Abstract:
A digital electric power inverter comprising: a CPU, a PWM driving circuit, a PWM converting circuit, a rectifying circuit, an AC driving circuit, a DC/AC inverting circuit, a plurality of detecting circuits and an alarm circuit, the power inverter is characterized by that: the entire circuitry thereof is designed to be controlled by the CPU that can accurately control these circuits to endue the power inverter with an intact and multi-selection protecting function, thus render the parts thereof to develop their largest effects.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a digital electric power inverter, and especially to a DC to AC power inverter particularly suitable to be used as a protection circuit module structure to protect the elements of the power inverter from being damaged and to be able to provide the actuating power for a machine. 
     2. Description of the Prior Art 
     As shown in FIG. 1, heavy tool machines in the markets consume huge electric power when in actuating, if such a machine is to be actuated, several folds of monetary amount must be paid to purchase an electric power inverter with several folds of functional specification for actuating a small machine. For example, a sand wheel needs 200W for running, while the transient power for actuating is over 1000W; therefore, in using such a machine, an electric power inverter of 1000W must be purchased. The reason is that, a conventional electric power inverter triggers a protecting loop to shut outputting in corresponding to the detecting signal from a detecting loop when the output terminal is given a heavy load, to thereby protect the interior electronic elements; this is because that conventional designing has to trigger a protecting line according to the detecting of the output state to turn off the system to protect the product. 
     And a conventional electric power inverter may render the internal detecting loop thereof to mistake a case for a loading short circuit, in which case, the output terminal thereof is connected with an inductive load or in actuating a load with a larger current; thereby, a protection loop is triggered to shut outputting, to in turn make a machine not work. This is an unsolvable problem and technical bottleneck of the conventional electric power inverter in that it is unable to distinguish a short circuit from an inductive load. 
     In conventional designing, PWM (pulse width modulation) mostly adopts the driving mode of IC outputting; if a relatively inexpensive IC is used, the designing will be more difficult or even the specification must be degraded. For example, when a PWM converting signal has an inadequate duty and makes a larger temperature rising, the frequency must be adjusted down or the IC shall be changed to effectively improve the case. 
     Therefore, the motive of the present invention is to improve the conventional electric power inverters to get rid of the above stated defects, and to provide a digital electric power inverter which sufficiently uses the control character of a CPU (a microcomputer) to similarly provide a load with an output power, but the CPU turns off output in time before the output power makes the elements crumbled, in order that the elements can restore their functions; a short time after restoration, the CPU turns on output again, till it once more turns off before the elements are crumbled. The process is repeated again and again to protect the elements from being damaged, and the actuating power for a machine can be provided; this can take the place of the function of a conventional IC, and can make a large improvement in saving the cost of man work and the fineness of products. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to provide an accurately controlling digital electric power inverter with parts able to develop their largest effects. 
     To achieve the above stated object, the present invention is comprised of a CPU, a PWM driving circuit, a PWM converting circuit, a rectifying circuit, an AC driving circuit, a DC/AC inverting circuit, a plurality of detecting circuits and an alarm circuit. The present invention is characterized by that: the entire circuitry thereof is designed to be controlled by the CPU that can accurately control these circuits to endue the power inverter with an intact and multi-selection protecting function, thus to render the parts thereof to develop their largest effects. 
    
    
     The present invention will be apparent in its construction and other features after reading the detailed description of the preferred embodiment thereof in reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a drawing of a current vs. time coordinate showing that a conventional power inverter is unable to satisfy the requirement of a transient current supply; 
     FIG. 2 is an electric block diagram showing of the present invention; 
     FIG. 3 shows the entire electric circuitry of the present invention; 
     FIG. 4 is an output current curve diagram of the present invention; 
     FIG. 5 is a diagram showing the mode of current output of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring firstly to FIGS. 2 and 3, the present invention is comprised of a current detecting circuit  1 , an overload detecting circuit  2 , a temperature detecting circuit  3 , a CPU  4 , a high voltage detecting circuit  5 , an alarm circuit  6 , a PWM driving circuit  7 , an AC driving circuit  8 , a voltage regulation circuit (5V)  9 , a PWM converting circuit  10 , a rectifying circuit  11 , a DC/AC inverting circuit  12  and a switch  13 . 
     Wherein, the current detecting circuit  1  is connected with one end thereof to the DC/AC inverting circuit  12 , with another end thereof to the CPU  4 , and is comprised of an operation amplifier (OPA) connected with a Zener diode and a plurality of resistances, it is provided for detecting whether an output means a short circuit or a false short circuit; 
     the overload detecting circuit  2  is connected with one end thereof to the DC/AC inverting circuit  12 , with another end thereof to the current detecting circuit  1  and then to the CPU  4 , and is comprised of an operation amplifier (OPA), a plurality of diodes, resistances and capacitors; it is provided for detecting whether it is overloading and whether the input DC voltage is overly high or overly low; 
     the temperature detecting circuit  3  is connected directly to the CPU  4 , and is comprised of an operation amplifier (OPA), a heat sensitive resistance  31  and other resistances; it is provided for detecting whether the temperature of the machine is overly high; 
     the CPU  4  includes a transistor, a plurality of resistances and capacitors, a diode, an operation amplifier (OPA) and an LED  41  composing a microcomputer control loop, and is connected with every detecting circuit to provide signals for an AC driving circuit  8  and a PWM driving circuit  7 ; 
     the high voltage detecting circuit  5  is connected with one end thereof to the rectifying circuit  11 , with another end thereof to the CPU  4 , and is comprised of a plurality of transistors, Zener diodes, resistances, a variable resistance and a plurality of capacitors; it is provided for detecting a high voltage state; 
     the alarm circuit  6  is directly connected with the CPU  4 , and is comprised of a transistor, a plurality of diodes and resistances, and a buzzer  61 ; it is provided for detecting an abnormal state of the circuitry of the power inverter to provide a alarm; 
     the PWM driving circuit  7  is connected with one end thereof to the CPU  4 , with another end thereof to a PWM converting circuit  10 , and is comprised of a plurality of transistors, diodes, resistances and capacitors; it is provided for amplifying and reshaping the output PWM signals of the CPU  4 ; 
     the AC driving circuit  8  is connected with one end thereof to the CPU  4 , with another end thereof to the DC/AC inverting circuit  12 , and is comprised of a plurality of transistors and resistances; it is provided for amplifying the output AC driving signals of the CPU  4 ; 
     the voltage regulation circuit  9  is comprised of a voltage regulation IC  91 , a plurality of diodes and capacitors; it is provided for power supplying for normal operation of the entire circuitry of the power inverter; 
     the PWM converting circuit  10  is connected with one end thereof to the PWM driving circuit  7 , with another end thereof to the rectifying circuit  11 , and is comprised of a plurality of FET power transistors, resistances, capacitors and two transformers  101 ,  102 ; it is directly supplied with electric power in the mode of DC inputting, and is provided for increasing the voltage of the driving signals amplified and reshaped by the PWM driving circuit  7  through the transformers to generate high frequency AC signals; 
     the rectifying circuit  11  is connected with one end thereof to the PWM converting circuit  10 , with another end thereof to the DC/AC inverting circuit  12 , it has a high voltage AC output connecting point, and is comprised of a plurality of diodes capacitors and resistances; it is directly supplied with electric power in the mode of DC inputting, and is provided for rectifying the high frequency AC signals generated by the PWM converting circuit  10  to generate an AC high voltage; 
     the DC/AC inverting circuit  12  is connected to receive a DC input, and is connected with the AC driving circuit  8  and the rectifying circuit  11 , the other end thereof is connected separately with the current detecting circuit  1  and the overload detecting circuit  2 , it further has an AC output connecting point, and is comprised of a plurality of transistors, FET power transistors, diodes, Zener diodes, resistances, capacitors and a heat sensitive resistance; it is provided for converting DC high voltage signals provided by the AC driving circuit  8  into AC high voltage output. 
     Thereby, the CPU  4  controls by cooperation the working of the overload detecting circuit  2 , it turns off output in time before the output power makes the elements crumbled, a short time after restoration, the CPU  4  turns on output again. The process is repeated again and again intermittently to protect the elements from being damaged, and the normal working power for a machine load can be afforded, the larger actuating power for the machine can be provided. And the CPU  4  can clearly distinguish a short circuit from a false short circuit according to whether the current is always the same or is gradually reduced, and makes suitable disposing. 
     And a larger feature of present the invention is that, the CPU  4  is built therein with the above stated working circuits having normal values within their working scopes, in order to actively control and compare the above stated situations of the working circuits to adjust the output PWM signals and AC driving signals of them, in this way, the output PWM signals can be modulated in pursuance of the loading state of working of the loops. 
     The above stated circuitry assembled can make the present invention execute the following actions when the switch  13  is closed to actuate the CPU  4 : 
     1. The CPU  4  renders the PWM driving circuit  7  to generate, amplify and reshape signals, the signals amplified and reshaped are increased in voltage by the transformers  101 ,  102  of the PWM converting circuit  10 , the high frequency AC signals generated after increasing of voltage is rectified by the rectifying circuit  11  to get an AC high voltage. 
     2. The CPU  4  renders the AC driving circuit  8  to generate and amplify signals, the signals amplified renders the DC/AC inverting circuit  12  to convert DC high voltage into AC high voltage to generate an AC output. 
     3. The DC/AC inverting circuit  12  provides a current signal which is sent to the current detecting circuit  1  and the overload detecting circuit  2 ; thereby, the detecting states are respectively sent back to the CPU  4  for analysis and judgment, if they are judged as abnormal, the CPU  4  immediately adjust the PWM driving circuit  7  and the AC driving circuit  8  to protect the elements from being damaged. 
     4. Additionally, the CPU  4  also actively detects all the working circuits, in discovering an abnormal signal, it will send a correcting signal or a protecting signal to the PWM driving circuit  7  and the AC driving circuit  8  in no time to give full play to the protecting function. 
     5. The high voltage detecting circuit  5  detects a high voltage state and send the state back to the CPU  4  which execute suitable modulation for the abnormal potential state to make the power supplying state normal. 
     Referring to FIG. 4, the present invention sufficiently utilize the characteristic of the CPU  4 , thereby, when a machine with the actuating transient power of more than 200W is actuated (such as a sand wheel machine with the actuating transient power of more than 1000W), the present invention nonetheless provides a load with an output power, but the CPU  4  turns off output in time within the tolerated scope of safety before the output power makes the elements crumbled, in order that the elements can restore their functions, a short time after restoration, the CPU  4  turns on output again, till it once more turns off before the elements are crumbled. The process is repeated again and again to protect the elements from being damaged, and the actuating power for a machine can be provided. Therefore, although this is not able to provide all the power to transiently afford the machine requirement, it can gradually supply step by step the required actuating power. In view of this, this mode of operation can provide a 200W electric power inverter for actuating a 200W sand wheel machine, it does not require a 1000W electric power inverter for actuating as is the case of a conventional power inverter. 
     The effective designing makes the present invention intermittently control the gradually increased output to afford the larger power required for actuating in operation, and the CPU  4  can clearly distinguish a short circuit from a false short circuit according to variation of current and makes suitable disposing. 
     More importantly, by the fact that the CPU  4  is installed therein a software, the performance of output can be changed when the software is changed by another one, change can be made in pursuance of the requirement of the working conditions of clients without changing the electronic loops hardware after a machine body has been made, this enlarges its scope of applicability, and can largely reduce the cost induced by changing hardware and the designing work induced by changing specifications, and can thereby increase the scope of applicability. 
     And more, in the present invention, the signal, no matter it is a PWM output signal or an AC output signal, is controlled by the CPU; thereby, the present invention can be small, delicate and inexpensive, and can have the advantage of excellent performance.