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I am trying to implement a brushless motor driver using an IR2301S driver. I started with testing the driver without MOSFETs. Here is schematic:

enter image description here

In the datasheet of the IR2301S is this picture:

enter image description here If I understood correctly, I should see oscillating on LO if there is an oscillating signal on LIN and unconnected HIN, VS. I got it. But when I send an oscillating signal on HIN while LIN and VS are unconnected I don't see oscillating on HO; there is stable 6 V on HO. Input signal amplitude is 3.3 V. I've tried to change VCC up to 12 V, change the capacity of C1 and C4 from 1 μF to 100 μF without luck. What am I doing wrong?

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    \$\begingroup\$ That's a floating high-side driver. As Andy shows in his answer, if you just leave Vs floating you'll never see any output on Ho. \$\endgroup\$
    – brhans
    Commented May 21, 2015 at 14:06
  • \$\begingroup\$ The high side portion of the circuitry in the driver IC is powered by the charge stored in the capacitor C2. In normal operation, where the gate driver controls a MOSFET half bridge, turning the low side transistor on pulls VS low, charging C2 through the diode D1. If you keep the low side transistor off for an extended time, the voltage at VS is likely higher than VCC, causing C2 to slowly discharge and the high side to turn off, even when HIN is high. \$\endgroup\$
    – jms
    Commented May 21, 2015 at 20:33

1 Answer 1

Reset to default
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Here is the block diagram: -

enter image description here

Without connecting Vs to 0V and Vb to +V you will see nothing on HO

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