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> Amplifier
and Comparator Circuits > APP 529
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App notes
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> APP 529
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App notes
> Power-Supply
Circuits > APP 529

Nov 01, 2000

Keywords: step-up controller, input converter,
transformer flyback, flyback converter
Related
parts

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APPLICATION NOTE 529

15V Input Converter Generates -185V at 50mA

Abstract: This
design note shows how a 15V input flyback converter generates
-185V at 50mA. The circuit uses the MAX668 step-up controller
and a transformer to make a flyback converter.

Additional
information:

Data sheet for
the MAX668

Data sheet for
the MAX4130

Technical
support: power

Figure
1. This circuit uses the MAX668 and a transformer (which will
need about a one-to-six turns ratio) to make a flyback
converter. The op amp inverts the feedback from the negative
output voltage.

The circuit above generates -185V
at 50mA from a +15V input. Based on a MAX668 transformer
flyback application, the circuit employs a custom transformer
to generate -185V through a combination of turns ratio and
duty cycle. The transformer is designed on an SG5-size bobbin
to facilitate the winding and to decrease the leakage
inductance.

D2 is chosen as a fast-recovery diode
to moderate the cost for a high-breakdown voltage part.
Because the diode will see 185V + (6 × VIN) +
flyback due to leakage inductance, a 600V rating is necessary.
C3 is chosen as a film capacitor to get high voltage rating
and high ripple-current capacity. A secondary LC (L1 and C8)
reduces output ripple from 100mVP-P to less than
5mVP-P.

Related parts

MAX4130

Single/Dual/Quad,
Wide-Bandwidth, Low-Power, Single-Supply
Rail-to-Rail I/O Op Amps

Free
samples

MAX668

1.8V to 28V Input, PWM
Step-Up Controllers in µMAX

Free
samples

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Download,
PDF format (71kB)
APP 529: Nov 01, 2000

AN529, AN 529, APP529,
Appnote529, Appnote 529

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