JPH0343809A - Temperature compensating circuit and printer with this circuit - Google Patents

Abstract

PURPOSE:To easily obtain the output voltage undergone the temperature compen sation by using the control voltage as a parameter to control the output charac teristic of a voltage conversion means to the temperature. CONSTITUTION:A 1st constant current source 16 has its current value controlled by the control voltage, and a 2nd constant current source 23 has its fixed current value. A 1st current synthesization means 25 is added to synthesize the outputs of both current sources 16 and 23, together with a 3rd constant current source 26 having its current value dependent on the temperature change, a 2nd current synthesization means 28 which synthesizes the outputs of the means 25 and the source 26, and a voltage conversion means 29 which applies the voltage conversion to the output of the means 28. The output characteristic of the means 29 is controlled by the control voltage to the temperature. As a result, the output characteristic of the means 29 can be controlled to the temperature with the control voltage used as a parameter. Thus it is possible to easily obtain the output of the means 29 undergone the temperature compensa tion.

Description

Detailed Description of the Invention Kui> Industrial Application Field The present invention relates to a temperature compensation circuit and a printing device (L) equipped with the same.
(ED printers, thermal printers, etc.).

(0) Prior Art As an LED driver array for an LED printer, for example, Japanese Patent Application No. 63-292882 has been proposed. FIG. 2 is a drawing showing the above-mentioned technique, and specifically shows a 64-bit LED driver array, which will be explained below. In FIG. 2, (1) is a 64-bit shift register that shifts data input from a serial input in synchronization with a clock, and (2) is a serial data output circuit. Also, (3) is a 64-bit shift register (
(1) is a 64-bit latch circuit that latches the parallel data; (4) is a strobe circuit that synchronizes the 64-bit parallel data with a strobe signal and inputs it to the switch input of the next stage switch circuit (5). (5) ) is a switch circuit that controls on/off the 64 output transistors in the current output circuit <6) according to the contents of 64 parallel data. (6> is a current output circuit, which outputs a load drive current according to the output voltage of the current control circuit (11). (7> is an LED as a load, which emits light when a drive current is supplied. 8> is a voltage conversion circuit that detects the amount of current output from the current output circuit (6) and converts it into a voltage, and (9) is a reference voltage generation circuit (1).
A differential amplifier (11) inputs the reference voltage Vref inputted through the differential amplifier (8) to the positive input and inputs the output voltage of the voltage conversion circuit (8) to the negative input. This is a current control circuit that controls the amount of output current of the current output circuit (6) in accordance with the output voltage value.In other words, the switch circuit (5)
), current output circuit (6).

Since the differential amplifier (9>) and the current control circuit (11) constitute a negative feedback loop, the negative feedback loop operates so that the reference voltage V ref and the output of the voltage conversion circuit (8) match. From this, the reference voltage ■re is applied to the LED (7).
A constant drive current based on f will flow. In this way, printing is performed on the paper using the luminance of the light emitted from LED (7).

Here, L E D (7) has a characteristic that the luminance of light emission decreases as the ambient temperature of the circuit increases, and the reference voltage Vref remains constant even if the ambient temperature of the circuit changes. Therefore, while the LED printer is running, the LED
If the ambient temperature of the driver array circuit increases, the L
Although it is necessary to increase the driving current of the ED (7), since the reference voltage V ref is constant without temperature compensation, the luminance of the LED (7) decreases, causing a change in print density. There was a problem that this occurred.

Therefore, a circuit for temperature compensating the reference voltage V ref is required, for example 'Nationalτechn
icalReport Vol, 29 No. 3 J
A temperature compensation circuit is presented on page 401 of Un, 1983J. FIG. 3 is a circuit diagram showing a temperature compensation circuit for the exhaust gas. In FIG. 3, (12) is a transistor Q,
and transistor Q.

This is a current mirror circuit consisting of. (S) is a current mirror circuit consisting of transistors Q and Q, and the emitter area ratio of these transistors QttQ is set to 1:N. and the collector-emitter path of the diode-connected transistor Q3, and the collector-emitter path of the transistor Q3.
The emitter path and a resistor (14) with a resistance value RI are connected in series between the power supply voltage . A collector-emitter path is also connected in series between the power supply voltage VCC and ground.

and the collector-emitter path of the transistor Q constituting the current mirror circuit and the resistor (15) with a resistance value R2,
It is connected in series between the power supply voltage VCC and ground. By injecting a control current Ia into the connection point A between the emitter of the transistor Q and the resistor (14), the control current Ia is injected into the collector of the transistor Q6 and the resistor (14).
5), the output voltage V is obtained from the connection point B.

Here, if the current flowing in the series path of transistors Q, , Q is I+, the current flowing in the series path of transistors Q, , Q is 3, and the current flowing in transistor Q6 is Is, then L −l5ex p (qVsi+/k'r)
...-= (1) Is-NIsexp(qVm*
*/ k engineering) ・-・----(2) However, Is: Saturation current of transistor Q, Vmmt F Vllll: Transistor Ql, Ql
(7) Base-emitter forward voltage q: Charge: Bormann constant T: Absolute temperature. And the current 1 shown in equations (1) and (2). ,I,
Since they are equal, Vsi+V, , -kT1ogN/Q"
``''''''(3) The current flow is I! considering the control current Ia. −(Vlll−Vllll)/RI Ia=
kT 1ogN/R,q -Ia...
.=...(4), and since I,-1, the output voltage V, is V,=1. R.

”= R*k1ogN/R+qRtIa”
・"(5).As is clear from equation (5), the output voltage V has a constant temperature gradient in proportion to the absolute temperature T. This situation is shown in Figure 4. This is a characteristic diagram of absolute temperature T and output voltage V, and this characteristic diagram uses control current Ia as a parameter.In other words, if the solid line characteristic is obtained when control current 1g is a predetermined value, control current Ia is If the control current Ia is made larger than the predetermined value, the characteristics shown by the dashed line will be obtained, and if the control current Ia is made smaller than the predetermined value, the characteristics shown by the broken line will be obtained.

If the output voltage V having such a temperature gradient is used as the reference voltage V ref in FIG. 7) The luminance of the light emitted by the printer is kept constant, thereby preventing variations in print density.

(c) Problems to be Solved by the Invention However, in the conventional technique, when the output voltage V in FIG. 3 is used as the reference voltage V ref in FIG. 2, a circuit for temperature compensating the control current 1a is also required. It becomes necessary. Therefore, the structure of this temperature compensation circuit becomes complicated, and especially when the circuits of FIGS. 2 and 3130 are integrated into an IC, there are problems such as an increase in the size of the chip and an increase in cost. Therefore, the present invention focuses on absolute temperature T and output voltage ■. It is an object of the present invention to provide a temperature compensation circuit which has a simple configuration and is suitable for IC implementation, by controlling the characteristics of the temperature compensation circuit using a control voltage.

(d) Means for Solving the Problems The present invention has been made to solve the above problems, and includes a first constant current source whose current amount is controlled based on a control voltage, and a first constant current source whose current amount is controlled based on a control voltage. a fixed second constant current source; a first current synthesizing means for synthesizing the outputs of the first constant current source and the second constant current source; and a third current synthesizing means whose current amount depends on temperature changes. a constant current source, a second current combining means for combining the outputs of the first current combining means and the third constant current source, and a voltage converter for converting the output of the second current combining means into a voltage. means, and the output characteristic of the voltage conversion means with respect to temperature is controlled by the control voltage.

(*> Effect) According to the present invention, since the output characteristics of the voltage conversion means with respect to temperature can be controlled using the control voltage as a parameter, it is possible to easily obtain a temperature-compensated output of the voltage conversion means, and it is possible to reduce costs. Furthermore, when the circuit of the present invention is integrated into an IC, the area occupied by the chip can be suppressed to a small extent, contributing to the miniaturization of the chip, and the degree of integration of the IC can be further improved.

(to) Examples The details of the present invention will be specifically explained with reference to the illustrated embodiments.

In FIG. 1, (16) is the first constant current source, which is the transistor Q*+Q+* that constitutes the current mirror circuit.
and control transistor Q, whose resistance values are Rg and R@, respectively.
, R, and resistors (17), (18), and (19). and the resistor (18>) and the transistor Q.

Q, and the series path of the resistor (17) is tR voltage Vc.

and ground. (20) is a stabilizing regulator for stabilizing the source voltage vcc. (21) is an operational amplifier, and a variable power supply (
22) is connected, and its negative (-) terminal is connected to the connection point between the transistor Q and the resistor (17>).In other words, the operational amplifier (21) Base-emitter forward voltage vI1
1. ．． This is to prevent dependence on the control voltage VCOII and the current I8, and to improve the linearity of the control voltage VCOII and the current I8.

(23) is a second constant current source, which is composed of a transistor Q lj * Q 14 forming a current mirror circuit and a resistor (24) having a resistance value R4. The series path between the transistor Q0 and the resistor (24) is connected to the power supply voltage V
Connected between CC and ground.

(25) is a first current combining means, which is composed of transistors Q+t+Q+t forming a current mirror circuit.

and a series path of the transistors Q III Qll;
and the series circuits of the transistors Qts, Q, , are connected between the power supply voltage VCC and the ground, respectively. That is, the first current combining means (25>) combines the currents obtained from the first constant current source (16) and the second constant current source (23).Specifically, , the current flowing through the collector of the transistor QI3 is I., then the transistor Q.

Since transistors Q11 constitute a current mirror circuit, the transistors Q1. For collectors? [IlA will flow, and electricity iI will flow at point A. O and I are combined and the combined current is l. It becomes O-L.

(26) is a third constant current source that outputs a current proportional to temperature, has an emitter area ratio of N, and forms a current mirror circuit with transistors Q, , Q, which form a current mirror circuit. transistors Q, ,Q, and a transistor Q that constitutes a current mirror circuit with the transistor Q.

and a resistor (27〉) with a resistance value R1.The series path of the transistors Q, , Q and the resistor (27〉) and the series path of the transistors Q, , Q are connected to the power supply voltage vCc and the ground, respectively. is connected between.

28) is a second current combining means, which is composed of transistors Q, . The collector-emitter path of the transistor Q is the transistor QI! The transistor Qs is connected in parallel with the collector-emitter path of the transistor Qs.

The series path of Q is the power supply voltage V. It is connected between C and ground. In other words, the second current combining means (28)
The combined current obtained from the first current combining means (25) and the current obtained from the third constant current source (26) are combined. Specifically, the current flowing through the collector of the transistor Q is I. ? Then, since the transistors Q, , Q constitute a current mirror circuit, the transistor Q.

There is a current I in the collector of. OIX will flow, and B
Current I at the point. 1. Io. -■8 is synthesized and becomes I.

? -(I..-■ becomes.

29) is a voltage converting means, which consists of a resistor (3
0) (31). And these resistances (30) (3
Since the connection point 1) is point B connected to the collector of the transistor Q, the combined current l. -r-(■.

. -1,) will be converted into voltage. The output voltage V thus obtained through voltage conversion is used as the reference voltage V ref in FIG. 2.

The output voltage JEV will be explained below.

Current I8 flowing through the emitter of mass control transistor Q8
Considering the characteristics of the operational amplifier (21), 1x −Vcon, r/Rs =
......(6), and the transistor Q I
Current flowing through the collector of s. . Ion”(Vce Vs*+a＞/R4++++++++
17) However, ■□: Current I that becomes the forward voltage between the base and emitter of transistor Q, and also flows through the collector of transistor Q. Since a corresponds to the current I, which ignores the control current Ia in equation (5), τ1ogN/Rtq・” ...= (
8), therefore, the combined current I0 obtained by the second current combining means (28>) is expressed as lo-1°t-(X, .-1,) using equations (6), (7), and (8). = 1cT IogN/R+q+VCONT/R
1(Vcc-vs*ra)/R---・= (
9), so the voltage V appearing at point B of the voltage conversion means (29>) is: V* = (RsVcc + RJsIo)/(R
s + Rs) ・” ”・= (10),
As is clear from equation (10), the output voltage V.

has a characteristic with two parameters: absolute temperature T and control voltage V008. Especially the control Wt pressure V
When cONA is used as a parameter, it is possible to easily obtain an output voltage V with a constant temperature gradient as shown in FIG. Specifically, the control voltage V. When ONT is a predetermined value, the fourth
Assuming that the characteristics of absolute temperature T and output voltage V shown by the solid line in the figure can be obtained, if the control voltage VCONT is made smaller than a predetermined value, the characteristics shown by the dashed-dotted line in Figure 4 can be obtained, and the control voltage If V C0NT is made larger than a predetermined value, the characteristics shown by the broken line will be obtained.

In addition, the current I8 in equation (6), the current I00 in equation (7), and the current ■ in equation (8>).7 are the power supply voltage V.C% Voltage, resistance (17) (1B) (19) (24) <27) (3
It is also possible to achieve a higher degree of stabilization by considering temperature characteristics such as 0) and (31). Further, in this embodiment, the case where the circuit of the present invention is used in a driver array of an LED printer has been described, but it goes without saying that the present invention is not limited to this.

As described above, according to the present invention, by simply making the control voltage Vcost variable, the output voltage V can have a so-called linear shape with a constant temperature gradient with respect to the absolute temperature T.

can be easily obtained. Further, since the circuit of the present invention does not require a complicated circuit configuration for temperature compensation, reliability is improved, it is suitable for integration into an IC, and costs can be reduced. In particular, when the circuit of the present invention is integrated into an IC, it can contribute to miniaturization of the chip and improvement of the degree of integration.

(G) Effects of the Invention According to the present invention, the output characteristics of the voltage conversion means with respect to temperature can be easily controlled simply by making the control voltage variable.In other words, the circuit of the present invention has a complicated circuit configuration for temperature compensation. Since there is no need for this circuit, reliability is improved, it is suitable for IC implementation, and costs can be reduced.Especially when the circuit of the present invention is implemented as an IC, it contributes to miniaturization of the chip and improvement of the degree of integration. It will be possible.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a temperature compensation circuit of the present invention, FIG. 2 is a diagram showing a driver array of a conventional LED printer, FIG. 3 is a circuit diagram showing a conventional temperature compensation circuit, and FIG. 4 is a diagram showing a temperature compensation circuit of the present invention. FIG. 3 is a characteristic diagram showing output voltage characteristics. (16')...First constant current source, (23)...Second constant current source, <25)...First current combining means,
(26)...Third constant current source, <28>...Second current combining means, <29>...Voltage converting means.

Claims (3)

[Claims] (1) A first constant current source whose current amount is controlled based on a control voltage, a second constant current source whose current amount is fixed, and the first constant current source and the second constant current source. a third constant current source whose current amount depends on temperature changes; and a third constant current source whose current amount depends on temperature changes; a second current synthesizing means for synthesizing the current; and a voltage converting means for converting the output of the second current synthesizing means into a voltage, and controlling the output characteristic of the voltage converting means with respect to temperature by the control voltage. Features a temperature compensation circuit. (2) a first constant current source whose current amount is controlled based on a control voltage; a second constant current source whose current amount is fixed; and the first constant current source and the second constant current source. a third constant current source whose current amount depends on temperature changes; and a third constant current source whose current amount depends on temperature changes; comprising a second current combining means for combining, and a voltage converting means for converting the output of the second current combining means into a voltage, maintaining a constant temperature gradient of the output voltage obtained from the voltage converting means, and A temperature compensation circuit characterized in that the output voltage is linearly controlled by the control voltage. (3) A printing device comprising the temperature compensation circuit according to claim (1) or (2).