abe94
Member level 1
I need to generate a fixed frequency and variable duty cycle PWM signal. Normally I would've used a microcontroller , but due to unavoidable circumstances , I have to use the TL494. I did an extensive study of the datasheet , but there are some doubts which need to be cleared. The picture shows the block diagram of the TL494.
![Screenshot - 09132015 - 02:16:41 PM.png Screenshot - 09132015 - 02:16:41 PM.png](https://www.edaboard.com/data/attachments/56/56187-9898fb7a98bb7576bd2a64fe17359004.jpg)
What I've decided to do is to connect the Vref pin to the FEEDBACK pin. According to the datasheet , the Vref pin is a reference voltage source of 5V. I'll put a pot in between the Vref pin and the FEEDBACK pin. That way I can control the voltage input into the FEEDBACK pin from 0 - 5V. If my understanding of PWM generation is correct , the PWM comparator should do its work by comparing the DC signal from feedback and the sawtooth from the oscillator. I have 5 questions.
1. Am I doing this right ? I know the TL494n is supposed to be used as a closed loop system with the feedback coming from the output section of the power supply. I want to re-purpose it as a PWM generator with duty cycle controlled by a pot.
2. What confuses me is what am I supposed to do with the other pins , like the error amplifiers and the DTC . Should I leave them unconnected ? Should I pull them to ground ?
3. I'm using the Vref pin as a voltage source. Is this good practice ? Or should I use a separate 5V source ?
4. I want to get single-ended output from the chip , not push pull. This is kind of a newbie question , but how do I wire up the pins for this mode ?
5. I think instead of FEEDBACK pin , I should use the error amplifiers to provide the control signal to the PWM comparator. Would my original method be alright ? If no , then how can I do that ?
Datasheet : https://www.ti.com/lit/ds/symlink/tl494.pdf
Pin Diagram :
![Screenshot - 09132015 - 02:34:35 PM.png Screenshot - 09132015 - 02:34:35 PM.png](https://www.edaboard.com/data/attachments/56/56188-57211d3560ac7d9c405cda9bbea92a32.jpg)
![Screenshot - 09132015 - 02:16:41 PM.png Screenshot - 09132015 - 02:16:41 PM.png](https://www.edaboard.com/data/attachments/56/56187-9898fb7a98bb7576bd2a64fe17359004.jpg)
What I've decided to do is to connect the Vref pin to the FEEDBACK pin. According to the datasheet , the Vref pin is a reference voltage source of 5V. I'll put a pot in between the Vref pin and the FEEDBACK pin. That way I can control the voltage input into the FEEDBACK pin from 0 - 5V. If my understanding of PWM generation is correct , the PWM comparator should do its work by comparing the DC signal from feedback and the sawtooth from the oscillator. I have 5 questions.
1. Am I doing this right ? I know the TL494n is supposed to be used as a closed loop system with the feedback coming from the output section of the power supply. I want to re-purpose it as a PWM generator with duty cycle controlled by a pot.
2. What confuses me is what am I supposed to do with the other pins , like the error amplifiers and the DTC . Should I leave them unconnected ? Should I pull them to ground ?
3. I'm using the Vref pin as a voltage source. Is this good practice ? Or should I use a separate 5V source ?
4. I want to get single-ended output from the chip , not push pull. This is kind of a newbie question , but how do I wire up the pins for this mode ?
5. I think instead of FEEDBACK pin , I should use the error amplifiers to provide the control signal to the PWM comparator. Would my original method be alright ? If no , then how can I do that ?
Datasheet : https://www.ti.com/lit/ds/symlink/tl494.pdf
Pin Diagram :
![Screenshot - 09132015 - 02:34:35 PM.png Screenshot - 09132015 - 02:34:35 PM.png](https://www.edaboard.com/data/attachments/56/56188-57211d3560ac7d9c405cda9bbea92a32.jpg)