JPH0542487Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a constant current circuit whose output current can be switched.

(Conventional technology) Conventional technology in this field includes "Dynamic Ham Series 1 Power Supply Design and Production" by Kazuaki Nishida and Isao Yano, QC Publishing, page 27.
A resistor R _i connected in series to detect the emitter current of the transistor as described in ~29
, a plurality of diodes connected between the base of the transistor and the other end of the resistor, and a resistor connected to 0V from the base of the transistor,
The voltage V _D generated across the plurality of diodes becomes a constant value, and the output current becomes a constant current determined by = (V _D - V _BE )/R _i from the base-emitter voltage V _BE of the transistor.

(Problem that the invention attempts to solve) Conventionally, when switching the output current and using it,
The resistance R _i was switched using a relay, a semiconductor switch, or the like. However, when using this constant current circuit to charge a storage battery or as an electronic load for a power supply, it is necessary to switch a current of around several amperes, and the relays and semiconductor switches used for switching must be large and expensive. There was a drawback that it required

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a constant current circuit with a transistor that controls the output current.
a resistor having one end connected to the emitter of the transistor; a plurality of diodes connected in series between the base of the transistor and the other end of the resistor; and a plurality of diodes connected to the base of the transistor and receiving an external voltage; The device includes means for controlling the current flowing through the plurality of diodes, and means for substantially short-circuiting some of the plurality of diodes in response to the external voltage.

(Function) According to the present invention, instead of using a large and expensive relay or semiconductor switch to switch the resistor connected in series with the emitter of the output transistor, the diode connected to the base of the output transistor is switched. Focusing on the fact that the voltage V _D at both ends changes depending on the current flowing through the diode, and the number of diodes connected in series,
The current flowing through the diode and the number of diodes are switched using a small and inexpensive semiconductor switch.
The emitter current of the output transistor, in other words, the output current can be switched.

(Example) FIG. 1 is a block diagram of an application example of a conventional constant current circuit, in which the + and - outputs of a DC power supply 1 are connected to +IN and -IN of a constant current circuit 2, respectively.
+OUT and -OUT of constant current circuit 2 are +OUT and -OUT of load 3.
IN and -IN, and a control voltage generator 4 is connected to the control terminal CONT and -OUT output of the constant current circuit 2.

Next, the configuration of the constant current circuit 2 will be explained.

+ input of constant current circuit 2 is current detection resistor R1
and to the bases of the transistors via diodes D1 to D3, respectively. The collector of transistor Q1 is connected to +OUT of constant current circuit 2. The base of transistor Q1 is connected to diode D.
It is connected to the collector of transistor Q2 for current variable control of No. 1 to No. 3. The emitter of transistor Q2 is connected to - of constant current circuit 2 via resistor R2.
-IN of constant current circuit 2 and -
OUT is connected. The base of the transistor Q2 is connected to a control terminal CONT, and a control voltage generator 4 that generates a control voltage V _C is connected between the control terminal CONT and -OUT of the constant current circuit 2.

FIG. 2 is a diagram showing an example of current-forward voltage characteristics of a diode.

The operation of the constant current circuit 2 will be described below with reference to FIGS. 1 and 2.

When the control voltage V _C is input to the control terminal CONT, the transistor Q2 is activated and causes current to flow through the resistor R2. At this time, the emitter current _e2 of the transistor Q2 flowing through the resistor R2 is a constant expressed by _e2 = (V _C - V _BE2 )/R2 (Equation 1), where the voltage between the base and emitter of the transistor Q2 is V _BE2 . It becomes an electric current. Furthermore, the emitter current
_e2 is the sum of base current _B1 of transistor Q1, _D flowing through diodes D1 to D3, and base current _B2 of transistor Q2, but base current _B2 is the DC current amplification factor of collector current _C2.
Since it is 1/h _fe2 (usually 100 to 500) (in other words, the base current _B2 is sufficiently smaller than the collector current _C2 ), _C2 + _B1 + _D = (V _C − V _BE2 )/R2
...(Formula 2)

The emitter current _e1 of the transistor Q1 is expressed as _e1 = (V _D - V _Be1 )/R1 (Formula 3), where the base-emitter voltage of the transistor Q1 is V _Be1 and the forward voltage of the diodes D1 to D3 is V _D. The constant current is expressed as . Furthermore, the emitter current
_e1 is the sum of the collector current _C1 of the transistor Q1 (in other words, the output current) and the base current _B1 of the transistor Q1, and the base current _B1
is the DC current amplification factor h _fe1 of the collector current _C1 (usually,
75 to 250) (in other words, because the base current _B1 is sufficiently smaller than the collector current _C1 ), the collector current _C1 and the emitter current _e1 become substantially equal.

When the current (35 mA) shown at point B in FIG. 2 is passed through the diodes D1-3, 2.4V is generated across the diodes D1-3. Output current _C at this time
Assuming that V _BE1 = 0.8V, a current of _C = (2.4-0.8)/R1 = 1.6/R1 (Equation 5) is obtained. Here, change the current (200mA) shown from point B to point C in Figure 2 and connect diode D1.
~3, both ends of diodes D1~3 have
3.6V is generated. At this time, the output current _C is calculated by assuming that _{V BE1} = 0.8V for convenience since the base-emitter voltage changes only slightly. can get.

The change in output current between point B and point C in Figure 2 is expressed by formula 5
and 5', 1.75 times the output current can be obtained. Therefore, the output current can be changed more than twice between point A and point C in the second diagram.

Here, a constant current circuit is used as a circuit for driving the current flowing through the diodes D1 to D3.
If the load fluctuation characteristics and ripples of the DC power supply 1 are small, the current may be changed by switching the resistance. However, when using the DC power supply 1 with large load fluctuations and ripples, the diodes D1 to
It is preferable to use a constant current circuit for the drive circuit of D3.

FIG. 3 is a block diagram of an example of a simulated load device suitable for aging while changing the load of a DC power supply, or a constant current circuit used when performing a discharge characteristic test similar to that during actual operation of a storage battery.

FIG. 4 is a timing chart when the simulated load device is activated.

Hereinafter, the configuration of the constant current circuit 2a shown in FIG. 3, which uses a resistor and a constant voltage diode in place of the control voltage generator 4 shown in the block diagram shown in FIG. 1, will be explained. However, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The base of a transistor Q2 is connected to +IN of the constant current circuit 2a in FIG. 3 via a current limiting resistor R3. -IN of constant current circuit 2a has
The collector of transistor Q1 is connected to the base of transistor Q2 via constant voltage diode ZD1.
The base of the transistor Q2 is connected through a diode D4 and a transistor Q3 serving as an analog switch, and the base of the transistor Q3 is connected through a resistor R5. The control terminal CONT of the constant current circuit 2a is connected to the base of a transistor Q3 via a resistor R4.
Control terminal CONT and - of constant current circuit 2a
An oscillator 5 for switching the control cycle is connected between OUT and OUT.

The operation of the constant current circuit 2a shown in FIG. 3 will be explained below.

When a voltage is applied from the DC power supply 1 to the constant current circuit 2a, a constant current I _C determined by the diodes D1 to D3 and the resistor R1 flows through the transistor Q1. The constant current I _C is the current I _D flowing through the diodes D1 to D3.
It is determined by the voltage V _D generated by The current _ID is
It is switched by the base voltage of transistor Q2.

In the constant current circuit 2a, the base voltage of the transistor Q2 is controlled by the voltage generated in the constant voltage diode ZD1 or diode D4 when a current flows from the DC power supply 1 to the constant voltage diode ZD1 or the diode D4 via the resistor R3. Ru.

The output of the oscillator 5 (in other words, the constant voltage circuit 2a
The control terminal CONT) is switched periodically as shown in FIG. 4a.

When the output of the oscillator 5 is at H level, the transistor Q3 becomes conductive, and the diode D is connected from the DC power supply 1 through the resistor R3 and the transistor Q3.
4, the base voltage of the transistor Q2 becomes the voltage (V _D4 +V _CE3 ) which is the sum of the voltage V _D4 generated in the diode D4 and the collector-emitter voltage V _CE3 of the transistor Q3, has a current I _D as shown in Figure 4b.
(= about 10 mA) flows, and the constant current I _C flows about 1.5 A as shown in Figure 4c.

Furthermore, when the output of the oscillator 5 is at L level, the transistor Q3 is cut off, current flows from the DC power supply 1 to the voltage regulator diode ZD1 via the resistor R3, and the base voltage of the transistor Q2 is generated in the voltage regulator diode ZD1. The voltage becomes V _ZD1 , a current I _D (=200mA) as shown in Fig. 4b flows through the diodes D1 to D3, and the constant current I _C flows as shown in Fig. 4c.
As shown in the figure, a current of about 2.7A flows. still,
The voltage V _ZD1 of the constant voltage diode ZD1 is determined by the voltage V _D4 of the diode D4 and the collector-emitter voltage V _CE3 of the transistor Q3, assuming that the base current I _B1 of the transistor Q1 changes little (I _D > I _{B1 )} . This is approximately 20 times the added voltage (V _D4 + V _CE3 ).

FIG. 5 is a block diagram of an embodiment of a charging circuit to which the constant current circuit of the present invention is applied. Figure 6 shows
This is a time chart showing the characteristics of charging voltage and charging current of a storage battery.

In FIG. 5, 2b is a constant current circuit, 6 is a storage battery such as a nickel-cadmium storage battery or a small sealed lead-acid battery, and 7 is a voltage detector having a hysteresis width for detecting the charging voltage _VBT of the storage battery 6. Components that are the same as those in the block diagram shown in FIG. 3 are designated by the same reference numerals, and their description will be omitted.

A storage battery 6 is connected between +OUT and -OUT of the constant current circuit 2b, a voltage detector 7 is connected in parallel with the storage battery 6, and the voltage _VBT of the storage battery 6 is set to a predetermined voltage (the internal temperature of the storage battery at the end of charging). (voltage rise accompanying the rise) is detected and inputted to the control terminal CONT of the constant current circuit 2b.

The constant current circuit 2b of this embodiment adds transistors Q4 and Q5 for shorting the diodes D1 and D2 to the constant current circuit 2a of _FIG . It is becoming possible.

A transistor Q4 is connected in parallel to the diodes D1 and D2, and the base of the transistor Q4 is
A bias resistor R6 is connected between the collectors. The base of the transistor Q4 is connected to -IN of the constant current circuit 2b via the transistor Q5. A resistor R8 is connected between the base and emitter of the transistor Q5, and the base of the transistor Q5 is connected to the base of the transistor Q3 via a current limiting resistor R7.

The operation will be described below with reference to FIGS. 5 and 6.

At the beginning of charging the storage battery 6, the charging voltage _VBT of the storage battery 6 has not reached the predetermined voltage, so the output of the voltage detector 7 is at H level. Therefore, transistors Q3 and Q5 become conductive, transistor Q4 becomes cut off, and diode D1
~D3 has the current shown at point B in Figure 2 (approximately
35 mA) flows, and the voltage V _D across the diodes D1 to D3 becomes 2.4V. Therefore, the charging current I _C of the storage battery 6 is I _C = (I _D - V _BE1 )/R1 when the base-emitter voltage V _BE1 of the transistor Q1 is 0.8V.
It is charged as shown in Figure 6b with a current of = 1.6/R1 = 0.2C. Then, about 8 hours after starting the 0.2C charging, the voltage V _BT rises as the internal temperature of the storage battery 6 rises, and becomes higher than the predetermined voltage of the voltage detector 7 (point E in Figure 6 a). ), the output of the voltage detector 7 becomes L level, and the transistor Q
3 and Q5 are cut off, and transistor Q4
becomes conductive, and diodes D1 and D2 are shorted by transistor Q4. At this time, a current (200 mA) shown at point C in FIG. 2 flows through the diode D3, and the voltage across the diode D3 becomes 1.2V. Therefore, the charging current I _C of the storage battery 6
is 0.8V assuming that the base-emitter voltage V _BE1 of the transistor Q1 is not affected by the emitter current, and the current is I _C = (V _D - V _BE1 )/R1 = 0.4/R1 = 0.05C. It will be charged.

(Effects of the invention) As explained in detail above, according to the invention, the current and setting resistor connected in series with the emitter of the output transistor can be switched using large and expensive relays, semiconductor switches, etc. By switching the number of diodes connected between the base of the transistor and the other end of the current setting resistor, the voltage across the diodes is set to a predetermined value, and the output current is switched. Therefore, it is possible to provide a small and economical constant current circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an application example of a conventional constant current circuit, and FIG. 2 is a diagram showing an example of current-forward voltage characteristics of a diode. Figure 3 is a block diagram of an example of a simulated load device using a constant current circuit.
The figure is a timing chart when the simulated load device is activated. FIG. 5 is a block diagram of an embodiment of a charging circuit to which the constant current circuit of the present invention is applied, and FIG. 6 is a time chart showing characteristics of charging voltage and charging current of a storage battery. 1...DC power supply, 2, 2a, 2b...constant current circuit, 3...load, 4...control voltage generator, Q1,
Q2...transistor, D1, D2, D3...diode, R1, R2...resistance.

Claims (1)

[Claims for Utility Model Registration] A transistor for controlling output current, a resistor having one end connected to the emitter of the transistor, and a plurality of diodes connected in series between the base of the transistor and the other end of the resistor. and means connected to the base of the transistor and receiving an external voltage to control the current flowing through the plurality of diodes; and means receiving the external voltage and substantially short-circuiting a portion of the plurality of diodes. A constant current circuit comprising: