JPS5922967B2 - constant current circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a constant current circuit with a relatively simple configuration and low voltage loss.

FIG. 1 shows a simple constant current circuit that has been widely used in the past.One feed line 1 is connected to the collector of a leg restraining transistor 2.
The emitter of is connected to the other feed line 4 via a detection resistor 3, and a detection transistor 5 is connected to both ends of the detection resistor 3.
The collector of the detection transistor 5 is connected to the base of the control transistor 2 and is also connected to the feed line 1 via a resistor 6.

Further, the feed line 1 is connected to the feed terminal 1a, the feed line 4 is connected to the feed terminal 4a, and the feed line 4 is connected to the feed terminal 1a, and the feed line 4 is connected to the feed terminal 4a.
A and a load resistor 8 are connected between the power supply terminal 4a and the power supply terminal 4a.
are connected in series.

Incidentally, a capacitor 9 for preventing oscillation is connected in parallel with the detection resistor 3. Now, in the constant current circuit shown in FIG. 1, the output current 10 is controlled so that the voltage across the detection resistor 3 is equal to the base-emitter forward voltage EBE5 of the detection transistor 5. , the current voltage is EI
, where the resistance value is RA and the resistance value of load resistor 8 is RL, E
When 1>10(RA+RL), the output current 10 is as follows.

10=(1) In other words, when the output current 10 changes due to changes in the load, the voltage across the detection resistor 3 also changes, and the collector current of the detection transistor 5 changes rapidly. The voltage between the emitter of the cooling transistor 2 and the feed line 4, that is, the voltage across the detection resistor 3, is returned to its original value, and the output current is 1.

stability is maintained. Now, Figure 2 shows the circuit shown in Figure 1, with the resistance value RA of resistor 3 being 180Ω, and the resistance value RB of resistor 6 being 180Ω.
0KΩ, the resistance RL of the load resistance 8 is 820Ω, the transistors 2 and 5 are silicon NPN transistors 2SC-828 (manufactured by Matsushita Electric), and the capacitance of the capacitor 9 is 1 μF. Output current 1 for changes in power supply voltage EI .

This shows the changes in (Actual Measured Value) From Fig. 2, in the circuit of Fig. 1, when the power supply voltage EI becomes 5V or more, the output current is 1.

is almost stabilized, and when the lowest power supply voltage is 5, the output current is 3.68 mA, and when the power supply voltage is 20, the output current is 4.16 mA. By the way, the characteristic shown by the broken line in Figure 2 is when the resistance value RA of the detection resistor is 1.
80Ω, the resistance value RL of the load resistor is 820Ω, and the output current is 4mA.This is the output current special characteristic for the power supply voltage of an ideal constant current circuit.In this case, the output current is detected from the lowest power supply voltage. While the value obtained by subtracting the voltage drop at the resistor and load resistor is the value, the actual characteristics of the constant current circuit shown in Figure 1 are the output voltage from the power supply voltage when the output current is 3.68 mA. The value obtained by subtracting the voltage drop across the detection resistor and load resistor due to current is 1.32. This causes a combined voltage drop of 3.68V across the sense resistor and load resistor, for example.

In other words, in order to obtain a stabilized output current of 3.68 mA, a power supply voltage of 5 V or more is required. This is a big problem for portable devices. In the circuit shown in Figure 1, the value obtained by subtracting the voltage drop at the detection resistor and load resistor due to the output current from the minimum power supply voltage is large because the emitter potential of the cape transistor 2 is lower than the potential of the feed line 1 at the base of the same transistor.・This is due to the fact that the voltage does not increase beyond the value obtained by subtracting the forward voltage between the emitters.To eliminate this inconvenience, connect the other end of the resistor 6, one end of which is connected to the base of the leg restraining transistor 2, to the power supply line. It is sufficient to connect it to a power supply point with a potential higher than 1, but in this case, an additional power supply is required, which causes many problems.

The constant current circuit of the present invention solves the above problems.

FIG. 3 shows a circuit connection diagram of a constant current circuit according to an embodiment of the present invention, and the same parts or parts as in FIG. 1 are indicated by the same figure numbers, and the explanation thereof will be omitted.

As shown in FIG.
The emitter of the cape transistor 10 is connected to the feed line 4 via the detection resistor 3, and the collector of the cape cape transistor 10 is connected to the feed line 4, and a detection transistor 1 complementary to the cape transistor 10 is connected to the emitter of the cape transistor 10.
The base and emitter of the detection transistor 12 are connected to both ends of the detection resistor 3, and the collector of the detection transistor 12 is connected to the base of an amplification transistor 13 complementary to the control transistor 10, and connected to the feed line 1 via a resistor 14. The emitter of the amplifying transistor 13 is connected to the feed line 4 via a resistor 15, and the collector thereof is connected to the base of the suppressing transistor 10 and to the feed line 1 via a resistor 16. There is.

Now, in the constant current circuit shown in FIG. 3, if the forward voltage between the base and emitter of the detection transistor 12 is EBE2, and the condition EI>IO (RA+RL) is satisfied, the output current is 1.

is the same as in the case of Fig. 1, that is, the output current is 1 due to load fluctuations, etc.

When the current changes, the collector current of the detection transistor 12 changes rapidly, and the collector current of the amplification transistor 13 also changes rapidly.
0 base current and collector current change to output current 1.
is controlled so that it returns to its original value. In the circuit shown in FIG. 3, when EI<IO(RA+RL), no base current flows through the detection transistor 12, and the collector current also becomes negative, so that the amplification transistor 13 is completely saturated.

Since the suppression transistor 10 is also completely saturated when the amplification transistor 13 is completely saturated, the voltage loss between the collector and emitter of the suppression transistor 10 is considerably reduced. By the way, Figure 4 shows the circuit shown in Figure 3, with the resistance value RA of resistor 3 being 180Ω, the resistance value Rc of resistor 11 being 1KΩ, the resistance value RD of resistor 14 being 10KΩ, the resistance value RE of resistor 15 being 1KΩ, and the resistance value of resistor 16 being 1KΩ. The resistance value RF of
0KΩ, resistance value RL of load resistor 8 is 820Ω, capacitance of capacitor 9 is 1μF, transistor 10 is silicon PN.
This graph shows the change in output current 10 with respect to the change in power supply voltage EI when P-type transistor 2SA-564 (manufactured by Matsushita Electric) and transistors 12 and 13 are silicon NPN transistors 2SC-828 (manufactured by Matsushita Electric). It is.

(Actual measurement value) From Figure 4, in the constant current circuit shown in Figure 3, the output current is 4.10 mA when the lowest power supply voltage is 4.2V, and the detection resistance and load resistance depending on the output current from the lowest power supply voltage. It can be seen that the value obtained by subtracting the voltage drop at is 0.1V, which is extremely small compared to the circuit shown in FIG.

Although FIG. 3 shows an example in which the constant current circuit of the present invention is constructed using bipolar transistors, it can also be constructed using field effect transistors as shown in FIG.

In the constant current circuit of FIG. 5, a P-channel enhancement type MOS transistor 17 is used as a control transistor, an N-channel enhancement type MOS transistor 18 is used as a detection transistor, and an N-channel enhancement type MOS transistor 19 is used as an amplification transistor. , resistor 11 and resistor 15 in FIG. 3 have been omitted.

It is also possible to mix bipolar transistors and field effect transistors for the suppression transistor, detection transistor, and amplification transistor. In this case, the detection transistor and the amplification transistor may each be complementary transistors with respect to the bias voltage of the suppression transistor.

That is, in the constant current circuit of the present invention, the common electrode of the braking transistor is connected to one feed line, the output electrode of the braking transistor is connected to the other feeding line via a detection resistor, and the common electrode of the braking transistor is connected to the other feeding line via a detection resistor. and an input electrode and a common electrode of a detection transistor complementary to the bias voltage are connected to both ends of the detection resistor, and an output electrode of the detection transistor is connected to an input electrode of an amplification transistor complementary to the cape transistor and the bias voltage. and a common electrode of the amplification transistor is connected to the other feed line,
The output electrode is connected to the input electrode of the cape transistor, and in the case of a bipolar transistor, the common electrode is the emitter, the output electrode is the collector, and the input electrode is the base. In this case, the common electrode becomes a source, the output electrode becomes a drain, and the input electrode becomes a gate. Note that the detection transistor, the amplification transistor, and the suppression transistor do not need to be a single transistor, but may be transistors connected in a composite manner, and especially when obtaining a large current output, the suppression transistor is connected in a Darlington manner.

As described above, in the constant current circuit of the present invention, the output electrode of the detection transistor, in which the input electrode and the common electrode are connected to both ends of the detection resistor, is connected to the input electrode of the amplification transistor, and the output electrode of the amplification transistor is connected to the input electrode of the amplification transistor. , is connected to the input electrode of a cape transistor of a complementary type with respect to the bias voltage of the detection transistor and the amplification transistor, and the output electrode of the cape transistor is connected to the detection resistor, so that the control at the lowest power supply voltage is possible. It is possible to obtain a constant current circuit with low loss voltage in the leg transistors, which is very effective.

[Brief explanation of the drawing]

Fig. 1 is a circuit wiring diagram showing a conventional example, Fig. 2 is a characteristic diagram for explaining its operation, and Fig. 3 is a circuit wiring diagram of a constant current circuit in an embodiment of the present invention. , 4th
This figure is a characteristic diagram for explaining the operation of the circuit of FIG. 3, and FIG. 5 is a circuit connection diagram of a constant current circuit in another embodiment of the present invention. 1, 4...Feeding line, 3...Detection resistor, 10...Control cape transistor, 12...
・Detection transistor, 13... Amplification transistor, 17... Control cape transistor, 18...
...Detection transistor, 19...Amplification transistor, 10-13...Bipolar transistor, 17-19...Field effect transistor.

Claims (1)

[Claims] 1. A common electrode of a control transistor is connected to one feed line, an output electrode of the control transistor is connected to the other feed line via a detection resistor, and the bias voltage is complementary to that of the control transistor. An input electrode and a common electrode of a detection transistor are connected to both ends of the detection resistor, an output electrode of the detection transistor is connected to an input electrode of an amplification transistor complementary to the control transistor in terms of bias voltage, and a common electrode of the amplification transistor is connected to both ends of the detection resistor. The electrode is connected to the other feed line, the output electrode is connected to the input electrode of the control transistor, and a second resistor is connected between the output electrode of the detection transistor and one of the feed lines, and the amplification A constant current circuit characterized in that a third resistor is connected between the output electrode of the transistor and one power supply line. 2. The detection transistor, the amplification transistor, and the control transistor are each constituted by a bipolar transistor, and the input electrode, output electrode, and common electrode are the base, collector, and emitter of the bipolar transistor, respectively. Constant current circuit according to range 1. 3. The detection transistor, the amplification transistor, and the control transistor are each constituted by a field effect transistor, and the input electrode, output electrode, and common electrode are the gate, drain, and source of the field effect transistor, respectively. Constant current circuit according to range 1.