GB2037114A - A turn-off accelerating circuit for use with a power transistor - Google Patents
A turn-off accelerating circuit for use with a power transistor Download PDFInfo
- Publication number
- GB2037114A GB2037114A GB7940736A GB7940736A GB2037114A GB 2037114 A GB2037114 A GB 2037114A GB 7940736 A GB7940736 A GB 7940736A GB 7940736 A GB7940736 A GB 7940736A GB 2037114 A GB2037114 A GB 2037114A
- Authority
- GB
- United Kingdom
- Prior art keywords
- turn
- capacitor
- transistor
- diode
- 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- Withdrawn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
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
-
- 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
- H03K17/04213—Modifications for accelerating switching by feedback from the output circuit to the control circuit in bipolar transistor switches
Abstract
A darlington-connected power transistor pair, (T3,T4) switches current flowing through a load (13) and a flywheel circuit (C3, 24, 16). The current is drawn from mains (11) via a rectifying bridge (12) or from a standby battery (10), and the voltage applied to the load (13) is regulated by a circuit (23) which modulates the duty ratio of a rectangular wave applied to the base of the power transistor (T3, T4). Two techniques for assisting transistor turn-off are combined. During turn-off, a quench circuit comprising a first capacitor (1) and a diode (D1) shunts current around the power transistor until it is fully turned off. The first capacitor (C1) discharges during the next on period via the power transistor and a resistor (R1) to prepare the capacitor for the subsequent turn off. Part of the voltage then appearing across the resistor (R1) is used to charge a second capacitor (C2) via a second diode (D4) to provide a source of turn-off bias potential (point A) lying outside the range of potentials provided by the battery or the diode bridge. The quench circuit thus also acts as the primary source for the turn-off bias potential. The availability of such a source reduces the turn-off time of the power transistor and thereby reduces the capacitance required of the quench circuit. <IMAGE>
Description
SPECIFICATION
A turn-off accelerating circuit for use with a
power transistor
The invention relates to a turn-off accelerating
circuit for use with a power transistor.
Unless suitable precautions are taken in
electronic circuits which include power transis
tors for switching losses occur in the transistors, and these losses are high when the
switching frequency is high.
Remedies for these difficulties are knows in particular, the turn-off speed of the collector current of an NPN transistor can be in
creased by using a source of negative base
emitter bias potential to evacuate the charge
stored on the base as quickly as possible.
Further, it is advantageous, in particular when the supply voltage of the transistor is high, to
use a quench circuit to shunt current around the transistor when the transistor is turning off, so as to reduce the value of the power dissipated in the transistor; the transistor can then be kept in the dissipation range guaranteed by the manufacturer.
The solution which has just been given for the problem is applied without difficulty when an auxiliary voltage source is available.
If there is no auxiliary voltage available, e.g.
when the transistor is switching current drawn from a standby battery, it is necessary to provide means to assist the transistor to turnoff (clearly so long as AC mains current is available, an extra winding on a transformer could be used to provide a bias source at any desired potential).
Preferred embodiments of the present invention provide a turn-off accelerating circuit suitable for switching the power transistors of a chopper amplifier even when it is fed from only one storage battery, without requiring any auxiliary voltage source.
The present invention provides a turn-off accelerating circuit for use with a power transistor connected as current switch with its collector-emitter circuit connected in series between a load and a source, and with its base selectively connectable to a source of turn-off bias potential; the turn-off accelerating circuit comprising: -a quench portion connected in parallel with the collector-emitter circuit of the transistor, the quench portion comprising a first capacitor connected in series with a first diode, with the capacitor connected to the collector and the diode connected to the emitter, and a first resistance connected in parallel with the first diode; the capacitor-diode circuit serving to shunt current around the transistor during the turn-off time of the transistor, and the resistance serving to discharge the capacitor through the transistor during a following period of transistor conductivity thereby preparing the capacitor to serve again as a current shunt during a subsequent transistor turn-off; and -a bias potential storing portion compris
ing a second capacitor connected in series with a second diode, with the second capacitor connected to the transistor emitter and the second diode connected to the first resistance in such a manner as to cause the second capacitor to be so charged, while the first capacitor is discharging through the first resistance, as to constitute the said source of turnoff bias potential.
Avantageously, the circuit further includes a
Zener diode connected in parallel with the second capacitor to fix the greatest turn-off bias potential that can be stored thereon, and a current-limiting resistor connected in series with the second diode to limit the current flow through the Zener diode.
An embodiment of the invention is described with reference to the accompanying drawings, in which:
Figure 1 is a circuit diagram for feeding a load at constant voltage from a storage battery, the average current in the load being regulated by power transistors controlled by a switching circuit including a turn-off accelerating circuit in accordance with the invention; and
Figures 2a to 2f are waveform diagrams of the turn-off accelerating circuit.
In Fig. 1, a load 13 is powered from AC mains 11 via a rectifier bridge 1 3 and the power supply is backed up by a standby storage battery 1 0. If mains fails the battery supplies current to the load. A diode 1 4 is disposed in a conventional manner in series with the battery to prevent uncontrolled charging from the AC mains. A smoothing capacitor 1 5 is also provided in parallel with the battery.
The current flowing through the load 1 3 is controlled by on/off switching of a darlingtonconnected pair of NPN power transistors T3 and T4. The power transistors T3 and T4 are switched on via a turn-on NPN transistor T1 having its collector connected to the positive power supply rail via a resistor 18; and the power transistors T3 and T4 are switched off by a turn-off PNP transistor T2 connected directly to a point "A" which serves as a source of turn-off bias potential. The transistor
T2 is itself biassed by means of a resistor 1 9 connected berween its collector and its emitter.It will be observed that, while the turn-on transistor T1 can only inject current into the base of the first transistor T3 of the darlington-connected pair (in order to benefit from the darlington connection), the turn-off transistor T2 is connected both directly to the base of the transistor T3 and indirectly to the base of the transistor T4 via a diode 1 7 in order to evacuate charge directly therefrom during turn-off.
The on/off duty ratio of the power transis tors T3 and T4 is varied as a function of the potential appearing across the load 1 3 in order to regulate the said potential. This is done by sensing the potential by means of a potentiometer bridge 20 connected to an operational amplifier 21 which amplifies and isolates the sensed potential. A PNP transistor 22 connected to the output of the operational amplifier and having a potentiometer bridge connected to its collector serves to transpose the isolated and amplified potential away from its reference to the positive rail of the power supply so that it becomes referred to the negative rail.This signal is then applied to the dury ratio control input of a rectangular wave oscillator circuit 23 whose rectangular wave output is applied directly to the bases of the turn-on and turn-off transistors T3 and T4. the oscillator circuit 23 may be a Texas Instruments' integratedcircuit type N" SG 3524, operating at a nominal frequency of 1 kHz.
During periods when the power transistors T3 and T4 are turned off, the flow of direct current through the load 1 3 is maintained by a fly-wheel circuit comprising an inductance 24 connected in series between the load 1 3 and the common collector of the power transistors T3 and T4, a diode 1 6 connected between the said common collector and the positive supply rail, and a capacitance C3 connected in parallel with the load, i.e. in series between the positive supply rail and that end of the inductance 24 which is not connected to the power transistors T3 and T4.
The turn-off accelerating circuit comprises: -a quench portion including a capacitor C1 connected in series with a diode D1 and serving to shunt the flow of current around the transistor T4 during its turn-off time, and a resistor R1 and a diode D2 connected in series around the diode D1 to discharge the capacitor C1 through the transistor T4 when it next becomes conductive, thereby preparing the capacitor C1 to act again as a quench during the following transistor turn-off time; and -a bias potential storing portion comprising a second capacitor C2 connected between the negative supply rail and the said point A, a diode D4 connected in series with a current limiting resistor R2 and that end of the resistance R1 which is not connected to the emitter of the transistor T4, and a Zener diode DZ connected in parallel with the capacitor C2.
The turn-off accelerating circuit operates as follows:
When the transistors T3 and T4 are saturated, the capacitor C1 discharges via the circuit T4, R1 and D2 and via the circuit T4, C2, D4, R2 and D2.
The capacitor C2 stores part of the energy which was previously stored in the capacitor C1 to apply a negative potential to its end which is not connected to the earth (or negative rail) of the circuit (point A). The negative potential allows the charge stored on the bases of the transistors T3 and T4 to be evacuated more rapidly. This increases the switch off speed of the collector current in the transistors T3 and T4.
The Zener diode DZ limits the negative potential to a value which is non destructive to the base-emitter junction of the transistor
T4 which is reverse biased during the turn off phase, while the resistor R2 limits the flow of current through the Zener diode DZ.
The resistor R1 is used for dissipating part of the energy of the capacitor C1, since only a fraction of the energy is necessary for the capacitor C2. The value of C1 is determined by the amount of charge it needs to be capable of storing during transistor turn-off in order to prevent the power transistor from burning out. This in turn depends on how fast the transistor turns-off. Thus, by using a fraction of the energy stored in the quench circuit to charge a source of turn-off bias potential and thereby accelerate turn-off, less energy needs to be shunted in the quench portion than would be required if it were the only portion of the turn-off accelerating circuit.
Nonetheless, in the general case it must still be expected that there will be energy to dissipate. The important point is to dissipate this energy in a resistor, namely R1, rather than in the power transistor which would be destroyed thereby.
The waveforms of Figs. 2a to 2f show respectively:
-Fig. 2a: the voltage U1 between the base of T1 and earth;
-Fig. 2b: the voltage U2 between the base of T3 and earth;
-Fig. 2c: the voltage U4 between the collector of T4 and earth; -Fig 2d: the current IC1 in the capacitor
C1;
-Fig. 2e: the current IC2 in the capacitor
C2; and
-Fig. 2f: the voltage UC2 at the point A.
It is seen that the circuit allows negative voltage to be provided permanently, despite the fact that there is no auxiliary source. The voltage values are given by way of example and have no limiting character.
The invention is in no way limited to the embodiment described. In particular, if PNP power transistors are used, the polarities will be inverted as necessary. Further, if the Zener diode DZ is not required, its current limiting resistor R2 could aiso be omitted. The application of excessive bias voltage to the turn-off transistor T2 and/or to the power transistor
pair T3, T4 could then be avoided either by connecting the diode D4 to a suitable intermediate point along the resistance R1, or by
inserting a resistor in series with the collector
of the turn-off transistor T2, or simply be operating with a low voltage power rail.
Clearly these possibilities can be combined with each other.
The power transistor need not necessarily be a Darlington-connected pair, and indeed, even in the embodiment described, the diode 1 7 effectively removes the " Darlington" nature of the connection during turning off.
Although not suitable for circuits that switch on and off only occasionally, since the turn-off bias potential will have a tendency to leak away from the capacitor C2, the turn-off accelerating circuit of the invention is certainly capable of being used at much lower on/off frequencies than 1 kHz.
Claims (4)
1. A turn-off accelerating circuit for use with a power transistor connected as a current switch with its collector-emitter circuit connected in series between a load and a source, and with its base selectively connectable to a source of turn-off bias potential; the turn-off accelerating circuit comprising: -a quench portion connected in parallel with the collector-emitter circuit of the transistor, the quench portion comprising a first capacitor connected in series with a first diode, with the capacitor connected to the collector and the diode connected to the emitter, and a first resistance connected in parallel with the first diode; the capacitor-diode circuit serving to shunt current around the transistor during the turn-off time of the transistor, and the resistance serving to discharge the capacitor through the transistor during a following period of transistor conductivity thereby preparing the capacitor to serve again as a current shunt during a subsequent transistor turn-off; and -a bias potential storing portion comprising a second capacitor connected in series with a second diode, with the second capacitor connected to the transistor emitter and the second diode connected to the first resistance in such a manner as to cause the second capacitor to be so charged, while the first capacitor is discharging through the first resistance, as to constitute the said source of turnoff bias potential.
2. A turn-off accelerating circuit according to claim 1 and further including a Zener diode connected in parallel with the second capacitor to fix the greatest turn-off bias potential that can be stored thereon, and a currentlimiting resistor connected in series with the second diode to limit the current flow through the Zener diode.
3. A turn-off accelerating circuit according to claim 1 or 2, wherein the power transistor comprises a Darlington-connected pair of power transistors, the bases of both transistors being selectively connectable to the source of turn-off bias potential.
4. A turn-off accelerating circuit for use with a power transistor, the circuit being substantially as herein described with referenced to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7833475A FR2442552A1 (en) | 1978-11-27 | 1978-11-27 | AID CIRCUIT FOR SWITCHING POWER TRANSISTORS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2037114A true GB2037114A (en) | 1980-07-02 |
Family
ID=9215409
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7940736A Withdrawn GB2037114A (en) | 1978-11-27 | 1979-11-26 | A turn-off accelerating circuit for use with a power transistor |
Country Status (4)
| Country | Link |
|---|---|
| DE (1) | DE2947003A1 (en) |
| ES (1) | ES486368A1 (en) |
| FR (1) | FR2442552A1 (en) |
| GB (1) | GB2037114A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2517498A1 (en) * | 1981-12-02 | 1983-06-03 | Faiveley Sa | Current pulse amplifier - has inversion transformer circuit connecting collector emitter path of control transistor with base of output power transformer |
| EP0085812A1 (en) * | 1981-12-22 | 1983-08-17 | Hughes Aircraft Company | Base drive circuit |
| DE3319090A1 (en) * | 1982-05-26 | 1983-12-01 | Raytheon Co., 02173 Lexington, Mass. | COMPARATIVE CIRCUIT |
| US4602209A (en) * | 1983-06-24 | 1986-07-22 | Williams Barry W | Switch-off circuits for transistors and gate turn-off thyristors |
| CN102324833A (en) * | 2011-06-10 | 2012-01-18 | 无锡友达电子有限公司 | Integrated circuit special for electric vehicle driver designed with low-voltage process |
| CN113363943A (en) * | 2021-05-17 | 2021-09-07 | 深圳易马达科技有限公司 | Overcurrent protection circuit of battery and power supply equipment |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3571614A (en) * | 1968-08-05 | 1971-03-23 | Hughes Aircraft Co | Transistor switch with minimized transition power absorption |
| US3641424A (en) * | 1970-11-20 | 1972-02-08 | Trw Inc | Regenerative voltage regulators |
| DE2718996C2 (en) * | 1977-04-28 | 1979-03-01 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Circuit arrangement for reducing the turn-off losses in semiconductor switches |
-
1978
- 1978-11-27 FR FR7833475A patent/FR2442552A1/en not_active Withdrawn
-
1979
- 1979-11-21 DE DE19792947003 patent/DE2947003A1/en not_active Withdrawn
- 1979-11-26 GB GB7940736A patent/GB2037114A/en not_active Withdrawn
- 1979-11-27 ES ES486368A patent/ES486368A1/en not_active Expired
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2517498A1 (en) * | 1981-12-02 | 1983-06-03 | Faiveley Sa | Current pulse amplifier - has inversion transformer circuit connecting collector emitter path of control transistor with base of output power transformer |
| EP0085812A1 (en) * | 1981-12-22 | 1983-08-17 | Hughes Aircraft Company | Base drive circuit |
| DE3319090A1 (en) * | 1982-05-26 | 1983-12-01 | Raytheon Co., 02173 Lexington, Mass. | COMPARATIVE CIRCUIT |
| GB2121255A (en) * | 1982-05-26 | 1983-12-14 | Raytheon Co | Comparator circuit |
| US4602209A (en) * | 1983-06-24 | 1986-07-22 | Williams Barry W | Switch-off circuits for transistors and gate turn-off thyristors |
| CN102324833A (en) * | 2011-06-10 | 2012-01-18 | 无锡友达电子有限公司 | Integrated circuit special for electric vehicle driver designed with low-voltage process |
| CN102324833B (en) * | 2011-06-10 | 2014-01-08 | 无锡友达电子有限公司 | Integrated circuit special for electric vehicle driver designed with low-voltage process |
| CN113363943A (en) * | 2021-05-17 | 2021-09-07 | 深圳易马达科技有限公司 | Overcurrent protection circuit of battery and power supply equipment |
| CN113363943B (en) * | 2021-05-17 | 2022-06-07 | 深圳易马达科技有限公司 | Overcurrent protection circuit of battery and power supply equipment |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2442552A1 (en) | 1980-06-20 |
| ES486368A1 (en) | 1980-05-16 |
| DE2947003A1 (en) | 1980-06-04 |
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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) |