JPH03136112A - Regulated power supply circuit - Google Patents

Abstract

PURPOSE:To improve the accuracy for protecting an overcurrent by detecting a fact that an excessive current flows between an emitter and a collector of a PNP type transistor, and limiting a base current by a control means. CONSTITUTION:The circuit is constituted of a control circuit 2 being a control means for controlling a base current of a PNP type transistor Tr1 and a protect ing circuit 3 provided with various protecting function. The protecting circuit 3 is provided with an overcurrent protecting circuit 8, this overcurrent protecting circuit 8 detects a potential difference across a resistance R1, and when this potential difference reaches an overcurrent detection voltage, the base current of the transistor Tr1 is limited by limiting a current flowing to a buffer ampli fier 7. Accordingly, even if there is a variance in a DC current amplification factor of the transistor, an output current is limited without being influenced thereby. In such a way, the overcurrent protection is executed with high accu racy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a series control type stabilized power supply circuit using a PNP transistor as a voltage control element.

[Conventional technology]

For example, as shown in FIG. 4, a conventional series control type stabilized power supply circuit includes NPN transistors Tr3. is used. Transistor Tr3.
The collector is connected to the input terminal (2), the emitter is connected to the base of the transistor Tr3□, and the output terminal (2) is connected via the resistor R3+. The base is connected to the output terminal of the differential amplifier 31 and the transistor T.
r32 collector. transistor T
The emitter of rB is the resistor R31 and the output terminal ■. A current source 32 is provided between the collector of the transistor Tr, and the collector of the transistor Tr. The above resistance R21
The transistor Tr,2 constitutes an overcurrent protection circuit 33 in the stabilized power supply circuit.

A voltage divider circuit 34 in which resistors R3z-R, 3 are connected in series.
Is resistance R3! One end is the output terminal■. , one end of resistor R33 is grounded, and the output terminal ■. The output voltage appearing at is divided by the voltage division ratio of resistors Rff2 and R33 and fed back to the differential amplifier 31. Further, the differential amplifier 31 has an inverting input terminal connected to a resistor R0 and a resistor R0.
33, and its non-inverting input terminal is connected to a reference voltage source 35.

In the above stabilized power supply circuit, the transistors Tr,
is turned on when a base current is supplied by the current source 32, causing a current to flow between the collector and emitter. transistor T
r3. output terminal v0 from the emitter of
The output voltage appearing at is divided by the voltage dividing circuit 34 and inputted to the differential amplifier 31 as a feedback voltage. Differential amplifier 3
1 is a transistor Tr so that the feedback voltage becomes equal to a constant reference voltage given by the reference voltage source 35;

control the base current of Therefore, the output voltage is maintained at a constant voltage according to the reference voltage of the reference voltage source 35.

Also, if the output current increases due to overload or output short circuit,
The voltage generated across the resistor R31 rises accordingly. When this voltage reaches approximately 0.7 V, transistor Tr3. A part of the current supplied to the base of transistor Tr32 flows between the collector and emitter of transistor Tr32. This reduces the current flowing into the bases of transistors Tr, , and transistors Tr3. The current flowing between the collector and emitter of is limited. The transistor Tr and the load (not shown) are protected from overcurrent by limiting the output current in this manner.

By the way, the above stabilized power supply circuit includes a transistor Tr.
Although the voltage can be held constant with 3+,
For this reason, it is necessary to ensure a voltage difference of 3 V or more between input and output, and this has the disadvantage that efficiency decreases due to loss caused by this voltage difference. Therefore, in recent years, as shown in FIG.
A stabilized power supply circuit that can perform voltage control with a voltage difference as small as below has been devised and is beginning to become popular.

However, in this stabilized power supply circuit, the resistor R31 of the overcurrent protection circuit 33 is replaced by a transistor Tr for overcurrent detection.
If it is connected in series to the emitter of :++, the voltage difference between the input and output will increase due to the voltage drop caused by this resistance, and the above advantages will be lost.

Therefore, in the stabilized power supply circuit described below, the arrangement of the overcurrent protection circuit 33 is taken into consideration, and the above-mentioned problems are solved. For convenience of explanation, members having the same functions as those of the stabilized power supply circuit shown in FIG. 4 are denoted by the same reference numerals.

As shown in FIG. 5, the transistor Trzs as a series control element has its emitter connected to the input terminal V, its base connected to the collectors of the transistors Tr, ..., Tr, and s, and the collector connected to the output terminal V. Terminal ■. and is grounded via a voltage dividing circuit 34 made up of resistors R3Z and R3. The differential amplifier 31 has an inverting input terminal connected to the connection point between the resistor R8 and the resistor R33, a non-inverting input terminal connected to the reference voltage source 35, and an output terminal connected to the base of the transistor Tr and the overcurrent. It is connected to the collector of the transistor Tr32 in the protection circuit 33. The reference voltage source 35 has an input terminal V
, and is grounded to obtain a constant reference voltage from the input voltage. Transistor Tr3. The emitter is connected to the base of the transistor Trzs, and the transistors Tr, . . . form a Darlington circuit. Transistor Tr3. The emitter is grounded via the resistor R31 of the overcurrent protection circuit 33, and is also connected to the base of the transistor Tr, +2, and the emitter and terminal of the transistor Trsz are grounded.

In the above stabilized power supply circuit, when the output current increases, the base current of the transistor Tr33 increases.
It flows to the resistor R31 via a·Tr, . Then, when the voltage generated across this resistor R31 reaches approximately 0.7 V, the transistor Tr+
□ turns on and reduces the base current of transistor Tr3°. This reduces the base current of transistor Tr,3 and limits the current flowing between the collector and emitter of transistor Tr, .

[Problem to be solved by the invention]

However, in the above stabilized power supply circuit, the transistor T
No matter how accurately the base currents of r, , , etc. are controlled, the output current limit level determined by the overcurrent protection circuit 33 will vary widely due to variations in the DC current amplification factor of the transistor Tr33. However, there was a problem in that the accuracy of overcurrent protection decreased.

[Means to solve the problem]

In order to solve the above problems, the stabilized power supply circuit according to the present invention uses a PN as a series control element to control the input voltage.
In a stabilized power supply circuit including a P-type transistor and a control means for controlling the base current of the PNP-type transistor so that the negative feedback output voltage becomes equal to a constant reference voltage, the PNP-type transistor has an emitter A current detection resistor for detecting the current flowing between the collectors is connected in series with the emitter, and the overcurrent detection voltage of this current detection resistor is sufficiently lower than the emitter-collector saturation voltage of the PNP transistor. On the other hand, the potential difference between both ends of the current detection resistor is used as an overcurrent detection voltage that detects that an excessive current is flowing through the current detection resistor. The present invention is characterized in that it includes current limiting means that limits the base current of the PNP transistor controlled by the control means when the current reaches .

[For production]

In the above configuration, when performing normal voltage control, the input voltage is a PNP whose base current is controlled by the control means.
It is controlled by a type transistor and output as a constant voltage according to the reference voltage.

On the other hand, as the current flowing between the emitter and collector of the PNP transistor increases, the potential difference across the current detection resistor increases, but when this potential difference reaches the overcurrent detection voltage, the PNP transistor controlled by the control means The base current is limited by the current limiting means and kept substantially constant, thereby protecting the PNP transistor and the load from overcurrent.

In the above series of operations, since the current detection resistor is connected in series to the emitter of the PNP transistor,
Current detection will be performed on the input side of the PNP transistor. Therefore, even if there are variations in the direct current amplification factors of the PNP transistors, the output current can be limited by the current limiting means without being affected by the variation, and overcurrent protection can be performed with high precision. In addition, the resistance value of the current detection resistor is set so that the overcurrent detection voltage that operates the current limiting means is sufficiently lower than the saturation voltage of the PNP transistor. The voltage difference between outputs does not increase. Therefore, the advantage of the stabilized power supply circuit using PNP transistors, which is that voltage control is possible with a small voltage difference between input and output, is not lost. Furthermore, since the current detection resistor can be selected from different resistance values, it is possible to set the overcurrent detection voltage differently, changing or fine-tuning the level of output current that is detected as an overcurrent. can do.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 1, the stabilized power supply circuit according to this embodiment includes a DC control element l including a transistor Tr as a PNP transistor, and a control circuit 2 as a control means for controlling the base current of the transistor Tr+. and a protection circuit 3 having various protection functions. The transistor Tr+ of the series control element 1 has a base connected to the output terminal of the buffer amplifier 7 in the control circuit 2 and an output terminal of the protection circuit 3, and a collector connected to the output terminal (2) in the stabilized power supply circuit. It is connected to the.

The series control element 1 is provided with a resistor R1 as a current detection resistor in addition to the transistor Tr.
1 has one end connected to the input terminal 1 in the stabilized power supply circuit, and the other end connected to the emitter of the transistor Tr+. The resistor R1 is set to a resistance value such that the potential difference generated between both ends when an excessive current flows, that is, the overcurrent detection voltage, is sufficiently lower than the collector-emitter saturation voltage of the transistor Tr. For example, if the above collector-emitter saturation voltage is 0.
In the case of 5■, the potential difference generated across the resistor R1 is 0.1V.
If the resistance value is set as follows and an overcurrent IA flows through the resistor R, the resistance value will be 0.1Ω or less. As described later, different resistance values can be selected for the resistor R.

The control circuit 2 includes a voltage divider circuit 4 that feeds back an output voltage to the differential amplifier 6, a reference voltage tA5 that provides a constant reference voltage to the differential amplifier 6, and a voltage divider circuit 4 that provides a constant reference voltage to the differential amplifier 6. The differential amplifier 6 includes a differential amplifier 6 that controls the base current of the transistor Tr, and a buffer amplifier 7 that stably controls the differential amplifier 6. In this control circuit 2, the voltage dividing circuit 4 includes a resistor R2
・R3 are connected in series, one end of resistor R2 is connected to the collector of transistor Tr+, and resistor R
One end of 3 is grounded. The differential amplifier 6 has an inverting input terminal connected to the connection point between the resistors R2 and R1, a non-inverting input terminal connected to the output terminal of the reference voltage source 5, and an output terminal connected to the input terminal of the buffer amplifier 7. It is connected to the. The reference voltage source 5 is connected to the input terminal (2) and grounded, so that a constant reference voltage is obtained from the input voltage.

The protection circuit 3 includes an overcurrent protection circuit 8 composed of a differential amplifier, and also includes various protection functions such as overvoltage protection and overheating protection as necessary. The overcurrent 1 protection circuit 8 has an inverting input terminal connected to the connection point between the emitter of the transistor Tr in the series control element 1 and the resistor R1, a non-inverting input terminal connected to the input terminal 2, and an output terminal is connected to the input terminal of the buffer amplifier 7. This overcurrent protection circuit 8 detects the potential difference between both ends of the resistor RI, and when this potential difference reaches the overcurrent detection voltage, limits the current flowing to the buffer amplifier 7, thereby limiting the base current of the transistor Tr+. It has become.

Here, the structure of the series control element 1 will be explained.

As shown in FIG. 2, an N-type epitaxial layer 10 as a base is formed on a P-type substrate 9 as a collector, and a diffusion layer 11 as an emitter is further formed. A transistor Tr+ is configured.Furthermore, on the upper part of the epitaxial layer 10, a diffusion layer 1 is formed.
A resistor layer 12 made of an N+ region is formed in contact with the resistor R1 in the series control element 1, and a resistor R1 in the series control element 1 is configured. Furthermore, a buried layer 13 made of an N' region is provided between the substrate 9 and the epitaxial layer 10 so that another transistor is not formed by the resistance layer 12. Then, metal wiring layers 14...14 are provided for connection between the diffusion layer 11, the resistance layer 12, and the outside, while Si is used for insulation between the metal wiring layers 14...14.
Insulating layers 15...15 made of O□ are provided,
These metal wiring layers 14...14 and insulating layers 15...
... 15, a protective layer 16 is formed.

Next, the configuration of the resistor R in the series control element 1 will be explained.

As shown in FIG. 3(a), the resistor R is constructed by connecting a plurality of resistors R1 to RI5 having different resistance values in parallel. Actually, as shown in FIG. 3(b), the resistors R11 to RI5 correspond to the respective resistor patterns 17.
21, and the resistor R1 is formed by connecting these resistor patterns 17 to 21 to a metal wiring pattern 23 through contact windows 22, . . . . The resistance patterns 17 to 3 4 21 are made up of the resistance layer 12, and the metal wiring pattern 23 is made up of the metal wiring layers 14...14. Further, the resistor R1 is connected to the metal wiring pattern 23.
Cutting portions 23a to 23e are provided at the portions that branch to connect to the resistor patterns 17 to 21, and by trimming any of the cutting portions 23a to 23e with a laser or the like, the resistors R1 to R15 are The resistance value can be selected by changing the connection combination.

In the above configuration, the input voltage input from the input terminal V passes through the transistor Tr+ to the output terminal V. This output voltage appears as an output voltage, and this output voltage is divided by the voltage dividing circuit 4 and inputted to the differential amplifier 6 as a feedback voltage. At this time, when the input voltage fluctuates, the feedback voltage also fluctuates, but since the differential amplifier 6 controls the base current of the transistor Tr so that the feedback voltage is equal to the reference voltage of the reference voltage source 5, the transistor Tr controls the input voltage so that it cancels out fluctuations in the input voltage. This will keep the output voltage constant.

On the other hand, when the output current increases due to an overload or an output short circuit, the potential difference between both ends of the resistor R3 increases. When this potential difference reaches the overcurrent detection voltage, the overcurrent protection circuit 8 operates to limit the base current of the transistor Tr+. As a result, the output current is limited and held constant, and the transistor Tr and a load (not shown) are protected from overcurrent.

In the above operation, the resistor R3 is the transistor Tr,
Because it is connected in series to the emitter of transistor Tr+, even if there are variations in the DC current amplification factor of transistor Tr+,
The output current can be limited by the overcurrent protection circuit 8 without being affected by this. In addition, the resistor R1 is set to a resistance value such that the overcurrent detection voltage appearing at both ends is sufficiently lower than the collector-emitter saturation voltage of the transistor Tr+, so that the voltage drop due to the resistor R1 is negligible. The voltage difference between input and output can be suppressed to about the saturation voltage between the emitter and collector 5 of the transistor Tr. Furthermore, the resistance R
Since one resistance value can be selected by trimming, different overcurrent detection voltages can be set, and the level of output current detected as overcurrent detection can be changed or finely adjusted.

〔Effect of the invention〕

As described above, the stabilized power supply circuit according to the present invention includes a PNP type transistor as a series control element that controls an input voltage, and a PNP type transistor that functions as a series control element to control an input voltage, and a PNP type transistor that functions as a series control element to control an input voltage. In a stabilized power supply circuit equipped with a control means for controlling a base current, a PNP
A current detection resistor that detects the current flowing between the emitter and the collector is connected in series to the emitter of the type transistor, and this current detection resistor is connected in series to the emitter when the overcurrent detection voltage is P.
The resistance value is set to a voltage that is sufficiently lower than the emitter-collector saturation voltage of the NP transistor, and different resistance values can be selected. The configuration includes current limiting means that limits the base current of the PNP transistor controlled by the control means when the overcurrent detection voltage reaches an overcurrent detection voltage that detects that an excessive current is flowing.

As a result, the current is detected on the input side of the PNP transistor, so even if there is variation in the DC current amplification factor of the PNP transistor, the output current can be limited without being affected by it. Current protection can be performed with high precision. In addition, the voltage difference between the input and output hardly increases due to the voltage drop caused by the current detection resistor.
The advantage of the stabilized power supply circuit using PNP transistors, which is that voltage control is possible with a small voltage difference between input and output, is not lost. Furthermore, by selecting the resistance value of the current detection resistor, the level of the output current detected as overcurrent detection can be changed or finely adjusted. Therefore, due to the above-described effects, it is possible to provide the stabilized power supply circuit with a more advanced overcurrent protection function.

7 8

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention. FIG. 1 is a circuit diagram showing the configuration of a stabilized power supply circuit. FIG. 2 is a partial sectional view showing the structure of the DC control element. FIG. 3(a) is a circuit diagram showing the configuration of resistors in the DC control element. FIG. 3(b) is a plan view showing a specific example of the structure of the resistor. FIGS. 4 and 5 show conventional examples. FIG. 4 is a circuit diagram showing the configuration of the stabilized power supply circuit. FIG. 5 is a circuit diagram showing the configuration of another stabilized power supply circuit. 2 is a control circuit (control means), 8 is an overcurrent protection circuit (current limiting means), R1 is a resistor (current detection resistor), and Tr+ is a transistor (PNP type transistor).

Claims (1)

[Claims] 1. A PNP transistor as a series control element that controls an input voltage, and a control means that controls the base current of the PNP transistor so that the negative feedback output voltage becomes equal to a constant reference voltage. In the stabilized power supply circuit, the PNP transistor has a current detection resistor connected in series to the emitter to detect the current flowing between the emitter and the collector, and this current detection resistor is connected to the overcurrent detection voltage. is set to a resistance value that is sufficiently lower than the emitter-collector saturation voltage of the PNP transistor,
When the potential difference across the current detection resistor reaches an overcurrent detection voltage that detects that an excessive current is flowing through the current detection resistor, the control means controls the current detection resistor. 1. A power supply circuit comprising current limiting means for limiting the base current of a PNP transistor.