JPH0595673A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To make it possible to adapt a converter, as it is, to a load temporarily requiring a large current by adding a power-up circuit capable of temporarily changing and increasing a reference voltage as required, to an overcurrent detecting circuit. CONSTITUTION:A comparison voltage circuit 29 of an overcurrent detection circuit 27 compares a comparison voltage by a load current of a predetermined resistor to a reference voltage of a reference voltage circuit 28; and if a load current increases beyond a rated output current, then a feedback control is performed in such a manner that the current is limited by sending a control signal from an operational amplifier 30 to a control circuit 26. A power-up circuit 31 is connected to the reference voltage circuit 28 of the overcurrent detection circuit 27; this power-up circuit 31 is operated to increase the reference voltage of the overcurrent detection circuit 27, accordingly, the load current is temporarily increased above the rated output current and power is supplied to the load of a large current load. By doing this, the converter is able to respond to a load requiring a large current temporarily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-D which converts a high voltage of a DC power source such as a battery into a predetermined DC voltage and outputs it.
The present invention relates to a C converter, and more particularly to a DC-DC converter to which a means for temporarily increasing the output current when needed is added.

[0002]

2. Description of the Related Art In recent years, the applicant has proposed a system in which a vehicle of a diesel engine is equipped with a retarder control device. In this retarder control system, an induction machine that operates as an electric motor and a generator is mounted on a drive system of a diesel engine, and electric braking is performed by the generation mode control of the induction machine to increase the engine braking effect. The energy is converted into electric energy and regenerated so as to charge the battery. In addition, a basic configuration is that auxiliary acceleration is performed by electric mode control of an induction machine by a battery power source to increase engine output and reduce exhaust gas. On the other hand, the DC power source of the battery in this case can also be used for other purposes. Therefore, it is converted into a predetermined DC voltage by the DC-DC converter and used in various electric components of diesel engines and vehicles. It is designed to supply power. In addition, the electric power used to control such an induction machine is inevitably large, whereas setting it to a large current type requires measures such as thickening the coil of the induction machine and reducing resistance. And increase in electric leakage, which is not preferable. Therefore, the power control system of the induction machine is set to a high voltage type, and therefore the power supply voltage of the battery is also set to a high voltage. Therefore, it is necessary that the DC-DC converter is a constant voltage type capable of efficiently converting a high voltage to a low voltage, and further configured to meet various electrical requirements of electric components. Become.

Conventionally, as described above, the DC-D has been adapted to a large capacity DC power source and has a high efficiency and a relatively large voltage conversion rate.
The C converter is composed of a switching type constant voltage power supply circuit. That is, it is configured by combining a DC-AC inverter with a rectifier circuit, a DC voltage of an input is converted into a high frequency input by a switching circuit having a power transistor, etc., and this high frequency input is transformed by a power transformer to generate a pulsating current output by a diode. It is taken out, rectified by a rectifier circuit of a capacitor, smoothed by a filter circuit of a choke coil, and output a predetermined DC voltage. Further, the switching frequency of the switching circuit is adjusted by the control circuit according to the change of the output voltage to keep the voltage constant.
On the other hand, in this constant voltage type, a protection circuit for preventing an overcurrent is provided in order to prevent an overcurrent from flowing due to a short circuit of an output terminal or the like and destroying various elements.

[0004]

However, in the configuration of the above-mentioned conventional DC-DC converter, the DC voltage is always converted into the rated DC voltage. Further, the current is limited to the rated current or less by the limiting current value of the overcurrent protection circuit, so that a large current temporarily powered up cannot be output. Here, in the diesel engine as described above, a preheat heater is attached to the intake system, and the preheat position is provided before the starter position of the key switch. When the engine is started at a low temperature, power is supplied to the preheating heater for a predetermined time at the preheating position to preheat the intake air, and then the preheater is started at the starter position to favorably perform combustion by spontaneous ignition in the cylinder. Therefore, in the system of the retarder control device, it is conceivable to supply power to the preheat heater by the DC-DC converter at the time of this low temperature start. The electric power required for the preheater in this case is limited to a low temperature and for a short time, but is larger than the electric power of other electric components. Therefore, in order to feed power to the preheater by the above-mentioned conventional DC-DC converter, it is necessary to provide a dedicated conversion circuit for outputting this power, which leads to a complicated structure and high cost.

The present invention has been made in view of the above problems, and its object is to convert it into a rated output voltage and a rated output current for output, and further to exceed the rated output current when necessary. Another object of the present invention is to provide a DC-DC converter that can temporarily output even a large current.

[0006]

In order to achieve this object, the present invention converts a DC voltage input by means of a switching system in a DC-DC converter into a predetermined DC voltage, and a reference voltage in an overcurrent detection circuit. Is a module configured to detect the overcurrent by comparing the reference voltage with the load current and limit the output current to a specified rated current.The overcurrent detection circuit temporarily increases the reference voltage when necessary. The main feature is to add a changing power-up circuit. Then, the power-up circuit is activated to increase the reference voltage of the overcurrent detection circuit, and accordingly, the load current can be temporarily increased to the rated output current or more to supply the load of the large current specification.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the principle of the DC-DC converter of the present invention,
It is a block diagram which shows the Example applied to the diesel engine with a retarder. First, the system of the retarder control device of the diesel engine will be described. The flywheel 2 of the drive system of the diesel engine 1 is equipped with the induction machine 11 that operates as an electric motor and a generator.
Are connected to the transmission 4 and thereafter via the clutch 3.
In the retarder control device 10, the induction machine 11 is connected to the battery 13 via the inverter circuit 12 in a power controllable manner, and the control circuit 14
The inverter circuit 12 supplies battery power to the induction machine 11 and generates an advanced rotating magnetic field in response to the electric mode signal of (1) to operate as an electric motor for auxiliary acceleration. The inverter circuit 12 generates a delayed rotating magnetic field in the induction machine 11 by the power generation mode signal, operates as a generator to electrically brake, and regenerates the electric energy generated at this time to charge the battery 13. It

Next, a power supply system for various electric components by the DC power source of the battery 13 will be described.
A DC-DC converter 20 is connected to 13. This DC-
The positive output side of the DC converter 20 is connected to various electric components 7 and a preheat heater 6 mounted inside the intake pipe 5 of the diesel engine 1. Also, diesel engine 1
The key switch 15 of is OFF, ACC, ON in the rotation direction,
The preheat and starter positions are sequentially arranged.To prevent erroneous operation, the timer output turns on when the preheat position signal is input to the timer circuit 16 for a predetermined time or longer, and the timer output turns off when the starter position signal is input. .. A preheat switch 17 is provided in the circuit of the preheat heater 6 and a power-up switch 18 is provided for the DC-DC converter 20.
The timer circuit 16 is configured to turn these switches 17 and 18 on and off.

The DC-DC converter 20 has a switching circuit 21 connected to the battery 13 in one module 20a, and this switching circuit 21 is connected to a power transformer 22, a rectifier circuit 23, and a filter circuit 24, so that the battery 13 A direct current voltage is converted into a predetermined direct current voltage by a switching method and output. A voltage detection circuit 25 is connected to the output side to obtain the deviation between the output voltage and the rated reference voltage,
Depending on this deviation, the control circuit 26 causes the switching circuit 21
Adjust the switching frequency of. Also, the reference voltage circuit
28, a comparison voltage circuit 29, and an overcurrent detection circuit 27 having an operational amplifier 30 for comparing the two voltages are connected, and the comparison voltage by the load current of a predetermined resistance is compared with the reference voltage, and the load current exceeds the rated output current. When it is increased to 1, the limit signal is output from the operational amplifier 30 to the control circuit 26 to perform feedback control so as to limit the current. Then, the power-up circuit is added to the reference voltage circuit 28 of the overcurrent detection circuit 27.
31 is connected, the power-up switch 18 is connected to the power-up circuit 31, and the power-up circuit 31 is activated by a switch-on signal.

Next, the operation of this embodiment will be described. The retarder control device 10 is controlled in the power generation mode during steady running and braking when the vehicle is running, and the battery 13 is charged by regenerating electric energy generated in the induction machine 11 of the drive system of the diesel engine 1. Then, the power source of the battery 13 is supplied to the induction machine 11 when the retarder control device 10 is controlled in the electric mode during acceleration, and is used for auxiliary acceleration. The DC high voltage of the battery 13 is applied to the DC-DC converter 20.
Is converted into a high frequency input by the switching circuit 21 of the module 20a, converted into a predetermined voltage by the power supply transformer 22, rectified by the rectifier circuit 23, smoothed by the filter circuit 24 and converted into a predetermined low DC voltage. At this time, the output voltage is controlled to a constant voltage, and the current is limited by overcurrent detection.
In this way, rated voltage and current are output. Then, the rated voltage is applied to the electrical component 7, a current according to the load flows, and power is normally supplied, and the battery power source is also used for the electrical component 7 of the low voltage specification. On the other hand, if the key switch 15 is set to the preheat position for a predetermined time at low temperature start, the timer circuit
The preheat switch 17 is turned on by 16 and the preheat circuit is turned on. Further, the power-up switch 18 is turned on and the reference voltage of the overcurrent detection circuit 27 of the module 20a is increased by the power-up circuit 31, so that a current larger than the rated current is temporarily supplied to the preheating heater 6. The air in the intake system of the diesel engine 1 is effectively preheated. After that, when the key switch 15 is set to the starter position,
The preheated air is taken in and ignited and burned well. In this starter position, both switches 17 and 1 are
8 is turned off, and the generation of large current and power supply to the preheat heater 6 are stopped, and thus the battery power source is also used for the preheat heater 6 of large current specifications.

FIG. 2 is a circuit diagram showing a specific embodiment of the overcurrent detection circuit 27, in which the reference voltage circuit 28 is a positive connection L
_A constant voltage source V _REF is connected to the negative connection L ₂ via two resistors Ra and Rb, and is connected to the positive phase input of the operational amplifier 30 between the resistors Ra and Rb. As the comparison voltage circuit 29, the resistance Rs of the negative connection L ₂ is connected to the negative phase input of the operational amplifier 30. In addition, the resistor R as the power-up circuit 31
constant voltage source V _REF and transistor Q in parallel with a
₁ , the resistor Rd is connected, and the base of the transistor Q ₁ is connected to the resistor Rs via the MOSFET Q ₂ . Then, connect the power-up switch 18 to the gate of MOSFET Q _2, the positive electrode connection L preheating switch 1 to ₁ terminal
7. Preheater 6 is connected.

According to this embodiment, both switches 1 are normally operated.
7,18 is turned off and transistor Q ₁ and MOSFET Q ₂
Is also turned off, and the resistor Rd is de-energized. Therefore, the reference voltage of the positive phase input of the operational amplifier 30 is set by the resistors Ra and Rb, and the reference voltage V _{a1 in} this case is as follows. V _a1 = V _REF · Rb / (Ra + Rb) Further, the comparison voltage V _b is represented by V _b = Rs · I by the resistance Rs and the load current I, and these are shown in FIG. Therefore, the load current I is small, in the case of V _b <V _a1 is in the "I" point of FIG. 3, the comparison voltage V _b with the load current I
Becomes higher than the reference voltage V _a1 , the overcurrent is detected and the operational amplifier 30 limits V _{b to} V _a1, and the load current I in this case becomes the rated output current I _{K1 at the} point “B”.
On the other hand, if both switches 17 and 18 are turned on at low temperature start, M
The OSFET Q ₂ is turned on, the transistor Q ₁ is also turned on, and the resistor Rd is connected in parallel with the resistor Ra to conduct electricity. Therefore, the reference voltage V _a2 in this case has three resistors Ra and R.
b a and Rd, V _a2 = V _REF Rb / (Rx + Rb) Rx = Ra Rd / (Ra + Rd), which is increased and changed as shown in FIG. Therefore, the load current I can be increased more than the rated output current as at the “d” point, and the comparison voltage V _b becomes the high reference voltage V.
_When it becomes _a2 or more, overcurrent is detected, and the load current I is limited to the reference voltage V _a2 and I _K2 by the constant resistance Rs. Incidentally, D
In the C-DC converter 20, for example, six modules 20a are installed, and the total load current I is 6 times as described above, which indicates that the current of the preheat heater 6 is very large. Moreover, since the power-up operation is performed for a short time when the outside temperature is low, the problem such as damage does not occur even if the temperature of the element rises temporarily.

FIG. 4 is a circuit diagram of essential parts showing an embodiment in which a fail-safe function is provided so as to prevent the driver from erroneously performing a power-up operation at the time of unnecessary high-temperature start-up. The thermoswitch 32 is connected in series to the up switch 18. The thermo switch 32 detects water temperature, outside air temperature, case temperature, etc., and is turned on at low temperature and turned off at high temperature.

FIG. 5 shows another embodiment, in which a similar thermoswitch 32 is connected to the input side of the constant voltage source V _REF of the power-up circuit 31. As a result, the thermo switch 32 is turned on to perform a power-up operation only when the temperature is low, and the power-up operation is canceled when the temperature is unnecessarily high irrespective of the driver's operation, and at the same time, the temperature stress of the element does not increase under the condition of poor heat radiation As protected.

Although the embodiments of the present invention have been described above, the power-up circuit is not limited to the embodiments. D
Of course, the C-DC converter can be applied to all uses other than the embodiment.

[0016]

As described above, according to the present invention, the DC-
Since a power-up circuit that outputs a large current larger than the rated output current is added to the DC converter, it can be applied as it is to a load that temporarily requires a large current, and the application is expanded. Since the power-up circuit is configured to increase and change its reference voltage by utilizing a circuit for detecting and protecting overcurrent, the structure is simplified and the degree of freedom in setting the current for power-up operation is large. A fail-safe function can be easily added to the power-up operation by a thermo switch, etc., and the fail-safe function can reliably prevent damage to the element. The one in which the power-up operation is applied to the power supply of the preheater at the low temperature start of the diesel engine as in the embodiment is preferable because the intake preheating can be optimally performed and the temperature stress of the element is reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing the principle of a DC-DC converter of the present invention in a state in which it is applied to a diesel engine with a retarder.

FIG. 2 is a circuit diagram showing a specific example of a reference voltage circuit, a comparison voltage circuit, and a power-up circuit in an overcurrent detection circuit.

FIG. 3 is a diagram showing an operating state at a normal time and a power-up time.

FIG. 4 is a circuit diagram of a main part in which a fail-safe function is added to the power-up operation.

FIG. 5 is a circuit diagram similar to FIG. 4 of another embodiment of the present invention.

[Explanation of symbols]

 20 DC-DC converter 20a Module 21 Switching circuit 22 Power transformer 23 Rectifier circuit 24 Filter circuit 27 Overcurrent detection circuit 28 Reference voltage circuit 29 Comparative voltage circuit 30 Operational amplifier 31 Power-up circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Koike 3-1-1 Hinodai, Hino-shi, Tokyo Hino Factory Hino Plant (72) Inventor Atsumi Obata 3-1-1 Hinodai, Hino-shi, Tokyo Address 1 Hino Motors Ltd. inside Hino factory (72) Inventor Kunitoshi Shimizu 3-1-1 Hinodai, Hino-shi, Tokyo Hino factory inside Hino factory (72) Inventor Shuichi Oi Nitta-cho Nitta-gun Gunma prefecture Large Hayakawa 3 Hayakawa Sawafuji Electric Co., Ltd. Nitta Plant (72) Inventor Hiroshi Fujihashi 4-6-301 Ueno, Taito-ku, Tokyo INTEGRAN Co., Ltd. (72) Kuniharu Ogawa Ueno, Taito-ku, Tokyo 4-6-7-301 INTEGRAN Co., Ltd. (72) Inventor Teiji Kumagai 4-6-7-301 Ueno, Ueno, Taito-ku, Tokyo Integran Co., Ltd.

Claims (4)

[Claims] 1. A means for converting a DC voltage input to a module into a predetermined DC voltage by a switching method, an overcurrent is detected by comparing a reference voltage with a comparison voltage by a load current, and the current is limited to a predetermined rated output current. In the DC-DC converter including the overcurrent detection circuit, a DC-DC converter characterized in that a power-up circuit that changes so as to temporarily increase the reference voltage when necessary is added to the overcurrent detection circuit.
DC converter. 2. The power-up circuit has a transistor and a resistor connected in parallel with one resistor of a reference voltage circuit,
2. The DC-DC converter according to claim 1, wherein the resistance is connected to a resistance of a circuit for a load current via a power transistor which is turned on by an electric signal. 3. The DC-DC converter according to claim 1, wherein switch means for performing power-up operation only under conditions such as low temperature is added to the input side or inside the circuit of the power-up circuit. 4. The input side of the module is connected to a battery in a retarder control device of a diesel engine with retarder, the output side is connected to a preheater of an intake system, and an operation signal is sent to a power-up circuit at a preheat position of a key switch. The DC-DC converter according to claim 1, wherein the circuit is configured to receive the input.