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Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
Has anyone ever encountered a similar problem:
When using a pair of TC4421 or TC4422 in a 'push/pull' configuration (i.e. the output taken between the output of each ic), the output wave form is fairly square, but has a sine wave of about 4 times the frequency and about 2 volts superimposed ontop, so the tops of the square wave are 'wavy' like a steady sort of ripple, yet when looking at the output of either chip with respect to ground, the output is a perfect square wave (with a tiny bit of ringing).
I've tried pairs of both types (both invering tc4421 or non inverting tc4422) and pairs of each type (one inverting one noninverting), tried swapping the ics, rebuilding the driver circuit, etc, but i even get the same result driving just from a signal generator. And all this is without any load connected, just directly scopeing the output of each ic. So why does this happen?
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Make sure you have a 0.1uF ceramic cap, and a 10uF electrolytic connected in parallel across the power rails right at each TX442x chip. This is important otherwise the switching action of the chip can cause ringing in the supply wiring to the chip.
Also check your scope probes are correctly compensated and that you are grounding both probes correctly during the differential measurement. The correct way to measure the voltage wavefor _BETWEEN_ the outputs of two chips is to monitor each output with a seprate probe that is grounded to 0v. Then set the scope to display Y1-Y2. Connecting the ground clip of the scope probe to either of the chip's outputs is going to short it to ground.
Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
thanks richie! i wasnt measuring it properly, i was just using one probe, with the ground connected to one output, i thought this would be okay, as the whole driver circuit is floating and i thought the osciloscope is mains grounded? anyway problem solved,
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TC44xx Drivers
