US3025451A - Transistor voltage regulator - Google Patents

Description

March 13, 1962 A. HAKIMOGLU Filed Aug. 13. 1957 g sh t s x SERIES CONSTANT REGULATOR AC VOLTAGE REcr/E/ER FILTER SOURCE TRANSFORMER 15 ERR0R AMPL/F/ER DETECTOR IE IG- 1 INVENTOR.

AYHAN HAKIMOGLU ALA m ATTORNEY 2 Sheets-Sheet 2 Filed Aug. 13. 1957 N OHRAI Unite tates This invention relates generally to regulators, and it has reference in particular to transistor voltage regulators.

While voltage regulators using transistors in series with a load and a supply circuit have been known in the art heretofore, they have usually suffered from a weakness that the transistor would be subjected to excessive heating on overloads and was thus prone to be damaged thereby.

Generally stated, it is an object of the invention to provide a transistor voltage regulator of the series type which is not prone to damage from over-loads.

More specifically, it is an object or" this invention to provide the series transistor regulator wherein the collector-to-ernitter voltage is reduced to substantially Zero upon the occurrence of a predetermined overload.

Another object of this invention is to provide in a transistor regulator for applying to the regulator a signal in proportion to an error between the output voltage and a known reference voltage and for making the signal voltage approach zero when the load current attains its maximum value.

Yet another object of this invention is to provide in a series type transistor voltage regulator for applying to the transistor a voltage error signal in response to a variation in load voltage to correct the voltage error and for applying a current responsive signal thereto for varying the collector-to-emitter voltage to limit the dissipation of the transistor to a predetermined value upon the occurrence of an overload or short circuit.

It is also another object of this invention to provide for using inversely connected transistors in an error detection control circuit of a voltage regulator with their collector voltages and currents substantially equal, so as to minimize temperature deviations.

An important object of this invention is to provide for primarily controlling the efiective impedance of a transistor in series with a load and a source to regulate the voltage applied to the load and for limiting the collectorto-emitter voltage if the current increases sufl'iciently to comprise an over-current, so as to limit the power dissipation of the transistor.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

FIG. 1 is a schematic diagram of a series transistor voltage regulator embodying the invention in one of its forms, and

FIG. 2 is a circuit diagram in detail of the voltage regulator shown in FIG. 1.

Referring to FIG. 1 of the drawings, it will be seen that the basic circuit of the power supply comprises a constant voltage type transformer ll of the well-known term-resonant type which is connected to an alternating current force. The output of the constant voltage transformer is supplied to a suitable rectifier l2, and the output of the rectifier is passed through a filter circuit l3 which reduces the ripple voltage to a reasonable amount. A series regulator is connected between the filter l3 and a load 1e for regulating the voltage applied to the atnt load. Control of the series regulator is effected by means or an error detector circuit 17 which is connected in bridge circuit relation between a voltage divider comprising resistors R1 and R2; connected across the load circuit and a voltage divider comprising a resistor R and a Zener diode Z which is so connected across the supply circuit as to provide a substantially constant reference voltage. The error signal produced by the error detector circuit 17 in response to a variation of the load voltage is applied to the series regulator 15 through a suitable amplifier 18.

Referring to FIG. 2 it will be seen that the rectifier 12 comprises a well-known bridge type circuit of rectifier devices which may be of the germanium or other suitable type. The filter 13 comprises a condenser input filter including a choke L connected in series with the load circuit between shunt connected capacitors 2t) and 21. A resistor 19 is connected across the output to act as a dummy load for the transformer ill.

The error detector 17 comprises a pair of oppositely disposed transistors TRZ and "PR3 of the PNP type having their base electrodes 12 connected respectively to an inter mediate point between the resistors R1 and R2 of the one voltage divider by means of an adjusting potentiometer P and to an intermediate point of the other voltage divider between the resistor R and a pair of Zener diodes Z1 and Z2 which are poled to provide a substantially constant reference voltage thereacross. The emitters e of tie transistors are connected together through a current limiting resistor 22 and are connected by means of a bias resistor 23 to the positive bus 24 of the power supply so as to normally bias the transistors to conduct. Variations in the load circuit voltage with respect to the reference voltage across the Zener diodes Z1 and Z2 will therefore vary the base currents and therefore the conductivity of the transistors TRZ and TR3 in opposite senses. if the collectors c are connected to substantially the same value of voltage, temperature errors in the transistors will compensate for each other.

The amplifier 13 comprises a pair of transistors TR4 and TR5 connected in cascade. The base electrodes b are connected respectively to a negative bus 25 and to a positive bus 24- by resistors R3 and R6, while the emitters e are connected to intermediate points of voltage dividers connected across the power supply and comprising resisters R4 and R5, and RS and R7, respectively. The transistors are thereby normally biased to a state of conduction. By connecting the collector c of transistor TR3 to the base [2 of transistor TR4, the error signal is applied to the transistor TR i to vary its base current. The transistor TR4 amplifies this signal and applies it to the transistor TRS, which has its collector 0 connected to the base b of the series regulating transistor TRl. Thus an error voltage detected between the measured portion of the voltage of the load circuit 16 and the reference voltage across the Zener diodes Z1 and Z2 is amplified and applied to vary the base current of the transistor TRl so as to vary its collector-to-emitter voltage and thereby regulate the voltage applied to the load 16. The collector c of transistor TRZ is connected to the emitter e of transistor "PR4 so as to place it at a potential substantially equal to that of the collector c of transistor TR3, whereby temperature errors in the transistors TRZ and TRS are minimized.

in order to prevent damage to the transistor TRl from overcurrents, a series resistor R is connected in series with the transistor TRY. on the source side thereof. This resistor is connected by resistor R to the base electrodes b of transistor Till and an additional resistor R is connected between the base electrode and the emitter e. If the resistor R is chosen to be very much larger than the input resistance of the transistor, the following equation spanner holds, l R -l-E zfl -l-l XR Where E is the voltage across the emitter and collector of the series transistor, I is the line current, i is the signal current from the amplifier i3, and l is the base current of the transistor. This equation reduces to where B is the current amplification between the emitter and the base of the transistor. By designing the error detector and the current amplifier in such a way that the signal current is in proportion to, but of opposite polarity with respect to the error, when the voltage at the load becomes greater and is inversely proportional to it and or" the opposite polarity when the voltage at the load is reduced, when I reaches its value set as a maximum, the signal current i approaches zero and thus E approaches zero at the same time because R, is chosen to be equal or larger than R /B With the regulator in operation, a variation in the voltage across the load 16 produces a diiterential voltage across the transistors TRZ and TRS. This error voltage will increase the base current of one transistor and decrease the base current of the other, depending in which direction the voltage variation has occurred. in either case the base current of the transistor TR i will be either increased or decreased, and this signal is amplified by the transistors TRd and TRS and applied to efiect variation of the base current of the transistor TRE. This variation will be in a direction to change the emitter-tocollector voltage across the transistor TRl and correct the original variation in voltage of the load circuit 16. Should an overcurrent or short circuit occur, the voltage drop across the resistor R increases making the base electrode b more negative with respect to the emitter e. This reduces the collector-to-emitter voltage of the transistor and thus reduces the dissipation of the transistor and prevents damage thereto by reason of overheating. While constant voltage transformers have an inherent current limiting characteristic, the maximum current with a conventional type transformer input may be limited to a safe value for the transistor by properly selecting the value of R to limit the current to a value not to exceed that specified for the transistor.

Typical values of resistors used in connection with the series regulator 15 for a transistor TRl of the 2N 277 type are R, ohms, R 100 ohms, R 100 ohms. In the error detector 17, transistors TRZ and TRS are of the 2N 43 type. The transistor resistor 22, 100 ohms, resistor 23, 27,000 ohms, resistor R6, 800 ohms, resistor R1, 600 ohms, resistor R2, 2,000 ohms and a potentiometer P of 100 ohms value is used intermediate the resistors R1 and R2. In the amplifier 1S, transistor TR4 is of the 2N 167 type, while transistor TRS is of the DT 47 type, resistor R3 is 8,200 ohms, resistor R4, 150 ohms, and resistor R5 at 1,200 ohms: resistor R6, 22,000 ohms, resistor R7, 250 ohms and resistor R8, 100 ohms. A 690 microfarad condenser C is connected across the regulator at the load circuit and to supply current for very short pulse loads as well as to avoid possible high frequency isolations.

From the above description and the accompanying drawings, it will be apparent that I have provided in a imple and effective manner for closely regulating the voltage applied to a load circuit and for providing at the same time overload and short circuit protection for the regulator. A power supply embodying the regulator hereinbefore described has an output regulation of less than plus or minus one quarter of a percent for line variations of plus or minus percent and load variations of as much as 100 percent.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. it is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. in a regulator, a transistor with a known gain factor having emitter and collector electrodes for connecting a load to a voltage source and having a base electrode, an error detector connected to apply an error signal to the transistor base electrode which approaches zero when the load current exceeds a predetermined value, circuit means connected to apply a reference voltage to the error detector, additional circuit means connected to apply a predetermined portion of the voltage at the load to the error detector, impedance means connected in series with the transistor on the source side thereof, another impedance means connecting the base and emitter electrodes and having a value substantiaily greater than the input impedance of the transistor, and additional impedance means connecting the source side of the aforesaid impedance means to the base electrode to increase the basic electrode current when the load current increases, said additional impedance means bein equal to or no greater than the product of said series impedance means and the gain factor of the transistor.

2. A regulator comprising a transistor having collector and emitter electrodes connecting a load to a source of voltage and having a base electrode, means including a diode connected on the load side of the transistor to provide a substantially constant reference voltage, a voltage divider connected across the load, an error detection circuit connected between the diode and voltage divider and to the transistor to apply to the base electrode a signal in accordance with variations between the load and reference voltages until the load current exceeds a predetermined value, impedance means connected in series with the transistor and source, another impedance means connecting the base and emitter electrodes having a, value substantially greater than the input impedance of the transistor, and additional impedance means connecting the base electrode to the source to provide a direct current path, said additional impedance means having a value no greater than the product of the first-mentioned impedance means and the current gain factor of the transistor.

3. in a regulator, a transistor connected in series with a load and a source and having a predetermined input impedance and a control electrode with a current gain factor B an error detector for applying a control signal to the transistor control electrode in response to variation in the voltage at the load from a predetermined reference voltage, a first impedance R connected in series With the transistor and source to provide a direct current path, and a second impedance R connected between the control electrode and the source side of the first impedance to provide an additional direct current path and having a value no greater than R XB and a third impedance R connected between the control electrode and the load side of the transistor having a value substantially greater than the input impedance of the transistor.

4. In a regulator, a transistor having emitter and collector electrodes connecting a load to a source and having a base electrode, impedance means connected in series with the collector electrode and the source, additional impedance means connected to the base electrode and to the source side of the first-mentioned impedance means to provide a direct current path for reducing the collectorto-ernitter voltage when the load current increases above a predetermined amount and having a value substantially equal to the product of said impedance means and the current gain of the transistor, yet another impedance means connecting the base electrode and the emitter electrode and having a value substantially greater than the input impedance of the transistor, and means including an error detector responsive up to the predetermined value of a load current to a variation in voltage at the load with respect to a predetermined reference value connected to the base electrode to vary the effective impedance of said transistor to maintain a substantially constant voltage at the load below said predetermined value of load current.

References Cited in the file of this patent UNITED STATES PATENTS 2,751,549 Chase June 19, 1956 2,801,346 Rongen July 30, 1957 2,811,590 Doremus et al. Oct. 29, 1957

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