simple PWM generator...

[server]

Version 4
SHEET 1 940 680
WIRE -304 0 -336 0
WIRE -256 0 -304 0
WIRE 64 0 -80 0
WIRE 336 0 144 0
WIRE -336 32 -336 0
WIRE 192 80 176 80
WIRE 208 80 192 80
WIRE 208 96 208 80
WIRE -80 128 -80 0
WIRE 176 128 -80 128
WIRE 336 128 336 0
WIRE 336 128 256 128
WIRE 400 128 336 128
WIRE 464 128 400 128
WIRE 608 128 544 128
WIRE 784 128 688 128
WIRE 848 128 784 128
WIRE 880 128 848 128
WIRE -336 144 -336 112
WIRE 176 160 128 160
WIRE 288 160 256 160
WIRE -80 176 -80 128
WIRE 784 176 784 128
WIRE 192 208 192 192
WIRE 208 208 208 192
WIRE 208 208 192 208
WIRE 224 208 224 192
WIRE 224 208 208 208
WIRE 288 208 288 160
WIRE 400 208 288 208
WIRE 416 208 400 208
WIRE 192 224 192 208
WIRE -80 272 -80 240
WIRE 784 288 784 240
WIRE 0 320 -80 320
WIRE 128 320 128 160
WIRE 128 320 80 320
WIRE 192 320 128 320
WIRE 336 320 336 128
WIRE 336 320 272 320
WIRE -80 352 -80 320
WIRE -80 464 -80 432
FLAG 192 224 0
FLAG 192 80 +5
FLAG -336 144 0
FLAG -304 0 +5
FLAG -80 464 0
FLAG -80 272 0
FLAG 400 128 PWM+
FLAG 784 288 0
FLAG 848 128 DEMOD
FLAG 400 208 PWM-
SYMBOL Comparators\\\\LT1711 208 144 R0
WINDOW 0 52 -81 Left 2
WINDOW 3 26 -48 Left 2
SYMATTR InstName U1
SYMBOL res 160 -16 R90
WINDOW 0 72 57 VBottom 2
WINDOW 3 77 58 VTop 2
SYMATTR InstName R1
SYMATTR Value 20K
SYMBOL voltage -336 16 R0
WINDOW 0 51 47 Left 2
WINDOW 3 59 79 Left 2
SYMATTR InstName V2
SYMATTR Value 5
SYMBOL voltage -80 336 R0
WINDOW 0 -100 55 Left 2
WINDOW 3 -205 99 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value SINE(2.5 1 1K)
SYMBOL res 288 304 R90
WINDOW 0 74 59 VBottom 2
WINDOW 3 84 57 VTop 2
SYMATTR InstName R2
SYMATTR Value 20K
SYMBOL res 96 304 R90
WINDOW 0 74 56 VBottom 2
WINDOW 3 85 57 VTop 2
SYMATTR InstName R3
SYMATTR Value 1K
SYMBOL cap -96 176 R0
WINDOW 0 57 32 Left 2
WINDOW 3 57 66 Left 2
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL res 560 112 R90
WINDOW 0 77 55 VBottom 2
WINDOW 3 84 55 VTop 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL cap 768 176 R0
WINDOW 0 61 17 Left 2
WINDOW 3 57 51 Left 2
SYMATTR InstName C2
SYMATTR Value 2n
SYMBOL ind 592 144 R270
WINDOW 0 -40 64 VTop 2
WINDOW 3 -49 64 VBottom 2
SYMATTR InstName L1
SYMATTR Value 70m
TEXT -306 304 Left 2 !.tran 2m
TEXT -344 200 Left 2 ;PWM Generator
TEXT -344 248 Left 2 ;JL Nov 4 2020


--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Edward Rawde]

<jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[piglet]

On 05/11/2020 5:46 am, Edward Rawde wrote:

jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

 

[piglet]

On 05/11/2020 10:27 am, piglet wrote:

On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

  Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

 

[legg]

On Thu, 5 Nov 2020 00:46:26 -0500, \"Edward Rawde\"
<invalid@invalid.invalid> wrote:

jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

Perhaps it\'s more relevant to ask how the simulation
manages to generate a DC offset on the outputs, from
the 2.5V ideal of the simulator.

- the source DC level doesn\'t \'measure\' 2.500V, and that
error follows through, with a gain of 20.

Maybe this is a \'real life\' function of LTspice. . .
simulating that nothing is perfect ?

You just don\'t expect to see errors in arbitrary
sources.

RL

 

[server]

On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com>
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

  Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970. Thinking it over, I probably should use something better,
constant-frequency and linear almost to the rails. That will take more
parts, but I may as well use a few more parts to optimize using a
kilowatt power supply and a lot of mosfets and heat sinks and fans.

I\'m going to build an open-loop class-D amplifier so I need good PWM.
A closed-loop amp presents a negative impedance to the power supply,
but open-loop looks positive. That could matter when things get hot.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Thu, 05 Nov 2020 07:25:12 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

  Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970. Thinking it over, I probably should use something better,
constant-frequency and linear almost to the rails. That will take more
parts, but I may as well use a few more parts to optimize using a
kilowatt power supply and a lot of mosfets and heat sinks and fans.

I\'m going to build an open-loop class-D amplifier so I need good PWM.
A closed-loop amp presents a negative impedance to the power supply,
but open-loop looks positive. That could matter when things get hot.

This is mostly brute force, but it is constant-frequency and will go
arbitrarily close to the rails, depending on how RRO the opamp really
is.

Version 4
SHEET 1 1500 724
WIRE -336 16 -368 16
WIRE -288 16 -336 16
WIRE 288 16 -192 16
WIRE 512 16 288 16
WIRE -368 48 -368 16
WIRE 288 64 288 16
WIRE -112 96 -128 96
WIRE -96 96 -112 96
WIRE -96 112 -96 96
WIRE 384 128 368 128
WIRE 400 128 384 128
WIRE -192 144 -192 16
WIRE -128 144 -192 144
WIRE 16 144 -48 144
WIRE 784 144 768 144
WIRE 800 144 784 144
WIRE -368 160 -368 128
WIRE 400 160 400 128
WIRE 800 160 800 144
WIRE -128 176 -192 176
WIRE 96 176 -48 176
WIRE 288 176 288 128
WIRE 288 176 176 176
WIRE 368 176 288 176
WIRE 512 192 512 16
WIRE 512 192 432 192
WIRE 640 192 512 192
WIRE 768 192 640 192
WIRE 928 192 848 192
WIRE 992 192 928 192
WIRE 1088 192 992 192
WIRE 1232 192 1168 192
WIRE 1376 192 1312 192
WIRE 1440 192 1376 192
WIRE 1472 192 1440 192
WIRE 368 208 288 208
WIRE -112 224 -112 208
WIRE -96 224 -96 208
WIRE -96 224 -112 224
WIRE -80 224 -80 208
WIRE -80 224 -96 224
WIRE 768 224 720 224
WIRE 880 224 848 224
WIRE 1376 240 1376 192
WIRE -112 256 -112 224
WIRE 16 256 16 144
WIRE 400 256 400 224
WIRE 784 272 784 256
WIRE 800 272 800 256
WIRE 800 272 784 272
WIRE 816 272 816 256
WIRE 816 272 800 272
WIRE 880 272 880 224
WIRE 992 272 880 272
WIRE 1008 272 992 272
WIRE 784 304 784 272
WIRE 1376 352 1376 304
WIRE -192 384 -192 176
WIRE 16 384 16 336
WIRE 16 384 -192 384
WIRE 96 384 16 384
WIRE 288 384 288 208
WIRE 288 384 176 384
WIRE 544 384 512 384
WIRE 592 384 544 384
WIRE 720 384 720 224
WIRE 720 384 672 384
WIRE 784 384 720 384
WIRE 928 384 928 192
WIRE 928 384 864 384
WIRE 288 416 288 384
WIRE 512 416 512 384
WIRE 288 528 288 496
WIRE 512 528 512 496
FLAG 784 304 0
FLAG 784 144 +5
FLAG -368 160 0
FLAG -336 16 +5
FLAG 512 528 0
FLAG 992 192 PWM+
FLAG 1376 352 0
FLAG 1440 192 DEMOD
FLAG 992 272 PWM-
FLAG 544 384 IN
FLAG 640 192 TRI
FLAG -112 256 0
FLAG -112 96 +5
FLAG 400 256 0
FLAG 384 128 +5
FLAG 288 528 0
SYMBOL Comparators\\\\LT1711 800 208 R0
WINDOW 0 52 -81 Left 2
WINDOW 3 26 -48 Left 2
SYMATTR InstName U1
SYMBOL voltage -368 32 R0
WINDOW 0 51 47 Left 2
WINDOW 3 59 79 Left 2
SYMATTR InstName V2
SYMATTR Value 5
SYMBOL voltage 512 400 R0
WINDOW 0 78 65 Left 2
WINDOW 3 36 101 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value SINE(2.5 2.4 1K)
SYMBOL res 880 368 R90
WINDOW 0 74 59 VBottom 2
WINDOW 3 84 57 VTop 2
SYMATTR InstName R2
SYMATTR Value 1G
SYMBOL res 688 368 R90
WINDOW 0 -46 54 VBottom 2
WINDOW 3 -39 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 1K
SYMBOL res 1184 176 R90
WINDOW 0 77 55 VBottom 2
WINDOW 3 84 55 VTop 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL cap 1360 240 R0
WINDOW 0 61 17 Left 2
WINDOW 3 57 51 Left 2
SYMATTR InstName C2
SYMATTR Value 2n
SYMBOL ind 1216 208 R270
WINDOW 0 -40 64 VTop 2
WINDOW 3 -49 64 VBottom 2
SYMATTR InstName L1
SYMATTR Value 70m
SYMBOL Comparators\\\\LT1711 -96 160 R0
WINDOW 0 68 -92 Left 2
WINDOW 3 40 -56 Left 2
SYMATTR InstName U2
SYMBOL Opamps\\\\UniversalOpamp2 400 192 R0
WINDOW 0 41 -38 Left 2
SYMATTR InstName U3
SYMATTR Value2 Avol=1Meg GBW=20Meg Slew=20Meg
SYMBOL res 192 160 R90
WINDOW 0 75 53 VBottom 2
WINDOW 3 82 52 VTop 2
SYMATTR InstName R1
SYMATTR Value 5K
SYMBOL cap 304 128 R180
WINDOW 0 73 57 Left 2
WINDOW 3 62 26 Left 2
SYMATTR InstName C1
SYMATTR Value 200p
SYMBOL res 32 352 R180
WINDOW 0 57 66 Left 2
WINDOW 3 58 34 Left 2
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL res 192 368 R90
WINDOW 0 72 56 VBottom 2
WINDOW 3 83 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 20K
SYMBOL voltage 288 400 R0
WINDOW 0 61 43 Left 2
WINDOW 3 59 79 Left 2
SYMATTR InstName V1
SYMATTR Value 2.5
TEXT 1072 472 Left 2 !.tran 2m uic
TEXT 1040 360 Left 2 ;PWM Generator 2
TEXT 1056 408 Left 2 ;JL Nov 5 2020




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Edward Rawde]

<jlarkin@highlandsniptechnology.com> wrote in message
news:fq58qfd3d1vqkdq3hug8vu5drqafbok14m@4ax.com...

On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970.

You would have published it at the time then?
Reminds me of other things which became standards such as baxandall tone
control and tobey-dinsdale audio amplifier.
Such things would likely be hidden behind patents now.

Thinking it over, I probably should use something better,
constant-frequency and linear almost to the rails. That will take more
parts, but I may as well use a few more parts to optimize using a
kilowatt power supply and a lot of mosfets and heat sinks and fans.

I\'m going to build an open-loop class-D amplifier so I need good PWM.
A closed-loop amp presents a negative impedance to the power supply,
but open-loop looks positive. That could matter when things get hot.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[John Larkin]

On Thu, 5 Nov 2020 12:53:52 -0500, \"Edward Rawde\"
<invalid@invalid.invalid> wrote:

jlarkin@highlandsniptechnology.com> wrote in message
news:fq58qfd3d1vqkdq3hug8vu5drqafbok14m@4ax.com...
On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970.

You would have published it at the time then?

Certainly not. I design stuff to sell.

 

[John Larkin]

On Thu, 05 Nov 2020 09:53:45 -0500, legg <legg@nospam.magma.ca> wrote:

On Thu, 5 Nov 2020 00:46:26 -0500, \"Edward Rawde\"
invalid@invalid.invalid> wrote:

jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard


Perhaps it\'s more relevant to ask how the simulation
manages to generate a DC offset on the outputs, from
the 2.5V ideal of the simulator.

I noticed that but haven\'t investigated. Could be time delays or
something. More likely comparator bias current, which can get weird.

I\'m going to drive a transformer from a full bridge switcher, so I\'ll
probably include some slow DC feedback to keep the differential output
close to zero, so a little offset won\'t matter.

- the source DC level doesn\'t \'measure\' 2.500V, and that
error follows through, with a gain of 20.

Maybe this is a \'real life\' function of LTspice. . .
simulating that nothing is perfect ?

You just don\'t expect to see errors in arbitrary
sources.

RL

 

[Lasse Langwadt Christensen]

torsdag den 5. november 2020 kl. 16.25.22 UTC+1 skrev jla...@highlandsniptechnology.com:

On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

  Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970. Thinking it over, I probably should use something better,
constant-frequency and linear almost to the rails. That will take more
parts, but I may as well use a few more parts to optimize using a
kilowatt power supply and a lot of mosfets and heat sinks and fans.

I\'m going to build an open-loop class-D amplifier so I need good PWM.
A closed-loop amp presents a negative impedance to the power supply,
but open-loop looks positive. That could matter when things get hot.

use an MCU with few ADCs and timers it can do everything you want plus all
the nice \"don\'t catch fire\" features

you can even get an MCU with the gate drivers and a few opamp/comparators
in a single package

 

[John Larkin]

On Thu, 5 Nov 2020 12:26:27 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

torsdag den 5. november 2020 kl. 16.25.22 UTC+1 skrev jla...@highlandsniptechnology.com:
On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

  Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970. Thinking it over, I probably should use something better,
constant-frequency and linear almost to the rails. That will take more
parts, but I may as well use a few more parts to optimize using a
kilowatt power supply and a lot of mosfets and heat sinks and fans.

I\'m going to build an open-loop class-D amplifier so I need good PWM.
A closed-loop amp presents a negative impedance to the power supply,
but open-loop looks positive. That could matter when things get hot.



use an MCU with few ADCs and timers it can do everything you want plus all
the nice \"don\'t catch fire\" features

you can even get an MCU with the gate drivers and a few opamp/comparators
in a single package

My box is all done, and I want to beef up the power amp boards, so
going all analog is sensible. Doesn\'t need code!

The existing board has a current shunt and an isolated delta-sigma ADC
that goes into our FPGA, so we could do some shutdowns or current
limiting there.

The existing TI Class-D amp chip has too many fault sensing/shutdown
features. We want to be able to really blast out power until the
transformer smokes. Its thermal time constant seems to be about 30
minutes, so we could slam it for one.

Big fets! Dumb circuits!

 

[Lasse Langwadt Christensen]

fredag den 6. november 2020 kl. 00.05.52 UTC+1 skrev John Larkin:

On Thu, 5 Nov 2020 12:26:27 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

torsdag den 5. november 2020 kl. 16.25.22 UTC+1 skrev jla...@highlandsniptechnology.com:
On Thu, 5 Nov 2020 13:49:33 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 05/11/2020 10:27 am, piglet wrote:
On 05/11/2020 5:46 am, Edward Rawde wrote:
jlarkin@highlandsniptechnology.com> wrote in message
news:5996qf5sdjd0gnup5ipsce8ijgo60f2vef@4ax.com...

I\'ve used something similar in the past.
https://www.google.com/search?q=comparator+PWM+generator&tbm=isch

--

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

  Claude Bernard




Yes, this is a well known circuit. I have used this topology since mid
1970s and have been posting PWM modulators using this on SED over the
years (most recently for a lamp slow fade-up). If one can tolerate the
frequency variation it is a wonderful low-cost solution. Wonder what is
special about OPs?

piglet

I think I can now answer my own question. It is not the OP PWM generator
that is special but instead it is the demodulator. JL has picked RLC
values that give good ripple and phase shift.

piglet

That\'s just a simulation demo, to see the recovered sine wave and the
PWM distortion. It\'s a Bessel lowpass.

Actually I invented this PWM circuit (as I\'m sure others have) ca
1970. Thinking it over, I probably should use something better,
constant-frequency and linear almost to the rails. That will take more
parts, but I may as well use a few more parts to optimize using a
kilowatt power supply and a lot of mosfets and heat sinks and fans.

I\'m going to build an open-loop class-D amplifier so I need good PWM.
A closed-loop amp presents a negative impedance to the power supply,
but open-loop looks positive. That could matter when things get hot.



use an MCU with few ADCs and timers it can do everything you want plus all
the nice \"don\'t catch fire\" features

you can even get an MCU with the gate drivers and a few opamp/comparators
in a single package

My box is all done, and I want to beef up the power amp boards, so
going all analog is sensible. Doesn\'t need code!

The existing board has a current shunt and an isolated delta-sigma ADC
that goes into our FPGA, so we could do some shutdowns or current
limiting there.

The existing TI Class-D amp chip has too many fault sensing/shutdown
features. We want to be able to really blast out power until the
transformer smokes. Its thermal time constant seems to be about 30
minutes, so we could slam it for one.

Big fets! Dumb circuits!

if you already have an FPGA just use that, all you need is a couple of pins