H-Bridge Driving Circuit Help using IR2181
H-Bridge Driving Circuit Help using IR2181
(OP)
I have designed the attached H-Bridge circuit, but I am having trouble using an IR2181 High/Low Side driver for driving the FETs. Even with nothing on the High-Input of the IR2181, the device is outputting on the high-output and I cannot determine why. Does anyone have any experience with the IR2181's? Any suggestions for troubleshooting?
EE Intern
Stevens Institute of Technology





RE: H-Bridge Driving Circuit Help using IR2181
RE: H-Bridge Driving Circuit Help using IR2181
EE Intern
Stevens Institute of Technology
RE: H-Bridge Driving Circuit Help using IR2181
In my world nothing ain't nothing. A floating input is often a high.
RE: H-Bridge Driving Circuit Help using IR2181
TTFN
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RE: H-Bridge Driving Circuit Help using IR2181
TTFN
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RE: H-Bridge Driving Circuit Help using IR2181
EE Intern
Stevens Institute of Technology
RE: H-Bridge Driving Circuit Help using IR2181
The FETs, Q1 and Q2, as well as Q3 and Q4, are FQB55N10. (http://pdf.zener.ru/90581.pdf?datasheet%20Fairchil...)
Something else I have noticed is that Vs is sitting at about 11V. Not sure if this is normal for this device.
EE Intern
Stevens Institute of Technology
RE: H-Bridge Driving Circuit Help using IR2181
TTFN
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RE: H-Bridge Driving Circuit Help using IR2181
RE: H-Bridge Driving Circuit Help using IR2181
OperaHouse, I agree with you. I found that the low-side FET needs to be turned on in order for the high-side output of the same driver to be turned off. So, for example, if Q3 is PWM'd Q1 will no longer be driven high, and the bridge will act as it is supposed to. The issue that caused me concern was that I was not using the circuit in it's full implementation when I started measuring voltages.
Thanks for the help guys.
EE Intern
Stevens Institute of Technology
RE: H-Bridge Driving Circuit Help using IR2181
Second - Watch your layout around half-bridge drivers. Check the IR website - they have app notes for layout of half bridge drivers. This becomes especially true the faster you switch these circuits. You're not indicating it on your schematic but you need a ceramic capacitor bypass from your +20V very near your diode to ground. I always make sure this capacitor is at least 2x to 5x the boost capacitor value.
RE: H-Bridge Driving Circuit Help using IR2181
C7 and C8 are basically the power supplies for the high side driver circuit. You have to turn-on transistors Q3 and Q4 to charge C7 and C8 before the high side driver will even work. Then, you have to be switching Q3 and Q4 on every x seconds to keep the capacitors C7 and C8 charged so the high side driver will keep working. I can't tell you the number x but how to calculate it or pick the capacitor sizes for C7 and C8 based on your switching duty is in the IR data.
You have to measure the high side output between H0 and Vs. Measuring from H0 or Vs to COM means nothing.
And of course Vs will be around 11V when you first power up the circuit. Basically, it will be a little less than the power supply voltage until you start operating the circuit. The transistors are off so C7 and C8 are not charged and the high side driver places some load across C7 and C8, which keeps the capacitors discharged. So, you have 12V applied to D8 and D9 which passes through the diodes with the diode voltage drop before reaching Vb and then it passes through the IC load before reaching Vs.
RE: H-Bridge Driving Circuit Help using IR2181
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