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PWM power supply with synchronous rectifier and synchronizing oscillator
| Details |
Inventors: Suzuki, Koji;
Assignee: Canon Kabushiki Kaisha (Tokyo, JP)
Primary Examiner: Stephan; Steven L.
Assistant Examiner: Sterrett; Jeffrey
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
There is disclosed a power supply device having a transformer including primary and secondary windings, for generating in said secondary winding a high voltage output corresponding to power supplied to said primary winding, a first switch for on-off switching power supplied to the primary winding of said transformer, a first signal generator for supplying a switching signal at a first frequency to said first switch, a rectifier for rectifying the high voltage output generated in the secondary winding of said transformer, and controller including a second signal generator for supplying a modulating signal at a second frequency lower than said first frequency, for modulating the output of said rectifier by means of controlling the power supplied to the primary winding of said transformer in accordance with said modulating signal. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, the invention will be described in detail in conjunction with embodiments thereof illustrated in the drawings.
FIG.
1 shows the circuit construction of a power supply device according to the invention, and FIG.
2 shows waveforms of signals appearing in various parts of the circuit of FIG.
1.
Reference numerals 1 and 2 in FIG.
1 designate oscillators for generating pulse voltages.
More specifically, the (L,F) oscillator 1 generates a pulse signal at a frequency of 1,800 Hz and having a duty ratio of 20% (A in FIG.
2), and the (HF) oscillator 2 generates a pulse signal at a frequency of 50 kHz and having a duty ratio of 50% (B in FIG.
2).
The output of the (HF) oscillator 2 is supplied to a modulating circuit 3 for substantially 100% amplitude modulation according to the output signal of the (LF) oscilaltor 1.
The application of a voltage of +Vcc from a low voltage power supply through transistor Q1 to the primary winding of step-up transformer T1 is controlled according to the output signal of the modulating circuit 3.
To the secondary side of step-up transformer T1 is connected a clamping circuit for DC component superimposition, which includes capacitor C1, diode D2 and power supply 5, through discharge resistor R1 and rectifying diode D1.
The output of the clamping circuit is provided from terminal P1.
The connection point between resistor R1 and clamping capacitor C1 can be grounded by switch 4, which may be a relay, an analog switch or the like.
Step-up transformer T1 and rectifying diode D1 are connected to each other in a flyback system as shown.
Switch 4 is turned on in synchronism to the provision of a low level output of oscillator 1, i.
e.
, the turning-off of the transistor Q1 and the step-up transformer T1 as shown in C in FIG.
2.
While transistor Q1 is being driven at 50 kHz, a voltage of V1 is obtained at the cathode of clamping diode D1 and smoothed by clamping capacitor C1.
Thus, the output of switch 4 is as shown in C in FIG
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Fuel Cells 
