SG3525 output duty cycle is small

1. The ty cycle of SG3525 is adjusted automatically through output feedback and comparison with the reference pin
the transformer is used to adjust the voltage ratio. The ty cycle is compared by a voltage comparator. It depends on the peripheral circuit to sample and compare the voltage input
SG3525 for comparison. Generally, if you choose about 0.45, the two outputs are about 0.9, so you should leave enough dead time
with an adjustable resistor, one end is connected to pin 16, the middle pin is connected to pin 8, and the other end is grounded. The dead zone can be adjusted in a wide range, but it also has disadvantages, so it should be used with caution.

2. SG3525 is a familiar voltage source PWM chip. Its input is to compare the sampled voltage with a reference voltage. The maximum ty cycle of the output PWM is 50%. However, I don't understand why the front-end sampling voltage is simulated by potentiometer, and I can't see any change of ty cycle. Although the gain of the SG3525 error amplifier is large, the input of the inverting end of the front stage of the amplifier changes by 0.5V. The output of the error amplifier will definitely have a change in the ty cycle after comparing with the triangle wave (for example, the triangle wave with amplitude of 4 will generate PWM wave after 1V is compared with it, and the PWM wave with smaller ty cycle will be generated after 1V becomes 3V). But why can't the SG3525 be observed? I have also seen the solution of Dashen in the forum. I can see the change of the output ty cycle when I input AC at the inverting end, but I still don't understand why DC can't work? What's the point of the problem? Please give me your advice

3. The ty cycle is regulated by the turn ratio of the transformer, not by the peripheral circuit.

I don't seem to be quite right. You can refer to the following information, but it should not be regulated by the peripheral circuit http://wenku..com/view/d9623c2e453610661ed9f444.html

4. I can't answer the specific component. After all, the application circuits are different, but the principle is unchanged, that is, changing the reference voltage of 2 pins (the range is about 0.1-3.3v) can change the ty cycle

5. The transformer is used to adjust the voltage ratio. The ty cycle is compared by a voltage comparator. Is to rely on the peripheral circuit sampling comparison voltage input 3525 for comparison
is that ok?

6. maximal

7. Any slight change of 8-pin input voltage will cause the change of pulse width
this problem can be basically solved by using the reference voltage signal with small ripple and high accuracy.

8.

Pin 5-7 short circuit, adjust pin 6, and the reference design is consistent, but please refer to the specification, add resistance between 5 and 7, do not directly short circuit, 7 pin output add capacitance

CT (pin 5): oscillator timing capacitor access terminal. RT (pin 6): oscillator timing resistor access terminal. Discharge (pin 7): the discharge end of the oscillator is connected with a discharge resistor between the end and pin 5 to form a discharge circuit

SG3525 is a current controlled PWM controller, which adjusts the pulse width according to the feedback current. At the input end of the pulse width comparator, the signal flowing through the output inctance coil is directly compared with the output signal of the error amplifier to adjust the ty cycle so that the peak current of the output inctance changes with the change of the error voltage

extended data:

precautions for PWM control:

1. The service life of carbon brush under PWM control is shorter than that under rated voltage (or fixed voltage)

According to the frequency of use, the carbon brush may wear quickly. The frequency of PWM molation used in DC motor is generally 10 ~ 20kHz

3. Repetitive on-off in PWM control may be close to the frequency of motor parts, which may cause resonance and heating

Special attention should be paid to the use. Under PWM control, when using electrolytic capacitor, the motor may not run at a fixed frequency. Please try to use the motor with varistor

DC motor generally uses carbon brush commutator structure for commutation, and the rotating commutator and carbon brush friction proce sparks at commutator commutation. When the motor is running at low speed, the carbon powder generated by the friction between commutator and carbon brush is accumulated in the slot of commutator, which is easy to cause short circuit and burn the motor and drive board. Please pay full attention

reference source: network-sg3525

reference source: Network ty cycle

reference source: network frequency control

9. The output ty cycle can be changed from 0% to 48% by grounding the input 1 pin and 2 pin of the error amplifier and adjusting the output 9 pin level of the error amplifier. SG3525 output ty cycle does not seem to be 100%, try TL494.

10. Repeat, you are not afraid to seal your account again ~ ~ ~

1: the internal one is the op amp, which is used as the error amplifier; The result of amplification will be output to the following PWM molation circuit through 9 pins, which is the basis for adjusting the ty cycle
2: a set of peripheral feedback network is to improve the output response characteristics, which is very important in switching power supply
3: this group of error amplification should be current loop feedback to limit the output or primary current; The transformer sampled is a current transformer.