JPS5937701Y2 - Photo sensor temperature compensation circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to a temperature compensation circuit that compensates for variations in brightness due to temperature changes in semiconductor light-emitting elements in photosensors, and maintains a constant level of brightness at all times. We propose a temperature compensation circuit for a photosensor that can perform temperature compensation for a photosensor with a single circuit, and can also compensate for a constant voltage circuit for driving a light emitting element.

Transmissive type and reflective type photosensors are known, and their configuration is simpler and cheaper than mechanical position detection devices, so they are used for position detection in various devices. Widely used.

FIG. 1 is a perspective view showing the main parts of a dot printer equipped with a large number of photosensors.

In the drawing, 1 is a print head, 2 is a sensor unit, 3 is mylar, 3A is a dot mark printed on the mylar 3, 4 is a card, 4A is a mark for detecting the print position printed on the card 4, and 5 is a mark printed on the card 4. Mark sensor, 6
The card feeding roller 7 is a rotating disk coaxially connected to the roller 6, and 8 is a slit sensor.

In this dot printer, various photosensors such as the sensor unit 2, mark sensor 5, and slit sensor 8 detect the position of the carrier, the print position of the card, or count the marks.

FIG. 2 is a schematic cross-sectional view of the sensor unit 2.
DI-3 is a diode, PH-'rr1 to 3 are phototransistors, and 2A is a dot sensor. -12
B and 2C also show sensors that detect the position of the carrier by marks printed on Mylar 3.

3A shows the output circuit of the dot sensor 2A, and FIG. 3B shows the output ea of the operational amplifier OP.

When the dot sensor 2A detects a don't-miss pattern, its detection output changes in the form of a sine wave as shown in FIG. The letters I F T+ are printed like A.

Furthermore, if both the positive and negative peak values are set as dot printing positions, the dots will be printed as shown in FIG. 4B.

In FIGS. 4A and 4B, the solid line indicates the peak value of the black mark, and the one-dot chain line indicates the peak value of the white mark.

However, if the peak value eap of the output ea of the operational amplifier OP changes due to a change in the ambient temperature, as shown in FIG. Print quality will deteriorate due to unevenness.

The influence of such a temperature change also appears in the case of the sensors 2B and 2C for detecting the position of the carrier, and the bias level is relatively changed, making it impossible to accurately detect the position.

Furthermore, the same applies to the mark sensor 5 that detects the mark 4A on the card 4 and the slit sensor 8 that detects the slit of the rotating disk 7.

In order to eliminate such inconveniences, conventional photosensors mainly perform temperature compensation on the light receiving side. For example, two light receiving elements with the same characteristics are used to cancel out brightness fluctuations due to temperature changes, or The light-receiving element was driven at constant voltage or constant current.

When a large number of sensors are used as shown in FIG. 1, each sensor is provided with a circuit for temperature compensation.

On the other hand, the photo sensor temperature compensation circuit of this invention is characterized by performing temperature compensation on the light emitting side of the photosensor.In particular, even when multiple photosensors are used, one compensation circuit is required. It is an object of the present invention to make it possible to compensate the temperature of all light emitting elements by simply using the device, and also to compensate the constant voltage drive circuit at the same time.

FIG. 5 is a block diagram showing an embodiment of the temperature compensation circuit of this invention.

In the drawing, op-1 to 0P-3 are operational amplifiers, Tr
l and Tr2 are transistors, LED is a light emitting diode,
R8-R8 are resistors, RVl and Rv2 are variable resistors, E1-E3 are DC power supplies, and Va-Vd are input/output voltages.

The operational amplifier 0P-1 constitutes a logarithmic converter together with the transistor Tri and the like, and logarithmically converts the input signal Va to generate an output signal vb.

The next operational amplifier 0P-2 inverts and amplifies the input signal vb with resistors R2, R3, and R7, and the operational amplifier 0P-3
constitutes a constant voltage circuit together with the transistor Tr2 and the resistors R4 to R6.

Generally, the voltage at the pn junction of a light emitting diode LED is
As the temperature increases, its brightness decreases.

FIG. 6 is a characteristic diagram showing the relationship between ambient temperature T and brightness of this light emitting diode.

The brightness of the light emitting diode and the current (2) flowing through the p-n junction are expressed by the following equations (1) and (2).

However, K1 and 2 are proportional constant e is the electron charge (1,602X10"9C) and V is p -
The voltage applied to the n-junction is determined by the Hornmann constant (1,380×1O-23J10K
) T is the absolute temperature (0K) In the case of GaAsP, n=2 in the low current region and n=1 in the high current region at m21.

If we convert this formula (1), we get Then, Furthermore, the voltage V applied to the p-n junction is It is expressed as

Further, if the collector current flowing through the transistor is Io, then the reverse saturation current VBE is converted with respect to the base-emitter voltage VBE, and is expressed as follows.

Now, in the circuit of FIG. 5, when input voltage Va is applied, its output vb is the base of transistor Tri.
Since the emitter voltage is output, the above equation (6) is satisfied, and as the temperature T rises, the output vb decreases.

However, it is inverted and amplified by the next inverting amplifier.

That is, as the temperature T rises, the voltage of the output Vc also rises.

As a result, the output voltage Vd of the constant voltage circuit also increases as the temperature T rises, and the current I flowing through the light emitting diode LED also increases.

In this case, the change △■ due to temperature in the forward voltage drop of the light emitting diode LED is calculated by the above equations (5) and (6).
) is supported.

Therefore, the change due to temperature in the voltage ■ applied to the p-n junction of the light emitting diode in equation (4) above, and the base-emitter voltage V in equation (6) in transistor Tr2
If the values of resistors R2, R3, R5, and R6 are determined so that the output Vd is increased by the change in VBE with respect to the change in BE, then as the temperature T rises, the light emitting diode L
The current flowing through the ED is also increased so that constant brightness can be maintained at all times.

Although FIG. 5 shows the case where only one light emitting diode LED is connected, the same applies even when a plurality of light emitting diodes are connected in parallel.

FIG. 7 is a block diagram showing another embodiment of this invention.

In the drawing, 0P-4 and 0P-5 are operational amplifiers, Tr3
are transistors, LED1 to LEDn are light emitting diodes, D is a diode, R9 to R14 are resistors, -E4 and R5 are DC power supplies, and Ve to Vg are input/output voltages.

In the temperature compensation circuit shown in FIG.
-4, and then the n light emitting diodes LED1 to L E
The drive control of Dn is performed.

That is, for example, when the temperature rises, the diode D
If the forward drop voltage VD of is lowered by △V, the input voltage Ve of operational amplifier 0P-4 is Ve"" (R4VD)...
...(9) Maybe Ve-△■=-(R4-(VD-△y))= (E4
+ΔV−VD) ...00), and the output Vf of the operational amplifier 0P-4 in this case increases by ΔV.

As a result, the voltage R12R of the driving part of the light emitting 9 diode LED1 to LEDn
IO Vg also increases by R1°+R13° R9°V".

For example, in the case of germanium diodes,
By selecting the resistance values of the resistors R9R12+R13 so that RIOR12=1, the voltage V of the drive unit due to temperature changes can be reduced.
Fluctuations in g can be canceled out, and a constant brightness can always be maintained.

Note that temperature compensation can be performed in the same manner not only when using a light emitting diode but also when using a phototransistor.

As explained in detail above, the photo sensor temperature compensation circuit of this invention focuses on the fact that the temperature-brightness characteristics of semiconductor light emitting elements such as light emitting diodes and phototransistors change logarithmically, and on the light emitting side of the photosensor,
Control is performed so that fluctuations in voltage applied to a p-n junction of a light emitting diode or the like are compensated for in response to temperature changes.

Therefore, temperature compensation of the constant voltage circuit for driving the light emitting diode and the like can be performed at the same time, and the brightness thereof can always be maintained at a constant level.

Furthermore, it is possible to compensate multiple light emitting diodes, etc. at the same time with one set of temperature compensation circuits, making it extremely easy to configure even when multiple photo sensors are required, such as in the dot printer described earlier. can do.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the main parts of a dot printer equipped with a large number of photosensors, Fig. 2 is a schematic cross-sectional view of the sensor unit shown in Fig. 1, Fig. 3A is an output circuit of the dot sensor, Fig. 3 B is the output signal of the operational amplifier eas. Figure 4 A and B are the letters "F" whose dot printing positions are the peak values of positive and negative, etc.
Fig. 5 is a block diagram showing an embodiment of the temperature compensation circuit of this invention, Fig. 6 is a characteristic diagram showing the relationship between ambient temperature T and brightness of a light emitting diode, and Fig. 7 is a pattern example of this. It is a block diagram showing another embodiment of the invention. In the drawing, 1 is a print hand, 2 is a sensor unit, 3 is my card 2-14, 5 is a mark sensor, 6 is a roller for card feeding, 7 is a rotating disk, 8
is a slit sensor, OP1 to 0P-5 are operational amplifiers,
Tr1 to Tr3 are transistors, LED and LEDI to L
EDn is a light emitting diode, R1-R14 are resistors, RV
1 to Rv2 are variable resistors, E1 to E5 are DC power supplies, and Va=Vg is an input/output voltage.

Claims (1)

[Scope of utility model registration request] A circuit that generates a logarithmically related output signal in response to temperature changes, an amplifier that inverts and amplifies the output of this circuit, and a p-n of a semiconductor light emitting element such as a light emitting diode or a phototransistor that is controlled by the output of this amplifier. 1. A temperature compensation circuit for a photosensor, comprising a constant voltage circuit that applies voltage to a junction, and controlling so that a constant brightness is always maintained by compensating for changes in brightness of a light emitting element due to temperature fluctuations.