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DC/DC converter
| Details |
Inventors: Sakurai, Tadashi; Kojima, Masahiro;
Assignee: Motorola, Inc. (Schaumburg, IL)
Primary Examiner: Wong; Peter S.
Assistant Examiner:
Attorney, Agent or Firm: Bingham; Michael D.
A first converter which includes a switching element operating on a comparatively lower threshold voltage and generating a first output voltage, a second converter which includes a switching element operating on a threshold voltage higher than that of the first conversion unit and generating a second output voltage higher than the first output voltage, and a level shift circuit which provides the switching signal for activating the switching element of the second converter in accordance with generation of the first output voltage. |
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DETAILED DESCRIPTION It is therefore an object of the present invention, considering the problems in the conventional circuit described above, to obtain a high step-up ratio in a DC/DC converter without lowering the conversion efficiency, even in case the input supply voltage is slow, and to secure a stable and reliable start up function of the converter.
A DC/DC converter embodying the present invention comprises a first DC/DC conversion part or unit which includes a switching element operating at a comparatively low threshold voltage and generating a first output voltage (V.
sub.
1), a second DC/DC conversion part or unit which includes a switching element operating at a threshold voltage higher than that of the first unit and generating a second output voltage (V.
sub.
2), and a level shift circuit which provides a switching signal for activating a switching element of the second DC/DC conversion part in response to generation of the first output voltage.
When a power supply voltage, namely an input voltage, is supplied to a DC/DC converter having such a structure, the switching element of the first DC conversion unit switches in response to a switching signal supplied externally or a switching signal supplied from an oscillator provided within the DC/DC converter.
Thereby, the first DC/DC conversion unit generates a higher output voltage (V.
sub.
1) and supplies it to the level shift circuit.
Thereby, the level shift circuit becomes ready to operate and applies the level-shifted switching signal to the switching element of the second DC/DC conversion unit, causing it to perform switching operations.
Thus, the second DC/DC conversion unit generates, with the operation of the switching element thereof, the second output voltage (V.
sub.
2) higher than the output voltage (V.
sub.
1) of the first DC/DC conversion unit and supplies this second output voltage (V.
sub.
2) to the other circuit, for instance, as an output of the DC/DC converter.
When the second output voltage (V.
sub.
2) exceeds a predetermined value, the level shift circuit provides a level shift operation based on the second output voltage (V
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I/O Systems 
