Troubleshooting a PWM Circuit Design

In summary, the conversation discusses designing a PWM circuit using a circuit from the internet and a TL494 chip. The requirement is a 20kHz frequency and 15V power. The issue arises when connecting a potentiometer, causing no response. The solution involves removing the pot and making specific connections with transistors. However, limitations are mentioned for controlling certain types of fans.
  • #1
billy fok
40
0
I need to design a pwm circuit, i using the circuit from internet that i attached it..
freq is 20khz which is my requirement and 15v to power up the tl494..
there is no response when i connect potentiometer to it...
waveform is attach

can anyone give me advice?
 

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  • #2
Is an old favorite...
Try removing the pot and typing PIN 3 to PIN 15 (output of op amp to - input). Next, attach one end of the pot to ground and the other to pin 14 (5V reference). Attach the wiper of the pot to pin 16 (+ input of op amp).
This done, the 0-V output of the pot should create 0-5V on the feedback pin 3.

Attach the two output transistors in parallel. The emitters (Pin 9 and Pin 10) tied together and the two collectors (pin 8 and Pin 11) tied together. The transistors will be most active when the wiper of the pot is at 0V, and turned off when the pot reaches 5V.

There are very real and significant limitations when applying this circuit to controlling a fan. For fans with logic level PWM inputs this circuit is well suited. For fans with permanent magnet motors, you will need to take precautions not to damage the transistors during start up (start with a low PWM), and include a freewheeling diode to protect the fan from recirculating currents.

This design is not suitable for driving a brush-less fan as the inputs had capacitors that will damage the 494 and the circuit uses electronic switching which will be uspest by having its power rapidly removed. In such a case a DC-DC converter probably the only option (Add inductor, capacitors, and a freewheeling diode.)
 
  • #3
hi.. thanks for the reply, it mean after i adjust the connection, it will create pulse signals and able to adjust the duty ratio using potentiometer??
 

Related to Troubleshooting a PWM Circuit Design

1. What is a PWM circuit design?

A PWM (Pulse Width Modulation) circuit design is a type of electronic circuit that uses a square wave signal to control the amount of power delivered to a load. It is commonly used to control the speed of motors or the brightness of LEDs.

2. What are the common issues that can occur in a PWM circuit design?

The most common issues in a PWM circuit design include incorrect frequency or duty cycle, faulty components, insufficient power supply, and poor grounding. These can result in inaccurate output or complete failure of the circuit.

3. How do I troubleshoot a PWM circuit design?

To troubleshoot a PWM circuit design, you should first check the frequency and duty cycle of the signal using an oscilloscope. If they are not correct, adjust the values accordingly. Next, check for any faulty components and replace them if necessary. Also, ensure that the power supply is sufficient and the circuit is properly grounded.

4. What is the role of a flyback diode in a PWM circuit design?

A flyback diode, also known as a freewheeling diode, is used in a PWM circuit design to protect the circuit from voltage spikes that occur when the load is switched off. It provides a path for the current to flow back to the power supply, preventing damage to the circuit.

5. Can software be used to troubleshoot a PWM circuit design?

Yes, software such as a circuit simulator can be used to troubleshoot a PWM circuit design. It allows you to simulate the circuit and observe the behavior of the signal and components. However, it is still important to physically test the circuit to ensure accurate results.

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