US3079543A

US3079543A - Overload and short circuit protector for transistor voltage regulator

Info

Publication number: US3079543A
Application number: US18922A
Authority: US
Inventors: David L Decker
Original assignee: Collins Radio Co
Current assignee: Collins Radio Co
Priority date: 1960-03-31
Filing date: 1960-03-31
Publication date: 1963-02-26
Anticipated expiration: 1980-02-26

Description

Feb. 26, 1963 D. L. DECKER 3,079,543

OVERLOAD AND SHORT CIRCUIT PROTECTOR FOR TRANSISTOR VOLTAGE REGULATOR Filed March 31, 1960 SIGMA:

FIEI

5) awm.

INVENTOR. 0/: VIP A. Dfit'AE/P BY Q/(w 14w OVERLOAD Ann Iowa Filed Mar. 31,-196tt, SenNo. 18,922 1 Claim. (U. 323-22) This invention relates to an overload and short circuit protector device and more particularly to a device for use in voltage and current regulators of the type utilizing semi-conductors to protect the components of the regulator against damage due to heavy overloads or shorts in the output circuit of the regulator.

Voltage and current regulators are well knownin the art and in the past commonly utilized at least one power amplifying tube to provide the desired regulated output. While it was desirable to protect the regulator, and es pecially the power tube, against damage, which sometimes required the use of protector devices, thenecessity of such aprotector device has been accented in recent years due to the developmentand use of semi-conductors in voltage and current regulators. This is due'to the fact that a semi-conductor is far more susceptible to severe damage due to the heat produced during excessive conduction of current than is a vacuum tube. 7

various protector devices have heretofore been suggested and utilized to protect the components, and es pecially the semi-conductors, used in the voltage and current reguilato-r against damage due to a short in the output circuit since this obviously would cause heavy current conduction through the regulator and damage its components severely in a very short time.

Providing a protector device that merely guards against a short in the output circuit, however, is not sufficient, of itself, to adequately protect a voltage and current regulator since a short'in the output circuit is only one possible occurrence which can cause damage to the regulator. An additional, and very real possibility of damage, also exists in the event that a heavy overload is connected into the output circuit of the regulator, since this too will cause excessive current conductiontherethrough.

It is therefore an object of'this invention to provide simple, yet reliable means to protect a voltage and current regulator against damage due to either a short or a heavy'overload in the output circuit of the regulator.

It is another object of this invention to'provide means responsive to the regulator output voltage to bias the power amplifier of the regulator to cutoff whenever a heavy overload or short appears in the output circuit of the regulator to thereby protect said regulator against damage due to excessive current flow therethrough.

More particularly it is an object of this invention to provide protector means including a transistor normally biased to cutofi so that said means is operable only when the regulated output voltage of the regulator drops below apredetermined and preset level to thereafter preclude further conduction of current through the regulator.

'It is still another object of this invention to provide protector means operable to preclude current flow through the regulator after a heavy overload or short is connected into the output circuit of such a regulator and to maintain said regulator in its inoperative state until such time as the heavy overload or short is removed from the output circuit and the input signal to the regulator is thereafter removed and then reapplied.

With these and other objects in view which will become apparent to one skilled in the art as the description proceeds, this invention resides in the novel construction, combination and arrangementcf parts substantially as hereinafter described and more particularly defined by arrests Patented Feb. 26, 1963 the appended claims, it being. understood that such changes in the precise embodiments of the herein disclosed information may be submitted as come within the scope of the claims.

The accompanying drawings illustrate two complete examples of two embodiments of the invention constructed according to the best mode so far devised for the practical application of the principles'thereof, and in which:

FIGURE '1 is a schematic circuit diagram of a voltage and current regulator having the protector device-of this invention incorporated and illustrated as a part thereof; and" FIGURE 2 is a schematic circuit diagram of a modified voltage and'current regulator having. a modifiedprotector device incorporated and illustrated as a part thereof.

Referring now to the'd'rawings in'which'like numerals have been used to identify like characters throughout, the numeral 3' designates generally a voltage and current regulator, which may be of conventional type, in which the protector device 4" of this invention may be utilized to protect the regulatoragainst damage should a short circuit or a heavy overload be" connectcd'into its output circuit.

As shown inPIGUR'E 1, Voltage and current regulating device 3 may include a power amplifier 6, which is preferably a transistor, andsignal sampling means'7 to regulate the conduction of transistor 6 by controlling the bias thereof.

As shown in the drawings, transistor 6 may be of'the PNPtype' (as shown in FIGURE 1) or of the NPN' type (as shown in FIGURE 2 and designated with the numeral 1%) so long as other circuitry of the regulator is clfianged accordingly as brought outmorte'fully hereina ter.

As shown in FIGURE 1, transistor 6 may have its emitter connected with the positive output of a source of unregulated direct current signal 8 by means of a lead it its collector connected with a variable output circuit load 12 by means of regulated output circuit lead 14, and its base connected with the negative output of source 8 through bias resistor 16' by means of leads 18 and 15 which are connected to ends 2% and 21, respectively of bias resistor'16. To complete the output circuit, load l2 may also be connected to lead 19 by means of lead 22. If desired, stabilizing-capacitor 23" may be connected across output'leads l4 and 22 to prevent'oscillation.

Signal sampling means 7, as above-stated, regulates thebias on transistor 6' to therebycontrol the conduction of-the same so that a regulated output is supplied by the regulator. As shown by the drawings, signal sampl-ing means '7 includes a voltage divider 2E which may include a fixed resistor 26 and a variable resistor 27 serially connected tbetween leads 14 an'd22. As shown in FIGURE 1, the variable tap-23 of resistor 27 may be connected to the b'aseof atransistor'iidof'the NPN type through current limiting resistor Sland diode 32, which is, or course, connected so that low resistance-is ofiered to base current flow.

The emitter of'transistor"3tt is connected'to leads 19 and 22 through a breakdown junction or Zener diode 35, which diode is also connected to input lead 10 through bias resistor 36. Diode 35is orientated so that the voltage applied to the emitter of-transistor 30 is maintained at the breakdown voltage of the diode.

The collector of transistor 36 isconnected tothe base of a 'PNP' type transistor 4t through cur-rent limiting resistor 41 while the collector of transistor 40 is, in'turn, connected to-side 200i resistor 16,- which, as'brought out hereinbefore, provides bias for transistor 6. The emitter of transistor 4% is directly connected to input lead'luby means of

leads

45 and 46, and-resistor 1'6 is'therefoi'e aosaeae d) also in the output circuit of transistor 4t Forward bias for transistor 4% is provided by resistor 48 which connects the emitter and base of said transistor.

The protector device 4 of this invention includes a voltage divider 53 which may include fixed resistance 54, and variable resistance 56, the variable tap 57 of which may be directly connected to the base of a PNP type transistor 69, as shown in FIGURE 1. The emitter of transister as may be connected with input lead it} through resistor 52 and connecting

leads

46 and 63. A breakdown junction or Zener diode 64 is connected between

leads

19 and 63 to maintain the voltage of the emitter of transistor ed at the breakdown voltage of the diode. In addition, a capacitor 65 is connected in parallel with diode 6d, and this capacitor along with resistor 62 provides an RC. time constant the purpose of which is hereinafter brought out.

The collector of transistor 6%} is connected to the base of transistor 30 through limiting resistor 66 and due to the orientation of diode 32, collector circuit current must be applied to the base of transistor 3%, the result of which is to bias transistor 6 to cutoff as brought out hereinbelow. in operation, the voltage and current regulator shown in FIGURE I normally operates in the following manner. Assuming that the load 12 is increased by an amount not considered excessive, the voltage potential between

leads

14 and 22 will decrease thus decreasing the voltage drop across voltage divider 25. This means that a lower, or more negative, voltage is impressed upon the base of transistor 39, and since it is a transistor of the NPN type, conduction inthe base circuit decreases causing a corresponding decrease in conduction in the collector circuit. This decrease in current flow, of course, causes a decrease in the voltage drop across bias resistor 48 which is in the collector circuit of transistor 30. The decreased voltage drop across resistor 43 causes the emitter of transistor at} to become less positive with respect to the base so that conduction in the base-emitter circuit of PNP type tran sister 40 is decreased. The collector current of transistor 4t) will, of course, likewise be decreased, and since resistor 16, which provides bias for transistor 6, is also in the collector circuit of transistor 40, there will be a decrease in the voltage dropped across this resistor. This decreased voltage drop across resistor 16 is impressed upon the input circuit of transistor 6 so that the base of transistor 6 becomes less positive, or more negative, than the emitter, and results in increased conduction by transistor 6.

When the output voltage of the regulator is substantially returned to its former level, the bias of transistor d, which is controlled by the output level, will, of course, be altered accordingly to decrease the conduction of transistor 6 to maintain the output at a predetermined regulated level.

The protector device of this invention is normally inoperative during the above described normal operation of the regulator since this protective network is needed only in case of a heavy overload or a short in the output circuit. This is accomplished by biasing transistor dtl to cutofi for normal operation by adjusting variable tap 57 of resistor 56 (which is a part of voltage divider 53) so that a higher positive voltage is impressed upon the base of PNP type transistor do than is present on the emitter. Thus the protector device can be preset to become operative at any predetermined output potential by adjusting variable tap 57.

From the foregoing it will be appreciated that the protector device of this invention will be inoperative until the potential between output leads lid and 22 decreases to a value that causes the voltage impressed upon the .base of transistor as to be more negative than the emitter voltage.

When, for example, output circuit load 12. is increased to such an extent that it constitutes a heavy overload, the potential between leads l4 and 22 will be decreased causing a corresponding decrease in voltage drop across

dividers

25 and 53. It is to be noted that the same decrease in voltage drop across these dividers occurs in the case of a short circuit although it is usually much more pronounced and acts to short out the dividers completely. When such a heavy overload or short appears in the output circuit of the regulator, the regulator normally tries to supply the necessary voltage to return the output to its former level. This, of course, can cause excessive conduction and severe damage through excessive heat to the components of the regulator and especially to the power transistor. The protector device of this invention prevents this excessive conduction in the -following manner.

When a heavy overload or a short first appears in the output circuit, transistor 6d, which, as brought out hereinbeiore is normally biased to cutoff, will immediately start to conduct because of the decreased voltage impressed upon its base to make it negative with respect to the emitter. Collector current from transistor so is applied to the base of transistor 3h causing the base of NPN type transistor 34? to become more positive with respect to the emitter. This causes transistor 3d to conduct at an increased rate and causes a greater voltage drop across resistor 48, which, in turn causes the emitter of PNP type transistor 40 to become more positive with respect to the base. This causes transistor 4% to conduct at an increased rate and causes a greater voltage drop across resistor 21 which, in turn, causes a greater voltage to be impressed on the base of transistor 6 biasing the same to cutoff and thereby rendering the regulator inoperative.

When protector device 4 is caused to operate and bias transistor 6 to cutofi, the voltage regulator will remain inoperative until such time as the input voltage is removed from the regulator. When this voltage is reapplied the R.C. time constant provided by resistor 62 and capacitor 65 is such so as to allow the output to build up and bias transistor 64] to cutoff before full voltage is applied to the emitter of transistor 69. If, of course, the heavy overload or short circuit has not been removed, however, the protective device will again immediately bias transistor s to cutoff and render the regulator inoperative.

It is to be appreciated that the protector device of this invention may be modified by using a transistor of the NPN type, if the circuitry of the voltage and current regulator in which it is utilized so requires, without departing from the spirit or scope of this invention.

FIGURE 2 illustrates, for example, a voltage and current regulator 193 utilizing a transistor of the NPN type in place of PNP type transistors 6 and 40 and a PNP type transistor in place of NPN type transistor 3b as shown in FIGURE 1. The protector device 1% in this case may utilize a transistor of the NPN type in place of the PNP type transistor 60 as shown in FIGURE 1.

As shown in FIGURE 2, a negative lead 11% is connected to the emitter of transistor 1% while positive lead 119 is connected to the emitter of transistor 1% while positive lead 119 is connected to the base of transistor 1%. In addition, lead its is a negative output circuit lead and is connected with the collector of transistor ltld, while lead 12 2 is the positive output circuit lead and is connected to lead 119. It can therefore be readily appreciated that the circuit will operate in much the same manner as that of FIGURE 1, but the voltage polarities will be reversed. For this reason,

Zener diodes

35 and 64 must, of course, be reversed and the same is true of diode 32..

in operation, when an increased load, not considered excessive, is applied to output circuit load 12, the voltage potential between leads A l and 122 will be decreased. This, of course, causes a decrease in voltage drop across voltage divider 25 and causes a decrease in the voltage appliedtothe base of PNP type transistor 13d. it is to be-remembered, however, that the emitter of transistor 13% is also negative so that a decrease in negative voltage on the base decreases the difference in potential between the emitter and base. This causes a decrease in conduction in the input circuit and will, therefore, decrease current conduction in the collector circuit. This causes a decrease in the voltage drop across bias resistor 48 and because of the polarity of this voltage drop makes the emitter of NPN type transistor 140' less negative with respect to the base and causes decreased conduction in its output circuit. This, in turn, causes a decreased voltage drop across bias resistor 16 and, due to the polarity of this voltage drop, the voltage impressed upon the base of NPN type transistor 106 makes the base less negative, or more positive, with respect to the emitter and causes increased conduction in the output circuit to return the voltage potential between output leads 114 to 122 to the desired level.

If, however, a short or a heavy overload is connected into the output circuit of the regulator, protector device 104, which has been modified by replacing the PNP type transistor shown in FIGURE 1 with a transistor of the NPN type as brought out hereinabove, will conduct to bias transistor 106 to cutotf and render the regulator inoperative. This is accomplished by applying the collector current of transistor 160 to the base of transistor 130 in the same manner as that described in connection with the protector device shown in FIGURE 1. This impressed voltage causes increased conduction in PNP type transistor 130, which in turn causes increased conduction in transistor 140. The resulting increased voltage drop across resistor 16 impresses a more negative voltage on the base of NPN type transmitter 106 and causes the same to be biased to cutoff.

As described in connection with FIGURE 1, the regulator shown in FIGURE 2 will likewise remain in a nonoperative state until such time as the input signal from source 9 is removed from the input leads 110 and 119 and then reapplied since the emitter of transistor 160 will remain more negative than the base until the signal is first removed from this emitter.

While two specific examples have been shown and illustrated herein to adapt the protector device of this invention to a specific voltage and current regulator, it is to be appreciated, of course, that the protector device of this invention might be modified to meet other specific circuitry requirements without departing from the spirit or scope of this invention.

In view of the foregoing it should be obvious to those skilled in the art that the protector device of this invention provides simple yet reliable means for protecting a voltage and current regulator against damage to its components from excessive conduction through the regulator due to a heavy overload or a short in the output circuit of the regulator.

What is claimed as my invention is:

A transistorized voltage and current regulating device of the type having output overload and short circuit protector means and requiring no operating power other than that from an unregulated D.C. source, said regulating device comprising: power amplifying means having an input circuit and an output circuit, said input circuit including resistance means for biasing said power amplifying means and said output circuit including voltage divider means; means adapting said input circuit for connection with an unregulated D.C. power source; means adapting said output circuit for connection with a load so that said load is in parallel with said voltage divider means; output voltage sampling means connected between said voltage divider means and said resistance means to determine and regulate the bias on said power amplifying means; a transistor having an input electrode, a control electrode, and an output electrode; a Zener diode connected with said input circuit and with said input electrode for assuring that a constant voltage is applied to said input electrode; means for applying direct voltage from said voltage divider means to said control electrode to normally bias said transistor to cutoff, said transistor remaining in a nonconductive state until a load connected with said output circuit draws excessive current causing said transistor to conduct, said transistor then remaining in said conductive state until the power from the unregulated source is removed; means connecting said output electrode with said voltage sampling means for coupling an output signal thereto while said transistor is in a conductive state to bias said power amplifying means to cutoff; and an RC. network including a capacitor in parallel with said Zener diode and a resistor having one end connected to said input electrode and the other end connected to said input circuit whereby said R.C. network prevents the application of breakdown voltage to the input electrode of said transistor for a predetermined time interval immediately after power from the unregulated source is coupled to said regulating device to thereby allow cutofi bias to first be impressed upon the control electrode of said transistor.

Harrison Dec. 1, 1959 Norris et a1. Jan. 26, 1960