Peltier element and drive circuit therefor

Abstract: A drive circuit drives an electronic device (1) that converts electric power into light or heat energy. The drive circuit has a switch (2) connected to the electronic device in series, and a control circuit (3) for providing, in response to an input control signal, a pulse modulation signal for controlling the switch (2). The frequency of the pulse modulation signal is higher than the response frequency of the electronic device. Alternatively, the drive circuit may have first to fourth switches (6,7,8,9) disposed on both sides of the electronic device (1), for passing a current in different directions through the electronic device, and a control circuit (10) for controlling the switches to change the direction and magnitude of the average of the current flowing through the electronic device in response to an input control signal.

Description: The present invention relates to an arrangement of a Peltier element and a drive circuit. Examples of electronic devices that convert electric power into light or heat energy are direct-current driven laser diodes such as pump laser diodes for optical fiber amplifiers, and Peltier elements. These devices require a high-output drive circuit, which must be compact and operate on low power. Conventional drive circuits for the laser diodes and Peltier elements usually employ an analog control circuit composed of one or more bipolar transistors or field effect transistors (FETs). The analog control circuit is connected to a power source and provides the laser diode or Peltier element with a drive current. Each bipolar transistor or FET of the analog control circuit always consumes a product of the drive current and a voltage applied to both ends of the transistor. This large power consumption deteriorates the efficiency of the drive circuit, requires a high voltage to be applied to the ends of each transistor, increases the size of each transistor, and decreases the space factor of the drive circuit. An object of the present invention is to provide a compact and power saving drive circuit for a Peltier element. EP-A-0 308 358 discloses a control circuit for controlling an H-bridge reversible DC electric motor. When the direction of rotation of the motor is to be reversed, the control circuit controls the switches of the H-bridge by temporarily replacing the original command signal with pulse signals to effect dynamic braking of the motor followed by acceleration in the reverse direction, after which the motor runs in the reverse direction powered by DC of opposite polarity. According to the invention there is provided an arrangement of a Peltier element and a drive circuit, said drive circuit comprising first, second, third and fourth switches disposed on both sides of the Peltier element, for passing a DC drive current in different directions through the Peltier element, and a control circuit for controlling the switches to change the direction of the drive current flowing through the Peltier element in response to an input control signal (CS), said Peltier element being a heating and cooling device arranged to convert the DC drive current into heat energy and the control circuit being operable for selectively controlling the switches to cyclically change the direction and magnitude of the average of the drive current flowing through the Peltier element in response to said input control signal (CS). The invention will be better understood by referring, by way of example, to the accompanying drawings, in which:- Figure 1 is a circuit diagram showing a drive circuit for an electronic device, according to a prior art; Fig. 2 is a view showing the characteristics of a laser diode; Fig. 3 is a circuit diagram showing a drive circuit according to another prior art; Fig. 4 is a view explaining the operation of the drive circuit of Fig. 3; Fig. 5 is a block diagram showing one form of drive circuit for an electronic device, according to the present invention, where the electronic device is a Peltier element; Fig. 6 is a circuit diagram showing a drive circuit for a Peltier element, according to a first embodiment of the present invention; Fig. 7 is a timing chart showing the operation of the drive circuit of Fig. 6; Fig. 8 is a circuit diagram showing a drive circuit for a Peltier element, according to a second embodiment of the present invention; Fig. 9 is a timing chart showing the operation of the drive circuit of Fig. 8. Fig. 10 is a circuit diagram showing a drive circuit for a Peltier element, according to a third embodiment of the present invention; Fig. 11 is a timing chart showing the operation of the drive circuit of Fig. 10; Fig. 12A is a circuit diagram showing a modification of the drive circuit of Fig. 10; Fig. 12B is a circuit diagram showing another modification of the drive circuit of Fig. 10; Fig. 13 is a circuit diagram showing a drive circuit for a Peltier element, according to a fourth embodiment of the present invention; Fig. 14 is a timing chart showing an operation of the drive circuit cf Fig. 13; Fig. 15A is a circuit diagram showing a modification of the drive circuit of Fig. 13; and Fig. 15B is a circuit diagram showing another modification of the drive circuit of Fig. 13. For a better understanding of the preferred embodiments of the present invention, the problems of prior arts will be explained with reference to the drawings. Figure 1 shows a drive circuit according to a prior art. This drive circuit drives a pump laser diode of an optical fiber amplifier. Figure 2 shows the I-L characteristics of the laser diode. This drive circuit involves the laser diode (LD) 1, a bipolar transistor (or a field effect transistor (FET)) 21, and an optical fiber 22. To emit a required light beam, the laser diode 1 must receive a relatively large drive current I P . The drive current I P is analogically controlled by the bipolar transistor (or FET) 21 in response to an input analog control voltage V C . The transistor 21 of the analog control system always consumes electric power of "I P x V CE ." To cover this power consumption, a power source voltage must be high, and the bipolar transistor (or FET) must be of large power. This results in deteriorating the efficiency and space factor of the drive circuit. Figure 3 shows another conventional drive circuit. This circuit drives a Peltier element 1. The drive circuit includes an analog control circuit 23, P-channel MOSFETs 24 and 26, and N-channel MOSFETs 25 and 27. Figure 4 explains the operation of the drive circuit of Fig. 3. When an input analog control voltage V C rises to a power source voltage +V, an output analog control voltage V 1 falls from the voltage +V to zero, and an analog control voltage V 2 rises from zero to the voltage +V. Consequently, the FETs 24 and 25 become conductive to pass a drive current I P in a positive direction through the Peltier element 1, thereby heating the Peltier element 1. When the input voltage V C falls below zero, an output analog control voltage V 3 falls from the voltage +V to zero, and an analog control voltage V 4 rises from zero to the voltage +V. Consequently, the FETs 26 and 27 become conductive to pass the drive current I P in a reverse direction through the Peltier element 1, thereby cooling the Peltier element 1. According to this analog control system, each conductive FET consumes electric power of "I P x V DS ." To cover this power consumption, a large power source voltage is required. Namely, each FET (or bipolar transistor) must be of large power. This results in deteriorating the efficiency and space factor of the drive circuit. In this way, the conventional drive circuits analogically control a drive current flowing through an electronic device. This technique consumes large power to lower driving efficiency. Since a high power source is needed to cover the power consumption, the drive circuit must employ large-power elements, which deteriorate the space factor of the drive circuit. Figure 5 shows a drive circuit for an electronic device in the form of a Peltier element, the drive circuit and Peltier element being in accordance with the invention. This drive circuit involves the electronic device 1 for converting electric power into light or heat energy, first, second, third, and fourth switches 6, 7, 8, and 9 disposed on both sides of the electronic device 1, for passing a current in different directions through the electronic device 1, and a control circuit 10 for controlling the switches 6 to 9 in response to an input control signal CS to change the magnitude and direction of the average of the current flowing through the electronic device 1. When the control circuit 10 controls the switches 6 to 9 in response to the control signal CS to change the direction and magnitude of the average of the current passing through the electronic device 1, the switches 6 to 9 consume ignorable electricity. This results in reducing a power source voltage as well as the capacity of the switches 6 to 9. The control circuit 10 may control the switches 6 to 9 such that a current flows in opposite directions through the electronic device 1 in response to a pulse modulation signal whose frequency is higher than the response frequency of the electronic device 1 and such that the direction and magnitude of the average of the current are changed in response to the control signal CS. The control circuit 10 causes a current to flow in a forward or reverse direction through the electronic device 1 in response to the control signal CS, and controls the switches 6 or 7 and 8 or 9 to change the direction and magnitude of the average of the current in response to a pulse modulation signal whose frequency is higher than the response frequency of the electronic device 1. As shown in Fig, 10, the drive circuit may have inductors 11 and 12 connected among the switches 6 or 7 and 8 or 9 in series, and catch diodes 13 and 14 for feeding energy accumulated in the inductors 11 and 12 back to a power source circuit along a route through the electronic device 1 when the switches 6 or 7 and 8 or 9 are turned OFF. As shown in Fig. 13, the drive circuit may have an inductor 15 connected at least to an end of the electronic device 1 in series, and catch diodes 16 and 17 for feeding energy accumulated in the inductor 15 back to a power source circuit along a route through the electronic device 1 when a primarily acting one of the switches 6 to 9 is turned OFF. The electronic device 1 is a Peltier element. The pulse modulation signal may be a PWM signal, a PFM signal, or a PAM signal. Preferred embodiments of the present invention will be explained in detail with reference to the drawings. Like reference marks represent like parts through the drawings. Figure 6 shows a drive circuit and Peltier element according to a first embodiment of the present invention. This circuit involves a Peltier element 1, a control circuit 10, a sawtooth oscillator 10-1 composed of a CMOS circuit having a frequency of, for example, 200 KHz, a comparator (CMP) 10-2, an inverter (I) 10-3, P-channel MOSFETs 6 and 8, and N-channel MOSFETs 7 and 9. The comparator 10-2 compares an input analog control voltage V C with a sawtooth signal V S from the sawtooth oscillator 10-1, and provides a PWM signal V G and an inverted signal V G '. The PWM signal V G is positive when V S >V C . When the V G is zero, the FET 6 is ON and the FET 9 is OFF. At this time, the inverted signal V G ' is positive, and therefore, the FET 8 is OFF and FET 7 is ON. As a result, a current I P flows in a forward direction through the Peltier element 1. When the signal V G is positive, the FET 6 is OFF and FET 9 is ON. At this time, the inverted signal V G ' is zero, and therefore, the FET 8 is ON and the FET 7 is OFF. As a result, the current I P flows in a reverse direction through the Peltier element 1. Figure 7 is a timing chart showing the operation of the drive circuit of Fig. 6. When the input analog control voltage V C is at an intermediate level, the PWM signal V G achieves a positive duty ratio of 50%. Accordingly, the current I P equally flows in both directions through the Peltier element 1, and therefore, the average I A of the current I P is zero. Namely, the Peltier element 1 is equally heated and cooled to balance the temperature thereof. When the control voltage V C exceeds the intermediate level, the positive duty ratio of the PWM signal V G decreases, while the positive duty ratio of the inverted signal V G ' increases. As a result, the current I P flows in the forward direction for a longer time through the Peltier element 1, to heat the Peltier element 1. When the control voltage V C drops below the intermediate level, the positive duty ratio of the PWM signal V G increases, and the positive duty ratio of the inverted signal V G ' decreases. As a result, the current I P flows in the reverse direction for a longer time through the Peltier element 1, to cool the Peltier element 1. Figure 8 shows a drive circuit according to the second embodiment of the present invention. This circuit includes a Peltier element 1, a control circuit 10, a sawtooth oscillator 10-4, comparators (CMPs) 10-5 to 10-8, an inverting amplifier (AMP) 10-9, and a voltage follower (AMP) 10-10. Figure 9 is a timing chart showing the operation of the drive circuit of Fig.8. The comparator 10-8 turns ON a FET 7 when V C >0. The comparator 10-6 compares an input analog control voltage V C from the voltage follower 10-10 with a triangular signal V S from the oscillator 10-4 and provides a PWM signal V 1 , which is zero if V S <V C . When the control voltage V C is positive and close to zero, a drive current I P slightly flows in a forward direction through the Peltier element 1. When the control voltage V C increases, the 0V duty ratio of the PWM signal V 1 increases from about 0% to 100% at the maximum. As a result, the drive current I P flows in the forward direction for a longer time through the Peltier element 1. The average I A of the drive current I P flowing through the Peltier element 1, therefore, increases to heat the Peltier element 1. When V C <0, the comparator 10-7 turns ON a FET 9. The comparator 10-5 compares an inverted control voltage V C ' from the inverting amplifier 10-9 with the triangular signal V S from the oscillator 10-4 and provides a PWM signal V 3 , which is zero if V S <V C '. When the control voltage V C drops below zero, the 0V duty ratio of the PWM signal V 3 increases from about 0% to 100% at the maximum. As a result, the drive current I P flows in a reverse direction for a longer time through the Peltier element 1. As a result, the average I A of the drive current I P flows in the reverse direction to cool the Peltier element 1. When the control voltage V C is negative and close to zero, the drive current I P only slightly flows in the reverse direction through the Peltier element 1. The drive circuit according to the second embodiment effectively drives the Peltier element 1. In one example, an average current (I A ) of one ampere flows through the Peltier element 1 when the Peltier element 1 has a resistance (R P ) of two ohms, each FET has an ON resistance (R ON ) of 0.2 ohms, and a source voltage (+V) is five volts. In this case, the conventional drive circuit of Fig. 3 consumes five watts in total (P 2 ) to drive the Peltier element 1. On the other hand, the drive circuit of the second embodiment of Fig. 8 consumes only 2.4 watts in total (P 1 ) to drive the Peltier element 1. Namely, the drive circuit of the second embodiment can drive the Peltier element 1 with 48% electric power of the prior art. Although the prior art of Fig. 3 must employ a FET of about one watt class, the second embodiment may employ a compact FET of 0.4watt class. In the above embodiment, the FETs 7 and 9 are used to regulate the direction of a current, and the FETs 6 and 8 are used to turn ON and OFF the current. Instead, the FETs 6 and 8 may be used to regulate the direction of a current, and the FETs 7 and 9 may be used to turn ON and OFF the current. Figure 10 shows a drive circuit according to the third embodiment of the present invention. This circuit involves inductors (Ls) 11 and 12, and catch diodes (Ds) 13 and 14. When a FET 6 is turned ON with a FET 7 being ON, a drive current I P flows in a forward direction through a Peltier element 1 via the coil 11. When the FET 6 is turned OFF, the coil 11 discharges accumulated energy, so that the drive current I P continuously flows in the forward direction through the Peltier element 1 via the catch diode 13. When a FET 8 is turned ON with a FET 9 being ON, the drive current I P flows in a reverse direction through the Peltier element 1 via the inductor 12. When the FET 8 is turned OFF, the inductor 12 discharges accumulated energy, so that the drive current I P continuously flows in the reverse direction through the Peltier element 1 via the catch diode 14. Figure 11 is a timing chart showing the operation of the drive circuit of the third embodiment. The operation of the control circuit 10 of this embodiment is the same as that of the second embodiment. According to the third embodiment, the drive current I P continuously flows in the forward or reverse direction through the Peltier element 1 even after the FET 6 or 8 is turned OFF, to smooth the drive current I P . If the FET 7 is turned OFF while the inductor 11 is discharging accumulated energy, the FET 9 is turned ON to continuously discharge the accumulated energy from the inductor 11. This is also true for the inductor 12. Accordingly, the Peltier element 1 is analogically controlled with the smoothed drive current I P . The total power consumption (P 1 ) of the drive circuit of the third embodiment is 2.7 watts. Namely, this drive circuit drives the Peltier element 1 with 54% electric power of the prior art. The third embodiment may employ a compact FET of 0.5watt class. Figures 12A and 12B show modifications of the third embodiment. In Fig. 12A, the switching of FETs 7 and 9 is controlled, and in Fig. 12B, the switching of FETs 6 and 9 is controlled. In Fig. 12A, the FET 7 is turned ON with a FET 6 being ON, and a drive current I P flows in a forward direction through an electronic device 1, in the form of a Peltier element via an inductor 11. When the FET 7 is turned OFF, the inductor 11 discharges accumulated energy, so that the drive current I P continuously flows in the forward direction through the electronic device 1 via a catch diode 13. When the FET 9 is turned ON with a FET 8 being ON, the drive current I P flows in a reverse direction through the electronic device 1 via an inductor 12. When the FET 9 is turned OFF, the inductor 12 discharges accumulated energy, so that the drive current I P continuously flows in the reverse direction through the electronic device 1 via a catch diode 14. In Fig. 12B, the FET 6 is turned ON with a FET 7 being ON, and a drive current I P flows in a forward direction through the electronic device 1 via an inductor 11. When the FET 6 is turned OFF, the inductor 11 discharges accumulated energy, so that the drive current I P continuously flows in the forward direction through the electronic device 1 via a catch diode 13. When the FET 9 is turned ON with a FET 8 being ON, the drive current I P flows in a reverse direction through the electronic device 1 via an inductor 12. When the FET 9 is turned OFF, the inductor 12 discharges accumulated energy, so that the drive current I P continuously flows in the reverse direction through the electronic device 1 via a catch diode 14. In this way, the third embodiment allows various modifications. Figure 13 shows a drive circuit according to the fourth embodiment of the present invention. This drive current involves an inductor (L) 15 and catch diodes (Ds) 16 and 17. When a FET 6 is turned CN with a FET 7 being ON, a drive current I P flows in a forward direction through a Peltier element 1 via the inductor 15. When the FET 6 is turned OFF, the inductor 15 discharges accumulated energy, so that the drive current I P continuously flows in the forward direction through the Peltier element 1 via the catch diode 16. When a FET 8 is turned ON with a FET 9 being ON, the drive current I P flows in a reverse direction through the Peltier element 1 via the inductor 15. When the FET 8 is turned OFF, the inductor 15 discharges accumulated energy, so that the drive current I P continuously flows in the reverse direction through the Peltier element 1 via the catch diode 17. The fourth embodiment employs only one coil, to simplify the drive circuit and improve the space factor thereof, compared with the third embodiment. Figure 14 is a timing chart showing the operation of the drive circuit of thefourth embodiment. The operation of the control circuit 10 of this embodiment is the same as that of the second embodiment. According to the fourth ambodiment, the drive current I P continuously flows through the Peltier element 1 in the forward or reverse direction even after the FET 6 or 8 is turned OFF, to smooth the drive current I P . Figures 15A and 15B show modifications of the fourth embodiment. In Fig. 15A, the switching of FETs 7 and 9 is controlled, and in Fig. 15B, the switching of FETs 6 and 9 is controlled. In Fig. 15A, the FET 7 is turned ON with a FET 6 being ON, and a drive current I P flows in a forward direction through an electronic device 1 via an inductor 15. When the FET 7 is turned OFF, the inductor 15 discharges accumulated energy, so that the drive current I P continuously flows in the forward direction through the electronic device 1 via a catch diode 16. When the FET 9 is turned ON with a FET 8 being ON, the drive current I P flows in a reverse direction through the electronic device 1 via the inductor 15. When the FET 9 is turned OFF, the inductor 15 discharges accumulated energy, so that the drive current I P continuously flows in the reverse direction through the electronic device 1 via a catch diode 17. In Fig. 15B, the FET 6 is turned ON with a FET 7 being ON, and a drive current I P flows in a forward direction through an electronic device 1 via an inductor 15. When the FET 6 is turned OFF, the inductor 15 discharges accumulated energy, so that the drive current I P continuously flows in the forward direction through the electronic device 1 via a catch diode 16. When the FET 9 is turned ON with a FET 8 being ON, the drive current I P flows in a reverse direction through the electronic device 1 via the inductor 15. When the FET 9 is turned OFF, the inductor 15 discharges accumulated energy, so that the drive current I P continuously flows in the reverse direction through the electronic device via a catch diode 17. In this way, the fourth embodiment allows various modifications. Although the first to fourth embodiments provide a PWM signal according to the input analog control voltage V C , they may provide a PFM signal. Alternatively, they may change the power source voltage +V according to the control voltage V C , to provide a PAM signal. Any one of the drive circuits described above may be assembled into a feedback loop, which provides constant light or heat output. The drive circuits described above have first to fourth switches 6 to 9 disposed on both sides of an electronic device 1 so that a current may flow in both directions through the electronic device (Peltier element) 1, and a control circuit 10 for controlling the switches 6 to 9, to change the direction and magnitude of the average of the current flowing through the electronic device 1, in response to an input control signal CS. This drive circuit is compact, works on a low voltage, consumes low power, and is applicable for an electronic device that works with a bidirectional current. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: An arrangement of a Peltier element and a drive circuit, said drive circuit comprising: first, second, third and fourth switches (6, 7, 8, 9) disposed on both sides of the Peltier element (1), for passing a DC drive current in different directions through the Peltier element (1); and a control circuit (10) for controlling the switches (6, 7, 8, 9) to change the direction of the drive current flowing through the Peltier element (1) in response to an input control signal (CS); said Peltier element being a heating and cooling device arranged to convert the DC drive current into heat energy and the control circuit being operable for selectively controlling the switches (6, 7, 8, 9) to cyclically change the direction and magnitude of the average of the drive current flowing through the Peltier element in response to said input control signal (CS). An arrangement according to claim 1, characterised in that the control circuit (10) is arranged to control the switches (6 to 9) such that the drive current flows in both directions through the Peltier element (1) according to a pulse modulation signal whose frequency is higher than the response frequency of the Peltier element (1), and such that the direction and magnitude of the average of the drive current are changed in response to the control signal (CS). An arrangement according to claim 1, characterised in that the control circuit (10) is arranged to cause the drive current to flow in a forward or reverse direction through the Peltier element (1) in response to the control signal (CS), and to change the magnitude of the average of the drive current by controlling the switches (6 or 7 and 8 or 9) along a route for transmitting the drive current according to a pulse modulation signal whose frequency is higher than the response frequency of the Peltier element (1). An arrangement according to claim 3, characterised by: inductors (11, 12) connected among the switches (6 or 7 and 8 or 9) in series; and catch diodes (13, 14) for feeding energy accumulated in the inductors (11, 12) back to a power source circuit along a route through the Peltier element (1) when the switches (6 or 7 and 8 or 9) are turned OFF. An arrangement according to claim 3, characterised by: an inductor (15) connected at least to an end of the Peltier element (1) in series; and catch diodes (16, 17) for feeding energy accumulated in the inductor (15) back to a power source circuit along a route through the Peltier element (1) when the switches (6 or 7 and 8 or 9) are turned OFF. An arrangement according to claim 2, characterised in that the pulse modulation signal is a PMW signal, a PFM signal, or a PAM signal.

Inventors: MIYAKI YUJI, SHIMA MICHIKAZU, MIYAKI, YUJI, SHIMA, MICHIKAZU, Miyaki, Yuji, c/o Fujitsu Limited, Shima, Michikazu, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1993
Main classification: H02M3
IPC codes: G05D23, H02M3, H05B6, H02M7, H01S5, G05D25, H05B33, G05B11, H01L35, H01S3