The SG3525 PWM ic description

[Ogu Reginald]

Hi, what will happen to the output frequency, pulse width of the SG3525 IC:
1. If no voltage is applied to pin1 and pin2.
2. If the same voltage is applied to pin1 and pin2.
3. If the voltage at pin1 is greater than the voltage at pin2 (and vice versa).

 

[smijesh]

Hi, what will happen to the output frequency, pulse width of the SG3525 IC:
1. If no voltage is applied to pin1 and pin2.
2. If the same voltage is applied to pin1 and pin2.
3. If the voltage at pin1 is greater than the voltage at pin2 (and vice versa).

1. If no voltage is applied to pin1 and pin2.
Ans: No PWM output.
2. If the same voltage is applied to pin1 and pin2.
Ans: Desired duty cycle.
3. If the voltage at pin1 is greater than the voltage at pin2 (and vice versa).
Ans: .
If the voltage at pin1 is greater than the voltage at pin2
Duty cycle will decrease.
If the voltage at pin2 is greater than the voltage at pin1
Duty cycle will increase.

 

[Ogu Reginald]

Thank you for the answer, I want the output pwm to be constant with duty cycle of 45,
if I connect pin 1 and pin2 together and apply a voltage of 2V to them will I get the desired duty cycle?
If no, please tell me what should be done.
What will happen if I apply a voltage of 2V to pin 2 and connect pin 1 to the ground or vice versa?
What will happen if I apply a voltage of 2V to pin 2 with pin 9 connected to pin 1?

 

[FvM]

You can't set a defined duty cycle except zero and maximum (about 49%) without using feedback for the error amplifier. Or bypass the error amplifier by applying a fixed voltage directly to pin 9.

1:1 feedback pin 9 to pin 1 should work, you'll need about 3V input for 45% duty cycle.

 

[Ogu Reginald]

You can't set a defined duty cycle except zero and maximum (about 49%) without using feedback for the error amplifier. Or bypass the error amplifier by applying a fixed voltage directly to pin 9.

1:1 feedback pin 9 to pin 1 should work, you'll need about 3V input for 45% duty cycle.

So I should leave pin1 and pin2 unconnected, apply a voltage of 3V to pin9?

 

[FvM]

That's an option. The voltage will be loaded by about 100 µA. Or use the error amplifier in feedback configuration.