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From: N1BUG <paul@n1bug.com>
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Message-ID: <4d214d82-a112-84c7-f9ab-c71941f6689a@n1bug.com>
Date: Thu, 12 Apr 2018 12:42:13 -0400
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Subject: Re: LF: W1VD amp help - more waveforms
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Jay,

When the package arrives I will swap out the caps and the IR2110. If
that doesn't do it I will order a new 74F74 and swap out the
resistors. If all of that fails I don't see anything else I can do.
Realistically at my level of expertise if it doesn't work at that
point I will have reached the end of the road. :-(

The caps I have are KEMET part # R82EC1100Z350J

Here is a link to the datasheet:

https://www.mouser.com/datasheet/2/212/KEM_F3101_R82-1103738.pdf

Paul


On 04/12/2018 11:52 AM, jrusgrove@comcast.net wrote:
> Paul
> 
> The outputs of the 74F74 (measured at the 74F74) should be such that one phase turns off while the 
> other turns on ... essentially on top of each other with no dead zone. These outputs are delayed on 
> their trip to the IR2110 by the 1000 pF caps / 15k resistors. It may be difficult to get a good 
> scope presentation of the delay at the IR2110 inputs ... it's better to look at the output. There 
> should be be no significant delay from input to the output of the IR2110.
> 
> If it's not the caps I have no idea what else it could be! Curious about the part number the caps 
> are that you're using. Anyway, your package with 2 caps and an IR2110 should arrive tomorrow. Maybe 
> these parts will do the trick. I certainly hope so!
> 
> Jay
> 
> 
> ----- Original Message ----- 
> From: "N1BUG" <paul@n1bug.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Thursday, April 12, 2018 10:51 AM
> Subject: Re: LF: W1VD amp help - more waveforms
> 
> 
>> Jay,
>>
>> I agree everything points to a problem in the driver circuit.
>>
>> This morning I set up the scope very carefully, took pictures of the
>> gate waveform with the 2000pf. I then removed the added cap on each
>> side to get back to 1000pf and took pictures of the gate waveform
>> again. Looking at before and after pictures side by side there is
>> *no* difference!
>>
>> I've gone over the driver board several more times and cannot find
>> any construction errors. With the IR2110 in circuit, pin 10 measures
>> 14.55k to ground, pin 12 14.66k to ground. With the IR2110 removed I
>> measure 14.93k and 14.81k respectively.
>>
>> I tried to look at some other things but got hopelessly confused.
>> With the IR2110 removed from the socket... 74F74 output is a square
>> wave +4.2V/+0.2V... at the IR2110 input pins (chip still removed)
>> +2.2V/-2.2V square wave which decays linearly to +1.8/-1.8V on each
>> cycle. I guess it being centered around zero is because I am
>> essentially AC coupled through the 1000pf cap? With one scope probe
>> on the 74F74 pin 2 and the other on the IR2110 pin 12 I see no delay
>> or timing difference whatsoever, just the sloped top and bottom of
>> the square wave. I cannot take pictures because I don't have enough
>> hands.
>>
>> With the IR2110 in the socket... 74F74 output +4V/+0.1V square wave.
>> IR2110 input +3.7V (decaying to +2.7V), -0.6V (decaying to -0.4V)
>> with vertical rise and fall. I still see no delay in rise/fall times
>> between 74F74 pin 2 and and IR2110 pin 12. Should I be seeing a
>> delay or at least some softening of the rise/fall?
>>
>> Still not being satisfied that I was confused enough for one day I
>> looked at both IR2110 inputs. The rise and fall are vertical on both
>> with no delay evident in this test either. When one is rising the
>> other is falling making a single vertical line on the scope. This
>> can't be right, can it? The whole idea is to create a delay between
>> phase transitions at the IR2110 input, isn't it?
>>
>> The only possibilities I can think of are that these capacitors
>> don't work in this circuit or I have a bad chip. But even the latter
>> doesn't seem to explain this.
>>
>> Totally lost...
>> Paul
>>
>>
>>
>> On 04/11/2018 08:50 PM, jrusgrove@comcast.net wrote:
>>> Paul
>>>
>>> I just tried my earlier suggestion of doubling the value of the
>>> 'timing' capacitors to 2000 pF on the amplifier. As expected, the
>>> dead zone between the phases about doubled ... and is
>>> now significantly wider than necessary. I'm having a hard time
>>> understanding how you have no dead zone with 1000 pF caps ... and
>>> adding an additional 1000 pF makes no difference to the
>>> waveform! Believe that if you solve the missing dead zone
>>> issue you'll solve the excessive ringing. Something is amiss in your
>>> driver circuit.
>>>
>>> Jay W1VD