time is increased by hard saturation, the modification shown in Figure 4 should be used where it is desired to avoid this increased tu rn-off time.
Referring now to Figure 5 there is shown another modification of the base circuit 19 and in this circuit like elements are denoted by the same reference numerals preceded bythe number "3".
In the circuit of Figure 5 the secondary winding 320 is connected to the anode of a diode 301, the cathode of which is connected to the base of transistor 310.
The diode 301 permits a much greater reverse voltage to develop on the windings of transformer 314 during the transistor off-time thereby increasing the collapse speed of the magnetic flux which develops during the on-time and so increasing the proportion of possible on-time of each duty cycle. It is envisaged that this circuit permits at least 95% on-time during each duty cycle. When using this modification, the oscillator 64 may also be modified so as to achieve the increased on4ime.
As the diode 301 prevents reverse drive from being applied through the secondary winding 320, in the circuit of Figure 5 the control winding 324 forms the primary winding of a transformer 303. One end of the secondary winding 304 of transformer 303 is connected to the emitter of transistor 310 and the other end is connected to the anode of a diode 305, the cathode of which is connected to the base of transistor 310. The diode 305 is bridged by a pair of diodes 306 and 307 of opposite polarity to diode 305.
The diodes 306 and 307 prevent the base current from flowing through winding 304, and the diode 305 provides a path for the turn-on pulse.
Referring now to Figure 6 there is shown a DC to
DC switched mode push-pull converter. Th converter comprises a pair of positive and negative DC input rails 401 and 402. The rail 401 is connected to the collector of a high voltage bi-polar NPN transistor 510, the emitter of which is connected to the collector of a further high voltage NPN bi-polar transistor 610. The emitter of transistor 610 is connected to the rail 402. The rail 401 is also connected through a pair of capacitors 403 and 404 to the rail 402. The emitter of transistor 510 is connected through the primary winding 405 of a transformer 406 to the junction of capacitors 403 and 404. One end of the secondary winding 407 of the transformer 406 is connected to the anode of a diode 408, the cathode of which is connected through an inductor 410 to a positive DC output rail 411.The other end of winding 407 is connected to the anode of a diode 409, the cathode of which is connected to the cathode of diode 408. A central tapping of winding 407 is connected to a negative DC output rail 412 and the rails 411 and 412 are connected by a smoothing capacitor 413.
The converter also includes a square wave oscilla tor 414which drives transistor 510 through a monostable 415, a current source circuit 530 and a base circuit 519 and which drives transistor 610 out of phase with transistor 510 through a monostable 416, a current source circuit 630 and a base circuit 619. The current source circuits 530 and 630 are identical to the current source circuit 30 shown in
Figure 1 and the base circuits 519 and 619 are identical to the base circuit 19.
In operation, the transistors 510 and 610 are turned on alternately and output current is supplied alternately through diodes 408 and 409.
Referring now to Figure 7 there is shown a drive circuit for a high voltage bi-polar NPN transistor 710.
The collector of transistor 710 is connected to a positive terminal 712 and the emitter is connected through the primary winding 714 of a transformer 716 to a negative terminal 718. The terminals 712 and 718 in use are connected to appropriate points of a circuit in which the transistor 710 is utilised.
The transformer 716 includes a secondary winding 720 the ends of which are connected respectively to the base and emitter of transistor 710. The primary and secondary windings 714 and 720 are arranged as a voltage step-up transformer. The windings 714 and 720 operate as a feedback path to provide base cu rrent to transistor 710 from its emitter circuit.
The tra nsformer 716 is also provided with a pair of control windings 722 and 724. The winding 722 is associated with a turn-on circuit 726 and the winding 724 is associated with a turn-off circuit 728.
The turn-on circuit 726 is provided with an input terminal 730 which is connected to the non-inverting input of a type CA3130 operational amplifier 732.
The inverting input of amplifier 732 is connected to the junction of a pair of resistor 734 and 736 connected in series between an 8V rail and an earth rail. The output of amplifier 732 is connected through a resistor738tothe8V rail and through a resistor 740 to the base of an NPN transistor 742. The collector of transistor 742 is connected through a resistor 744 to the 8V rail and its emitter is connected to the earth rail. The collector of transistor 742 is also connected through a resistor 746 to the base of an
NPN transistor 748, the emitter of which is connected to the earth rail. The collector of this transistor is connected through a pair of zener diodes 750 and 752 to the earth rail and also through a diode 754 to the earth rail.The collector of transistor 748 is also connected through a resistor 756 to one end of winding 722, the other end of which is connected to a 12V rail.
In the turn-off circuit, the collector of transistor 742 is connected through a capacitor 760 and a resistor 761 to the 8V rail and the junction of capacitor 760 and resistor 761 is connected to the base of an NPN transistor 762. The emitter of transistor 762 is connected to the earth rail and its collector is connected through a resistor 764 to the 8V rail and also through a capacitor 766 and a pair of resistors 768 and 770 to the earth rail. The junction of resistors 768 and 770 is connected to the non-inverting input of a type CA3130 operational amplifier 772. The output of amplifier 772 is connected through a resistor 774 to the base of an NPN transistor 775, the collector of which is connected through a resistor 778 to the 1 2V rail and the emitter of which is connected through a resistor 780 to the earth rail.
The emitter of transistor 776 is also connected to the base of an NPN transistor 782, the emitter of which is connected through a resistor 784 to the earth rail and also through a resistor 786 and a capacitor 788, connected in parallel, to the inverting input of amplifier 772. The collector of transistor 782 is connected to the cathode of a diode 790, the anode of which is connected to the earth rail. Lastly, the collector of transistor 782 is connected to one end of control winding 724 the other end of which is connected to the 12V rail.
In operation, a square wave signal is supplied to the input terminal 730. As will be described, the mark space ratio of this signal corresponds to the desired ratio of the off-time to the on-time of transistor 710.
When the square wave signal goes low, the output of amplifier 732 goes low thereby turning-off transistor 742, turning-on transistor 748 and thereby supplying a turn-on pulse across the base emitter junction of transistor 710. When the square wave signal goes high, the output of amplifier 732 goes high thereby turning-on transistor 742. When this happens, tran sistor 762 turns-off for a period determined by resistor 761 and capacitor 760 and a positive pulse is supplied to the non-inverting input of amplifier 772.
When a high signal is supplied to this input of amplifier 772, amplifier 772 together with transistor 776 and 782 operate as a current source. Consequently, a current pulse is supplied to the control winding 724 thereby causing a reverse current pulse to be applied to the base emitter junction of transistor 710 thereby turning the transistor off.
Claims (8)
1. A transistor drive circuit comprising a transistor, a transformer having a primary winding connected in series with the collector-emitter path of the transistor and a secondary winding connected across the base-emitter path of the transistor, a control winding arranged as a further winding of said transformer or as the primary winding of a second transformer the secondary winding of which is connected across the base-emitter path of the transistor.
2. Atransistor drive circuit as claimed in Claim 1 in which the control winding is driven by a current source circuit, the current source circuit being arranged to provide a high current turn-off pulse and a small residual current following the turn-off pulse and to terminate the residual current to turn-on the transistor.
3. A transistor drive circuit is claimed in Claim 1 or Claim 2 including an inductor connected in series with the control winding.
4. A transistor drive circuit as claimed in Claim 1 or Claim 2 in which one end of the secondary winding is connected to the base of the transistor through a first diode having the same polarity as the base-emitter path of the transistor, said one end is connected to the base of the transistor through a second diode having the reverse polarity to the first diode, and said one end is connected to the collector of the transistor through a third diode having the same polarity as the first diode.
5. A transistor drive circuit as claimed in Claim 1 or Claim 2 in which the control winding is arranged as the primary winding of a second transformer the secondary winding of which is connected across the base-emitter path of the transistor and in which at least one diode is connected between the secondary winding of the first transformer and the base of the transistor with the same polarity as the base-emitter path of the transistor.
6. A transistor drive circuit as claimed in Claim 1 in which there are a pair of control windings, the first control winding being driven by a circuit for providing a turn-on pulse and the second control winding being driven by a circuit for providing a turn-off pulse.
7. A transistor drive circuit substantially as hereinbefore described with reference to and as shown in Figure 1, or Figures 1 and 3, or Figures 1 and 4, or Figures 1 and 5, or Figure 7 of the accompanying drawings.
8. A switched mode DC to DC converter substantially as hereinbefore described with reference to and as shown in Figures 1 and 6 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8207186A GB2095942A (en) | 1981-04-01 | 1982-03-11 | Transistor drive circuit |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8110175 | 1981-04-01 | ||
| GB8207186A GB2095942A (en) | 1981-04-01 | 1982-03-11 | Transistor drive circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2095942A true GB2095942A (en) | 1982-10-06 |
Family
ID=26278973
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8207186A Withdrawn GB2095942A (en) | 1981-04-01 | 1982-03-11 | Transistor drive circuit |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2095942A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2124050A (en) * | 1982-06-28 | 1984-02-08 | Gould Instr | Semiconductor switching circuits |
| GB2493562A (en) * | 2011-08-12 | 2013-02-13 | E2V Tech Uk Ltd | Acceleration or deceleration of MOSFET switching using inductive feedback |
-
1982
- 1982-03-11 GB GB8207186A patent/GB2095942A/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2124050A (en) * | 1982-06-28 | 1984-02-08 | Gould Instr | Semiconductor switching circuits |
| GB2493562A (en) * | 2011-08-12 | 2013-02-13 | E2V Tech Uk Ltd | Acceleration or deceleration of MOSFET switching using inductive feedback |
| GB2493562B (en) * | 2011-08-12 | 2018-10-17 | E2V Tech Uk Limited | Drive circuit and method for a gated semiconductor switching device |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |