Rainbow Electronics LM27 - Manual (Page 7)

Typical Applications
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Note: The fan’s control pin has internal pull-up. The 10k pull-down sets a slow fan speed. When the output of the LM27 goes low, the fan will speed up.
FIGURE 4. Two Speed Fan Speed Control
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FIGURE 5. Fan High Side Drive
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FIGURE 6. Fan Low Side Drive
LM27
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