Hello all, I have a question about a circuit I have problems with and looking for help, but it requires some intro to the situation. I will try to keep it short.
I have a broken class D amplifier from the early 00's which I made an attempt to repair.
The problem was narrowed down to a pwm driver board, and further to a faulty IC on the driver board.
The pwm driver in question consists of an error amp, triangular wave generator, and a comparator that does the actual pwm. It's supposed to oscillate at a fixed 100kHz freq.
I replaced the faulty chip with a combination of LM319 dual comparator and TL072 dual opamp.
The driver is back to life but I can't get the desired 100kHz
frequency from the triangular generator, the generator oscillates only at 24kHz.
The generator consists of a comparator (half lm319) and an integrator (half tl072).
Below is a (crude) schematic of the triangular gen in question
The measured voltages in the real circuit is -9v for -9v and +9.4v and for +9v.
I've tried to calculate the output frequency from the values of the components and it should oscillate at freq above 100kHz, but it doesn't. But I'm not very confident in my math.
I also tried to reduce the C1 to 8pf and R1 to 100kOhm, this increased the frequency only to 30kHz.
So what I don't know and can't understand is the other factors that may influence the frequency.
Could it be some parasitic capacitance somewhere or 100kHz is too low frequency for this to play any role?
In other words I'm stuck with this and any suggestions will be much appreciated!
I have a broken class D amplifier from the early 00's which I made an attempt to repair.
The problem was narrowed down to a pwm driver board, and further to a faulty IC on the driver board.
The pwm driver in question consists of an error amp, triangular wave generator, and a comparator that does the actual pwm. It's supposed to oscillate at a fixed 100kHz freq.
I replaced the faulty chip with a combination of LM319 dual comparator and TL072 dual opamp.
The driver is back to life but I can't get the desired 100kHz
frequency from the triangular generator, the generator oscillates only at 24kHz.
The generator consists of a comparator (half lm319) and an integrator (half tl072).
Below is a (crude) schematic of the triangular gen in question
The measured voltages in the real circuit is -9v for -9v and +9.4v and for +9v.
I've tried to calculate the output frequency from the values of the components and it should oscillate at freq above 100kHz, but it doesn't. But I'm not very confident in my math.
I also tried to reduce the C1 to 8pf and R1 to 100kOhm, this increased the frequency only to 30kHz.
So what I don't know and can't understand is the other factors that may influence the frequency.
Could it be some parasitic capacitance somewhere or 100kHz is too low frequency for this to play any role?
In other words I'm stuck with this and any suggestions will be much appreciated!