JPH07295659A - Peltier element drive circuit - Google Patents

Abstract

PURPOSE:To reduce power consumption and alorific value nearby a Peltier element. CONSTITUTION:An error amplifier 4a outputs the difference between the output of an amplifier 3, which amplifies the forward voltage Vf across a diode 1, and a voltage Vref. A comparator 4c compares a triangular voltage Vt, generated by an oscillator 4b, with a voltage Ve. A voltage Vc is in a pulse shape and used for on/off control over a transistor(TR) 5. As the temperature of the Peltier element 6 rises, the voltage Vf drops and the ON time of the TR 5 becomes long, so that the time wherein a current is supplied to the Peltier element 6 becomes long. As the temperature falls, the time wherein the current is supplied to the Peltier element 6 becomes short. The TR 5, therefore, operates as a switch, so the power consumption of the TR 5 is reducible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Peltier element drive circuit for controlling a cooling temperature of a Peltier element by supplying a drive current to the Peltier element for cooling an infrared sensor.

[0002]

2. Description of the Related Art Conventionally, there is an infrared camera as a device capable of measuring the temperature distribution of an object, and the infrared sensor of this camera is called a quantum type which detects infrared rays by capturing infrared rays as photons and converting them into physical quantities. However, this quantum infrared sensor requires cooling to an extremely low temperature. Further, also in the CCD image pickup device, the S / N ratio can be improved by reducing the dark current when cooled. As a method used for cooling these sensors, there is an electronic cooling method, which cools by passing an electric current through a Peltier element utilizing the Peltier effect.

FIG. 3 is a block diagram of a conventional Peltier element drive circuit for supplying a current to the Peltier element to control the cooling temperature of the Peltier element. Reference numeral 1 is a diode serving as a temperature sensor, 2 is a constant current source for supplying a constant current to the diode 1, 13 is an amplifier for amplifying the forward voltage Vf of the diode 1, and 14 is a transistor described later based on the output of the amplifier 13. Current control circuit to control the base voltage of
Reference numeral 5 is a transistor as a current amplifier for supplying a drive current to the Peltier element 6.

Next, the operation of such a Peltier element driving circuit will be described. The diode 1 and the Peltier element 6 have an integrated structure, and a constant current is supplied from the constant current source 2 to the diode 1. When the temperature of the Peltier element 6 changes, the forward voltage Vf between the anode and the cathode of the diode 1 changes at a rate of about −2 mV / ° C., so that the cooling temperature of the Peltier element 6 can be known from the forward voltage Vf. ing. Then, the current control circuit 14
Controls the base voltage of the transistor 15 based on the output of the amplifier 13 that amplifies this voltage Vf to control the Peltier element 6
Is supplying current to.

Here, when the temperature of the Peltier element 6 rises, the forward voltage Vf decreases, and the current control circuit 14 raises the base voltage of the transistor 15 to increase the current flowing through the Peltier element 6. Conversely, when the temperature of the Peltier element 6 decreases, the voltage Vf increases, and the current control circuit 14 reduces the current flowing through the Peltier element 6. In this way, the cooling temperature of the Peltier element 6 is kept constant. At this time, the drive voltage Va applied to the collector of the transistor 15 is 5V, the emitter voltage, that is, the voltage applied to the Peltier element 6 is 3V,
If the drive current supplied to the Peltier element 6 is 1 A,
The power consumption of the transistor 15 is (5V-3V) × 1A =
It becomes 2W.

[0006]

Although the conventional Peltier element driving circuit controls the driving of the Peltier element as described above, there is a problem that the power consumption of the transistor for supplying the driving current to the Peltier element is large. As a result, there is a problem that the transistor generates extra heat in the vicinity of the Peltier element for cooling. In order to solve the above problems, it is an object of the present invention to provide a Peltier element drive circuit that can reduce power consumption and the amount of heat generated in the vicinity of the Peltier element.

[0007]

According to the present invention, there is provided a temperature sensor for measuring the temperature of a Peltier element and outputting the result as a voltage, an amplifier for amplifying the output voltage of the temperature sensor, and a drive current supplied to the Peltier element. It has a switching element for performing on / off control and a control circuit for controlling the on / off time of this switching element based on the output of the amplifier so that the output voltage of the temperature sensor becomes constant.

[0008]

According to the present invention, the output voltage of the temperature sensor is amplified by the amplifier and input to the control circuit, and the control circuit controls the switching element so that the output voltage of the temperature sensor becomes constant. The cooling temperature is constant.

[0009]

FIG. 1 is a block diagram of a Peltier element drive circuit showing an embodiment of the present invention, FIG. 2 is a diagram showing signal waveforms of respective parts in this Peltier element drive circuit, and the same parts as in FIG. The same reference numerals are attached. 3 is diode 1
An amplifier for amplifying the forward voltage Vf of
A PWM control circuit 5 for performing on / off control of a switching element, which will be described later, on the basis of the output of 1 is a transistor serving as a switching element for performing on / off control of a drive current supplied to the Peltier element 6.

4a is the output of the amplifier 3 and the reference voltage V
An error amplifier that outputs a difference from ref as an output voltage Ve, 4b is an oscillator that generates a triangular wave voltage Vt, 4c is a comparator that compares the voltage Ve and the triangular wave voltage Vt, and 4d is an output transistor.

Next, the operation of such a Peltier element driving circuit will be described. The configurations of the diode 1 and the Peltier element 6 are exactly the same as in the example of FIG.
The forward voltage Vf is amplified. The error amplifier 4a in the PWM control circuit 4 outputs the difference between the output voltage of the amplifier 3 and the reference voltage Vref as the output voltage Ve. Here, the reference voltage Vref is set so that a desired cooling temperature can be obtained by the Peltier element 6 at a certain forward voltage Vf, for example.

Next, the oscillator 4b generates a triangular wave voltage Vt as shown in FIG. 2A, and the comparator 4c compares the triangular wave voltage Vt with the output voltage Ve of the error amplifier 4a. As a result, the output voltage Vc of the comparator 4c is shown in FIG.
As shown by the solid line, the voltage Ve becomes “H” level during the period equal to or higher than the triangular wave voltage Vt, and becomes “L” level during the period below.
The output transistor 4d is turned on when the voltage Vc is at "H" level.

Therefore, the base voltage Vb of the transistor 5 has a waveform as shown by the solid line in FIG. 2 (c). To
During the period of n, the transistor 5 is turned on, a drive current flows from the transistor 5 to the Peltier element 6, and the Peltier element 6 cools. Further, during the period of Toff, the transistor 5 is turned off, the supply of the drive current is stopped, and the cooling by the Peltier element 6 is also stopped.

In the Peltier element drive circuit for performing such switching control, the forward voltage Vf decreases as the temperature of the Peltier element 6 rises, so that the error amplifier 4a.
Output voltage Ve decreases as shown by the broken line in FIG. As a result, the output voltage Vc of the comparator 4c is shown in FIG.
As shown by the broken line in (b), the period of "H" level becomes shorter and the period of "L" level becomes longer, and the base voltage Vb of the transistor 5 becomes Ton as shown by the broken line in FIG. The period becomes longer.

Therefore, since the time for supplying the drive current to the Peltier element 6 becomes long, the time for the Peltier element 6 to cool becomes long, and as a result, the temperature rise of the Peltier element 6 is corrected and the temperature is kept constant. Further, when the temperature of the Peltier element 6 decreases, the forward voltage Vf increases, and the error amplifier 4
Since the voltage Ve of "a" becomes higher than the solid line in FIG. 2A, the time for cooling the Peltier element 6 is shortened by the operation opposite to the above, and as a result, the temperature is kept constant. By the switching control as described above, the Peltier element drive control similar to the example of FIG. 3 can be realized.

Since the transistor 5 operates as a switch in this embodiment, the collector-emitter voltage when the transistor 5 is on is about 0.2 V, and the drive current supplied to the Peltier element 6 is 1 A. The power consumption of the transistor 5 is 0.2 V × 1 A = 0.2 W, which is lower than that in the example of FIG. 3, and the driving voltage Vd applied to the collector of the transistor 5 is 3 V which is the rating of the Peltier element 6. It can be lowered to the extent.
Although the transistor is used as the switching element in the present embodiment, a FET may be used.

[0017]

According to the present invention, the control circuit controls ON / OFF of the switching element to realize the same Peltier element drive control as the conventional one in which the cooling temperature of the Peltier element is kept constant. Since the power consumption can be reduced by using the element, the amount of heat generated in the vicinity of the Peltier element can be reduced. Further, since the drive voltage applied to the switching element can be lowered, the battery voltage can be reduced when a battery is used as the power source, for example.

[Brief description of drawings]

FIG. 1 is a block diagram of a Peltier element drive circuit showing an embodiment of the present invention.

FIG. 2 is a diagram showing signal waveforms of respective parts in the Peltier element drive circuit of FIG.

FIG. 3 is a block diagram of a conventional Peltier element drive circuit.

[Explanation of symbols]

1 ... Diode, 2 ... Constant current source, 3 ... Amplifier, 4 ... PW
M control circuit, 5 ... Transistor, 6 ... Peltier element, 4
a ... error amplifier, 4b ... oscillator, 4c ... comparator, 4d ...
Output transistor.

Claims (1)

[Claims] 1. In a Peltier element drive circuit for controlling a cooling temperature of a Peltier element by a drive current supplied to the Peltier element, a temperature sensor for measuring the temperature of the Peltier element and outputting the result as a voltage, and an output voltage of this temperature sensor. A switching element for controlling on / off of a driving current supplied to the Peltier element, an on / off time of the switching element, and an output voltage of the temperature sensor based on an output of the amplifier. And a control circuit for controlling so as to be constant.