Single-stage PFC debugging experience

1206RGB (single)

Single chip microcomputer STM32L151CCU6

Test - lowercase jpg

Kaixin micro test

Test probe P100-M3

Single-stage PFC debugging experience

PFC is low, debugging method:

1. Secondary de-current (R32) detection resistance is increased.
2. The optocoupler power supply resistor (R27) is increased.
3. The comparator current feedback capacitor (C18) is increased.
4. Full voltage detection (eg, SA7527, pin 3 of L6562) resistor (R13) is reduced.

Low-voltage abnormal noise (beep) at the same time low-voltage current can not achieve full voltage:

1. Adjust the PFC first. If the PFC is normal, adjust it as follows.
2. Increase the full voltage detection resistor (R13) to reduce the capacitance in parallel with the resistor. The capacitor (C8) can be used as 102.
3. Determine if the transformer design is appropriate. Adjust the transformer to reduce the number of secondary turns and increase the duty cycle. (I am now a single-stage PFC to achieve 60w, full voltage input) no-load voltage jitter:

1. Generally caused by insufficient power supply of VCC, the voltage feedback part can be adjusted to increase or decrease the voltage feedback capacitor (C17), and the resistance (this circuit has no resistance) (the constant current adjustment method made by different ICs is different).
2. If the above method does not work, reduce the VCC current limiting resistor (R7) or increase the VCC winding turns. When the light is on, it will work normally after a few flashes or a few times:

1. Generally caused by voltage feedback, reduce the secondary such as 358 voltage feedback compensation capacitor (C17).
2. Reduce the compensation capacitor (C6) of the PWM control chip (eg SA7527, L6562) 1, 2 pin.
3. Add a 104 capacitor at the voltage sampling point, such as a 36v output, the reference point is 2.5v, the positive sampling is 68k, the negative sampling is 5.1k, and a 104 capacitor is connected in parallel with 5.1k. The effect is obvious (the reference circuit is connected in parallel on R26).
4. Increase the no-load voltage. In some cases it works.

Constant current accuracy is not high:

For example, if the number of series beads is reduced, the current will become larger.

1. The current sampling resistor can be reduced.
2. Detect feedback ic Power supply is sufficient.
3. Adjust the resistance and capacitance of the current feedback (some circuit designs only have capacitors. For example: 385+431 can only be used to adjust the capacitor).

For example, the current drops after the power supply temperature rises.

1. Use low temperature drift resistors.
2. Increase the reference point voltage (not recommended, small current can be).
3. PCB wiring is unreasonable, the grounding point of the constant current IC must be at the end of the negative current output, so as to avoid the temperature rise, causing the copper skin resistance to become larger, causing the current to decrease (small current is good, high current 3A or more will be It is clear).

Light flashes:

1. Generally, the PFC is too low, and the PFC is solved first. After the PFC is solved, it will basically be good.
2. Reduce the compensation capacitors of pins 1 and 2 of the PWM control chip (eg SA7527, L6562).

Short circuit protection:

1. The secondary feedback preferably has an independent supply winding, and the supply current limiting resistor of this winding is small. The storage capacitor is large. The winding of the winding and the PWM IC must be wound in the middle (if it is a sandwich winding method, it is best to put the two windings in the middle, which is wrapped in the primary.)
2. Increase the primary current limiting resistor.
3. The primary ic current detection line should be short and bend as little as possible.

Low voltage drop current:

1: The primary current limiting resistor is reduced, the effect is obvious, but the short circuit protection effect is reduced.
2: Increase IC 3 pin to ground, full voltage detection resistor to increase the voltage of 3 feet, but it will reduce the PF value of high voltage, but it can be improved by high voltage compensation. The PF value at high voltage is very simple. Originals.
3: Increase the resistance of IC 1, 2 feet, the effect is general, but the effect is obvious when it is increased to 10k, but it will affect the PF value.
4: Reduce the transformer secondary turns to increase the duty cycle, the effect is very obvious, recommended, but pay attention to control the operating frequency. Too high EMC is hard to do.

Wide range of voltage and current:

For example, the no-load voltage is 36v and the constant current is 1.5A. Some power supplies must be loaded to 34v to enter the constant current mode.

1: Increase the compensation capacitor of the secondary voltage feedback, such as the voltage feedback compensation capacitor of 358.
2: Add a 104 capacitor at the voltage sampling point, such as the output of 36v, the reference point is 2.5v, the positive sampling is 68k, the negative sampling is 5.1k, and a 104 capacitor is connected in parallel with 5.1k. This method is much better than adjusting the 358 feedback compensation capacitor, and it can effectively suppress the flash when starting.

Recently I found another problem:

Filling the current, the R32 is bigger, the constant current effect is very poor.

This is caused by the interference of the current detection line. Since the voltage on this line is very low, it is only 0.2v high, and even low voltage signals such as 0.05v are easily interfered. Therefore, R32 must be placed. The closer to the constant current IC, the better, preferably within 3mm, and the wire must be thick and as short as possible.

The reference circuit diagram is as follows:

The above circuit is not clear, you can see the circuit diagram in the PDF document!