JPH0317122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current supply device having an output current limiting function, and provides a current supply device having an extremely simple configuration and excellent limiting characteristics.

This type of device is well known in the past, for example in TDSH Milton: “Handbook of linear
integrated electronics for research“McGRAW
−HILL Book Company (UK) Limited,
As shown on page 318 of London (1977), a method often used is to insert a current detection resistor in series with the load and apply the voltage generated across the detection resistor between the base and emitter of the detection transistor. It's here.

However, as is well known, the knee voltage between the base and emitter of a bipolar transistor has a negative temperature coefficient of around 2mV/℃.
Moreover, if the current detection resistor is also configured on a monolithic IC chip, the resistance value of the diffused resistor in the IC generally has a positive temperature coefficient of about 2000 ppm, so the overall limiting current value will be about 5000 ppm. Has a negative temperature coefficient, e.g. limiting current value to 20℃
Even if it was set to 1A at 120℃, the value would become 0.5A, which caused many problems.

Furthermore, when a current detection resistor is inserted in series with the load, there is a problem in that power loss increases by that amount, and the utilization rate of the power supply voltage also deteriorates.

The current supply device of the present invention solves the above problems.

FIG. 1 shows a circuit connection diagram of a current supply device according to an embodiment of the present invention. In the figure, a DC motor 3, which is a load, is connected in series between the collector and emitter of a transistor 2 at both ends of a power supply 1.
A resistor 4 is connected between the base and emitter of the transistor 2, and the emitter of a transistor 5 is connected to the base. The collector of the transistor 5 is connected to the positive power supply line 1 via a resistor 6, and a bias supply circuit 7 such as a variable resistor is connected between the base of the transistor 5 and the positive power supply line 1a. There is.

On the other hand, a transistor 8 is connected to the negative power supply line 1b to which the emitter of the transistor 2 is connected.
The base of the transistor 8 is connected to the collector thereof, and a constant current source 9 is connected between the collector and the positive power supply line 1a. Furthermore, the base of the transistor 2 has an open collector output type comparator 1.
The non-inverting input terminal 10b of the comparator 10 is connected to the collector (base) of the transistor 8, and the output terminal 10c of the comparator 10 is connected to the base of the transistor 5.

Now, in the circuit of FIG. 1, it is assumed that at least transistor 2 and transistor 8 are formed on the same IC chip, transistor 2 has an emitter area 100 times that of transistor 8, and constant current source 9 If the output current is I _O and the current flowing through the DC motor 3 of the load is I _M , then when I _M > 100 I _O , the potential at the inverting input terminal 10a of the comparator 10 becomes the potential at the non-inverting input terminal 10b. , the current supplied from the bias supply circuit 7 reaches the output terminal 1 of the comparator 10.
0c, the emitter current of the transistor 2 rapidly decreases. In the end, the load current I _M depends on the output current I _O of the constant current source 9 because balance is maintained with I _M =100I _O established.

That is, by appropriately setting the output current I _O , the limit value of the load current can be set freely.

In the circuit shown in Figure 1, there is no current detection resistor connected in series with the load, so there is no increase in power loss caused by the current detection resistor or deterioration of the current/voltage utilization rate, and the temperature coefficient of the limiting current value is can be reduced to almost zero.

FIG. 2 shows another embodiment of the present invention,
In FIG. 2, a constant voltage diode 11 and a transistor 12 forming a voltage stabilizing circuit are connected between the base of the transistor 5 and the negative power supply line 1b.
The base and emitter of the transistor 12 are connected in series, and a resistor 1 is connected between the base and emitter of the transistor 12.
3 is connected.

Further, a transistor 14 is connected to the connection point between the constant voltage diode 11 and the base of the transistor 5.
The base of the transistor 14 is connected to the base of the transistor 14, and the emitter of the transistor 14 is connected to the negative power supply line 1 through a resistor 15.
The collector of the transistor 16 is connected to the base and collector of the transistor 16, and the bases of the transistors 17 and 18.

The transistors 16, 17, and 18 constitute a current mirror circuit that uses the collector current of the transistor 14 as an input current, and the transistor 17 is used as a constant current source that supplies a constant current to the transistor 8. The transistor 18 is used as a constant current source that supplies a constant current to the voltage stabilizing circuit.

Further, the collector of the transistor 12 is connected to the positive power supply line 1a via a resistor 19, the base of the transistor 20 is connected to the collector, and the emitter of the transistor 20 is connected to the negative power supply line 1b. The collector is connected to the common base of the current mirror circuit formed by the transistors 16, 17, and 18.

In the circuit shown in FIG. 2, the DC motor 3 is supplied with a constant voltage determined by the terminal voltage of the constant voltage diode 11, and the bias current value to the transistor 8 supplied by the constant current source 17 and the It has a function of preventing a current exceeding a limit current value determined by the emitter area ratio of transistor 8 and transistor 2 from flowing to the load side.

In FIG. 2, the base-emitter junction of the transistor 12 is used for the purpose of canceling out the base-emitter junction of the transistor 14 so that the terminal voltage of the voltage regulator diode 11 appears as it is across the resistor 15. However, at the same time, the transistor 12, together with the resistor 19 and the transistor 20, constitutes a starting circuit for the current mirror circuit.

That is, when the current voltage gradually increases from zero, the base current first flows through the transistor 20 via the resistor 19 to activate the current mirror circuit, and then the transistor 14 becomes conductive.

The power supply voltage increases further and voltage regulator diode 1
When current begins to flow through transistor 1, a base current also begins to flow through transistor 12, and thereafter, transistor 12 is turned on and transistor 20 is turned off.

By the way, in the embodiments of the present invention shown in FIGS. 1 and 2, a DC motor is connected as a load and a bipolar transistor is used for each transistor, but it is possible to connect a load other than the motor. is also good, and the transistor is a MOS type FET
It may be a unipolar transistor such as
In that case, the base of the bipolar transistor as the input electrode corresponds to the gate of the unipolar transistor, the collector of the bipolar transistor as the output electrode corresponds to the drain of the unipolar transistor, and the emitter of the bipolar transistor as the common electrode corresponds to the source of the unipolar transistor. corresponds.

FIG. 3 is a circuit wiring diagram showing another embodiment of the present invention constructed using enhancement type MOS transistors. In the figure, a DC motor 3 as a load is connected between the drain of an N-channel enhancement type MOS transistor 101 and a positive power supply line 1a, and a frequency generator (FG) 103 connected to the DC motor 3 is connected The output is applied to the rotational speed control circuit 107, and the output of the rotational speed control circuit 107 is applied to the N-channel enhancement type MOS transistor 101.
is applied to the gate of

On the other hand, a drain current is supplied by a constant current source 109 to an N-channel enhancement type MOS transistor 108 whose source is connected to the negative side power supply line and whose gate is connected to the drain. The non-inverting input terminal 110b of the comparator 110 is connected to the non-inverting input terminal 110b of the N-channel enhancement type MOS transistor 101. connected to the gate.

Note that the N-channel enhancement type
A resistor 104 is connected between the gate and source of the MOS transistor 101.

In FIG. 3, a rotation speed control circuit 107 is a circuit for constant speed control of the rotation speed of the DC motor 3 to a predetermined value based on information from the frequency generator 103. N-channel enhancement type MOS transistor 1 depending on the magnitude of the load connected to the rotating shaft of
It has a function of generating a gate bias voltage to adjust the amount of current flowing through the gate.

The control operation of the output current in the circuit of FIG. 3 is the same as that of the circuit of FIG. 1, so a description thereof will be omitted here.

As described above, the current supply device of the present invention has an output electrode (in a bipolar transistor, a collector,
Drain in a MOS transistor. ) and a common electrode (the emitter for bipolar transistors and the source for MOS transistors) are connected to one end of the load and the other to one end of the power supply (implementation of Figures 1 and 2). In the example, transistor 2 corresponds to
In the illustrated embodiment, the MOS transistor 101
is applicable. ), a common electrode is connected to the common electrode of the first transistor, an input electrode (base in a bipolar transistor, gate in a MOS transistor) is connected to an output electrode, and a predetermined amount of current is applied to the output electrode. is supplied to the second transistor (transistor 8 in the embodiments shown in FIGS. 1 and 2), and the third
In the illustrated embodiment, MOS transistor 108
is applicable. ), and current supply means for supplying current to the output electrode of the second transistor (constant current source 9 in the embodiment of FIG. 1, transistor 17 in the embodiment of FIG. 2, and current supply means for supplying current to the output electrode of the second transistor); , the constant current source 109 corresponds to each case), and
Comparison means for comparing the potential of the input electrode of the first transistor and the potential of the input electrode of the second transistor (corresponding to the comparator 10 in the embodiments of FIGS. 1 and 2, and the comparator 10 in the embodiments of FIG. 3) In the example, this corresponds to a comparator 110), and an output that supplies an output current or an output voltage to the input electrode of the first transistor, the output current or the output voltage including at least a current value or a voltage value depending on the comparison output signal from the comparison means. Stage driving means (in the embodiments shown in FIGS. 1 and 2, the output stage driving means is constituted by the bias supply circuit 7 and the transistor 5, and in the embodiment shown in FIG. and a composite connection of the output signals of the comparator 110 constitutes an output stage driving means. This feature allows the load current to be detected without connecting a resistive element in series with the load, so the power supply voltage utilization efficiency does not deteriorate and it provides excellent control over changes in ambient temperature. It has great effects, such as realizing special characteristics.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are all circuit diagrams of current supply devices according to embodiments of the present invention. 1...Current, 2,8,17...Transistor,
3...DC motor (load), 7...Bias supply circuit, 9,109...constant current source, 10,110...
... Comparator, 101, 108 ... N-channel enhancement MOS transistor, 10
7...Rotation speed control circuit.

Claims (1)

[Claims] 1 A first transistor in which one of an output electrode and a common electrode is connected to one end of a load and the other is connected to one end of a power supply, a common electrode is connected to a common electrode of the first transistor, and an input electrode is connected to an output electrode. a second transistor connected to the output electrode of the second transistor and having a predetermined amount of current supplied to its output electrode; current supply means for supplying current to the output electrode of the second transistor; and an input electrode of the first transistor. comparing means for comparing the electric potential with the electric potential of the input electrode of the second transistor;
an output stage drive means for supplying the current to the input electrode of the first transistor, and is configured to supply current to the load from the output electrode of the first transistor or the common electrode.