JPH01114204A - Output circuit using transistor - Google Patents

Abstract

PURPOSE:To enable the ON/OFF control of load while power consumption at the time when the load is normal is limited by providing a diode to supply a current through the load to the base of a first transistor(TR) connected to the load in series through a second TR. CONSTITUTION:At normal time that the short-circuit of the load 11 does not occur, the current for load control is supplied to the first TR 1 through a resistor r2 and the second TR 2. The diode D1, connected in relation to the second TR and the load, comes conductive when the load 11 short-circuits, and the current through the load 11 is given to the base of the first TR 1 through the second TR 2, and a large current flows in the first TR 1. But, since this current need not be a large value too much, the resistance value of the resistor r2 can be selected to be large. Thus, the power consumption by the resistor r2 and the power consumption by the first TR 1 are limited, and in addition, the large current can be flowed in the first TR 1 at the time of the short-circuit of the load.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an output circuit using a transistor that controls on/off of a load using a transistor.

BACKGROUND ART A typical prior art is shown in FIG. An NPN type transistor TR1 is connected in series to the load 1.

A resistor R1 having a small resistance value for current detection is connected in series to this load 1. Load 1 of resistor R1
A power supply voltage Vcc is applied to the terminal on the opposite side of the resistor R1, and the voltage across the resistor R1 is detected by the voltage detector 2, and both ends of the load 1 are short-circuited while the transistor TRI is conducting. When this occurs, a large current flows through the resistor R1, and when the voltage drop across the resistor R1 becomes large, the voltage detector 2 outputs a high-level signal.

To control the penis current of transistor TR,1,
An N, P N type transistor TR2 is provided. A base current is supplied to the base of the transistor TRI via a resistor R2.

The output of the voltage detector 2 is given to a processing circuit 3 realized by a microcomputer or the like.

The processing circuit 3 sends a low level signal to the base of the transistor TR2 via the resistor R3 when a low level signal is given from the voltage detector 2, that is, when the load 1 is normal and not short-circuited. give. The base of the transistor TR2 is grounded via a resistor R4, and the emitter thereof is grounded.

When a low level signal is applied from the processing circuit 3 to the base of the transistor TR2, the transistors 1 to TR2 are cut off, and a base current flows through the transistors 1 to TRI via the resistor R2. That is, transistor TRI is conductive and load 1 is energized.

When the load 1 is not short-circuited, the voltage drop across the resistor R1 is small, and the voltage detector 2 outputs a low level signal to the processing circuit 3. When both terminals of the load 1 are short-circuited, a large current flows through the resistor R1, which causes the voltage detector 2 to provide a high-level signal to the processing circuit 3. At this time, the processing circuit 3 derives a high level signal to the base of the transistor TR2.
Since 2 conducts, transistor TRI will be cut off and thus load 1 will be deenergized.

If both terminals of load 1 are short-circuited while resistor TRI is conducting, resistor R1 and transistor TR
A large current flows through I. In order to detect a large voltage drop across resistor R1 by voltage detector 2, transistor T
It is necessary to allow a large base current to flow through R1, and for this purpose it is necessary to select a small resistance value for resistor R2. However, if the resistance value of resistor R2 is chosen to be small, even in normal conditions when load 1 is not short-circuited,
A large current flows to the base of the transistor TR1 via the resistor R2, resulting in increased power consumption by the resistor R2.

In order to solve this problem, there is a prior art technique shown in FIG. This prior art is similar to the prior art shown in FIG. 3, and corresponding parts are not labeled with the same reference numerals. The prior art shown in FIG. 4 includes a plurality of transistors Ql.

The circuit configuration is such that Q2 is connected to Darling 1-. As a result, even though the current applied to the base of transistor Q2 via resistor R2 is small,
A large current can be applied to the base of transistor Q1, and therefore the current flowing through transistor Q1 can be increased.

Since the base current of transistor Q2 may be small,
The resistance value of the resistor R2 can be increased, and the power consumption by the resistor R2 can be reduced.

Problems to be Solved by the Invention A new problem with the prior art shown in FIG. 4 is that during normal operation when the load 1 is not short-circuited, the transistor Q1.

Since Q2 has a Darlington connected circuit configuration,
The voltage drop between the collector and emitter of the transistor Q1 becomes large, and the power consumption by the transistor Q1 becomes large.

SUMMARY OF THE INVENTION An object of the present invention is to provide an output circuit using transistors that is capable of controlling on/off of a load by limiting power consumption when the load is normal.

Means for Solving the Problems The present invention comprises a first transistor connected in series to a load, a second transistor for controlling the base current of the eleventh to transistors, and a resistor for supplying current to the twenty-first transistor. , a diode connected in association with the second transistor and the load, which conducts when the load is shorted, thereby directing current through the load through the second transistor to the bases of the transistors. Characteristics 1 - It is an output circuit using a transistor.

Operation In the present invention, in a normal state when there is no short circuit in the load, a current for load control can be supplied to the first L-transistor via the resistor and the L-transistor. A diode connected in conjunction with the second transistor and the load becomes conductive when the load is shorted, and when this diode becomes conductive, the current through the load is
The current is applied to the bases of the eleventh to transistor transistors through the transistor, and as a result, a large current flows through the first transistor.

Under normal conditions when the load is not short-circuited, the current flowing through the first transistor does not need to have an excessively large value, so the resistance value of the resistor can be selected to be large.

This limits the power consumption by the resistor and the power consumption by the first transistor, and also allows a large current to flow through the first transistor when the load is short-circuited.

The present invention can be widely implemented not only when a load is short-circuited but also in other cases where a large current needs to flow through the first transistor.

Embodiment FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention. A resistor s-1 having a small resistance value is connected in series to the load 11. The voltage across the resistor r1 is applied to a voltage detector 12. The voltage detector 12
In a normal state when both terminals of the load 11 are not short-circuited, a signal of low level = 7- is applied to the processing circuit 13 realized by, for example, a microcomputer, and when both terminals of the load 11 are short-circuited, When the voltage drop due to the resistor rl increases as described later and a relatively large voltage is input,
A high level signal is output to the processing circuit 13.

A transistor T r 1, which is a first transistor, is connected in series to the load 11 . The transistor Tri has its collector connected to the load 11, and this collector is connected at a connection point 14 to the anode terminal of the diode D1. Further, the emitter of the transistor T s-1 is grounded. The cathode terminal of the diode D1 is connected to the collector of the second transistor Tl-2, and a collector current is supplied to the collector through a resistor r2 having a sufficiently large resistance value.

A high level or low level signal is applied to the base of the transistor Tr2 from the processing circuit 13 via a resistor r3. This base is grounded via a resistor r4. Transistor T is connected from the emitter of transistor Tr2.
A base current is supplied to the base of ri. Manako's emitter is grounded via a resistor r5 having a sufficiently large resistance value. In this embodiment, transistors T+-1,
Both Tr2 are NPN type transistors.

In this embodiment, the base-emitter voltage VII of the transistor T1-1! , collector-emitter voltage V
cEl+Voltage V required for diode D1 to conduct
D, collector-emitter voltage V of transistor Tr2; E2 is V ci+ < Vo+ V C+:2+ V BE
...The following relationship (1) is satisfied.

Note that in the first equation, voltage V cI: + r V cE
□+VBE is each voltage value when the load 11 is not short-circuited and is normal. As a result, under normal conditions when the load 11 is not short-circuited, the diode D1 is reverse biased and does not conduct.

When the load 11 is not short-circuited, the voltage across the resistor r1 is small, and therefore the voltage detector 12 outputs a low level signal to the processing circuit 13. At this time, the processing circuit 13 provides a high level signal to the base of the transistor T r 2.

As a result, the transistor T r 2 is conductive under normal conditions, so that a base current is supplied from the emitter of the transistor Tr 2 to the base of the transistor Trl, thereby energizing the load 11 . In this case, the diode D1 is cut off, the base current applied to the transistor Tr,2 is a very small current, and the resistor r2 is selected to have a sufficiently large resistance value, so that the base current applied to the transistor Tri is very small. Although the base current generated is relatively small, the collector current is also small, so the voltage ■. 1 is small, so the power consumption of the transistor Tr1 does not increase.

When both terminals of the load 11 are short-circuited, a relatively large current is applied to the collector of the transistor T r 1. As a result, the transistor T r
The collector-emitter voltage drop of 1 becomes large, and therefore the potential of the connection point 14 becomes high. At this time, the diode D] becomes conductive, and a current is applied to the collector of the one-herald transistor T r 2 via the diode D1. As a result, the base current applied to the base of the transistor T1-1 increases, and the base current applied to the base of the transistor T1-1 increases.
A large current flows through the resistor r1, and therefore a large current flows through the resistor r1.

When a large current flows through the resistor 1-1, the voltage drop between its terminals increases, and therefore a relatively large voltage is applied to the voltage detector 12, which causes the processing circuit 1.
is given a high level signal. At this time, the processing circuit 13 derives a low level signal to the base of the transistor Tr2, thereby cutting off the transistor T1-2, and therefore, no base current is supplied to the base of the transistor T1-1.
is also cut off and the load 11 is deenergized.

The resistance value of the resistor r2 is determined by the respective voltages forming the first equation above, the power supply voltage Vcc, and the collector current of the transistor T+-1 during normal operation. and transistor T
1-1 current amplification factor 1-1. . By choosing the resistance value of the resistor r5 as expressed by the following, sufficient load driving power can be given to the load 11 in normal conditions when both terminals of the load 11 are not short-circuited. .

The collector-emitter voltage of transistor T1-1 during normal operation. , 1 is about 0.05V, and the load 1
When the collector-emitter voltage of the transistor T1-1 increases, for example, when the voltage between the collector and emitter of the transistor T1-1 is short-circuited between the two terminals of the transistor T1-1, and reaches about 5V, the diode D becomes conductive, and the short-circuit of the load 11 occurs. It will be detected.

As described above, in this embodiment, a very small current is applied to the base of the transistor Tr2 under normal conditions, and a collector current is applied to the collector of the transistor Tr2 through the resistor 1-2 having a large resistance value. Because it is
A relatively small collector current is supplied. This limits the base current of the transistor Trl, but since the collector current is relatively small and the voltage drop between the collector and emitter is sufficiently small, its power consumption is limited.

In addition, in the case 6 where both terminals of the load 11 are short-circuited, the diode D] becomes conductive, and as a result, the collector current of the transistor T r 2 increases and the transistor T
Since the base current applied to the base of r1 increases, a large current flows through the one-herald transistor Tr1, which increases the voltage drop between both terminals of the resistor r1,
The output of the voltage detector 12 becomes high level, and a short circuit between both terminals of the load 11 is detected.

FIG. 2 is a block diagram showing the basic configuration of another embodiment of the present invention. This embodiment is similar to the above-described first embodiment, and the same reference numerals are used to indicate the same functions. This embodiment is based on the above-mentioned first embodiment.
It is constructed using P-type transistors.

During normal operation when both terminals of load 11 are not short-circuited,
A relatively small voltage is applied to the voltage detector 12, and therefore the voltage detector 12 outputs a low level signal to the processing circuit 13. When the processing circuit 13 is supplied with a low level signal from the voltage detector 12, the processing circuit 13 outputs a low level signal to the base of the transistor T r 4, which is a PNP type transistor and is a 21st transistor, via a resistor r3. The signal is derived.

When the voltage detector [2] outputs a high level signal, the processing circuit 13 derives a high level signal from the bases of the transistors 1 to TI-4.

The emitters of the transistors 1 to T1-4 are PNP transistors, and are connected to the base of the transistor Tl-3, which is the first transistor.
A current is supplied to the emitter of r3 from the power supply.

Further, the collector of the transistor T r 4 and the collectors of the transistors T r 1 to T r 3 are connected through a diode D1, and the diode D1 is cut off during normal operation when both terminals of the load 11 are not short-circuited. There is.

Voltage detector 1 under normal conditions when load 11 is not short-circuited
2 derives a low level signal as described above, the base of the transistor T r 4 is given a low level signal from the processing circuit 13, and therefore the transistor T1-4 is conductive. , whereby the transistors T1-3 are also conductive. This results in load 1
1 is supplied with a drive current from the power supply through the transistor Tr3.

When both terminals of the load 11 are short-circuited, a voltage drop across the transistor Tr'3 increases the voltage between the collector and emitter of the transistor Tr'3. Therefore, the potential at the connection point 15 connecting the collectors of the transistors T1, r3 and the cathode of the diode D1 decreases, thereby making the diode D1 conductive.

When the diode D1 becomes conductive, the load 11 receives a current from the transistor T1-3 as well as a current from the transistor T1-3.
From the base of 1-3 to the emitter of transistor Tl-4,
A current is also applied via the collector and the diode D1. As a result, a large current flows through the resistor r1, and therefore a relatively large voltage is input to the voltage detector 12, and its output becomes high level. As a result, the processing circuit 13
4, thus transistor T r4 is cut off and transistor T r
3 will also be blocked. This causes the load 11 to be deenergized.

As described above, this embodiment is characterized in that the first embodiment described above is constructed using PNP type transistors, and this embodiment can also obtain the same effect as the first embodiment described above. .

Although the above embodiment describes the case where a short circuit in the load is detected and the load is deenergized, the present invention requires a large current to flow through the first transistors (T r 1 , T r 3 ). It is widely practiced in various cases.

Effects As described above, according to the present invention, the power consumption of the load during normal operation is limited, and moreover, the load can be controlled on/off. Furthermore, since the power consumption of the first transistor during normal operation is small, heat generation during normal load operation can also be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of one embodiment of the present invention, FIG. 2 is a block diagram showing the basic configuration of another embodiment of the present invention, and FIG. 3 is a typical prior art. FIG. 4 is a block diagram showing another prior art. 11-...Load, T r 1 , T r 2 , T
r3, Tr4...transistor, rl,
1-2.1-3. r4. +-5...Resistance, Dl...
Diode agent Patent attorney Number of strokes Keiichi Figure 1 Figure 3 Figure 4

Claims (1)

[Scope of Claims] A first transistor connected in series to a load, a second transistor that controls the base current of the first transistor, a resistor that supplies current to the second transistor, and a connection between the second transistor and the load. a diode connected in association with the load, which conducts when the load is shorted, thereby directing current through the load through the second transistor to the base of the first transistor. Output circuit used.