IR2104 high / low side driver

[Pastor Del]

I am troubleshooting an proven circuit (reference attached document). HO is like a full wave rectified signal instead of the half wave expected. My circuit is identical to the typical connection shown on the data sheet for IR2140 so I included that image in the attached document. Vcc is 13.5V, IN is a good square wave & SD it tied to 5V. Replacing the IC did not fix the problem. (Both FETs have also been replaced) Can someone give me some insight to what could cause this problem?

 

[ChrisP58]

I am troubleshooting an proven circuit (reference attached document). HO is like a full wave rectified signal instead of the half wave expected. My circuit is identical to the typical connection shown on the data sheet for IR2140 so I included that image in the attached document. Vcc is 13.5V, IN is a good square wave & SD it tied to 5V. Replacing the IC did not fix the problem. (Both FETs have also been replaced) Can someone give me some insight to what could cause this problem?

There is no rectification going on in the chip. The timing of waveform you get out of pin 7, should look just like the waveform you are putting into pin 2. One pulse in should produce one pulse out. It will just be level shifted up to drive the gate of your high side mosfet.

 

[jpanhalt]

1) What is your signal source? Does it have a common ground with the circuit?
2) What are your 'scope settings? What are the amplitudes of input and output waves? Is the 'scope set for DC coupling or AC?

John

 

[Pastor Del]

Thanks for you replies

Chris: I understand that there is no rectification going on. I was simply using the terms to describe the signal on pin 7

jpanhalt: The signal source is from a processor through an inverting schmitt trigger (5V 60Hz at pin 2) and is a common ground with the circuit. Pin 7 is about 170V. The scope is set to 10mS with DC coupling.

Just found that my IR2104 has only 18 ohms between pins 6 & 7. It has definitely been replace & it's not the FET (I can isolate it with the 10 ohm resistor on the FET gate). I guess this makes this string mute - I'll have to figure out what is taking out my IC. Thanks for you willingness to help.

 

[ronsimpson]

The signal source is from a processor through an inverting schmitt trigger (5V 60Hz at pin 2)

The IR2104 was never intended to run at 60hz. Yes for 60khz.
The capacitor from Vb to Vs is a 'battery' that supplies power to the high side driver. When Vs is high (the top FET is on and the bottom FET is off) the high side driver must live from the power stored in this capacitor.
When Vs is low (the bottom FET is on) power flows through the diode and charges the capacitor to Vcc-0.7 volts.

I do know know what value of capacitor should be used at 60hz. The high side driver will draw 30 to 50uA plus the energy to turn on/off the FET. I would use a capacitor 1000x that used at 60khz.

This idea that you can run the IR2104 slow (60hz) or turn on the top FET 100% of the time is common if you have never used it. I can't find the application note about how to choose the value of capacitor verses top FET on time. There are several versions of this part and I think the information may be in another data sheet.

 

[ChrisP58]

Just found that my IR2104 has only 18 ohms between pins 6 & 7. It has definitely been replace & it's not the FET (I can isolate it with the 10 ohm resistor on the FET gate). I guess this makes this string mute - I'll have to figure out what is taking out my IC. Thanks for you willingness to help.

How did you measure the 18 ohms, and under what conditions? If it was with an ohm-meter, what was the polarity of the probes?

It will be easier to help you, if you post your whole circuit.

 

[Pastor Del]

Sorry for the slow response. Unfortunately, the actual circuit is part of a proprietary circuit that belongs to one of my customers and requires a non-disclosure agreement.

Thanks again for your input. Hope to be able to draw on the knowledge/experience of this forum in the future.