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High Efficiency DC-DC Isolated Converter

R1 22k

Design Note 43 Issue1 January 2000
High Efficiency DC-DC Isolated Converter
Systems peripheral functions often require separate 3.3V or 5V supplies. This function may require an isolated power supply, as the logic supply cannot sink or source enough current. Isolated DC-DC converters are readily available in the market place, however if there are some spare inverters available in the hardware design then a low cost solution can be configured. The circuit in Figure 1 is a replacement for the MAX253 driver circuit. It uses the same transformer as recommended in the Maxim application circuit (part number 76253 / 55 for 5V-5V isolated conversion, and 76253 / 35 for 3.3V-5V isolated conversion).
R1 22k
R2 10k
C1 150pF
C2 0u1F Q1 FMMT617 D1
L1 47uH Vout Vcc ZHSC750 TR1 + C5 15uF + C6 15uF GND C4 15uF +
2 U1 7404
4 U2 7404
6 U3 7404 R3 3k3
D2 C3 0u1F Q2 FMMT617 9 8 U4 7404 R4 3k3 ZHSC750
Figure 1
Design Note 43 Issue1 January 2000
Figure 2