西里古1992

maychang published on 2019-1-9 10:50 Similar switching power supply control chips (including power tubes) include MC34063 and others. These chips are all turned off when the output voltage is high enough to a certain value, and turned off when the output voltage is low enough to a certain value...

Where is the performance slightly worse? Is the output voltage ripple large? Is it unstable?

maychang

Sirigu1992 posted on 2019-1-9 11:02 Where is the performance slightly worse? Is the output voltage ripple large? Is it unstable?

Where is the performance slightly worse? Is the output voltage ripple large? Is it unstable? The ripple is also large, and the output voltage is not stable enough.

西里古1992

maychang published on 2019-1-9 09:09 The pulse frequency of this chip is not fixed, so it is hard to say that it is PWM (pulse width modulation), but the duty cycle of each pulse does change with the output voltage. ...

So it is based on the FB voltage and the 2.55V reference voltage to determine whether the Mos is turned on or off. Vcc is used to power the chip. What is the internal high-voltage regulator mentioned in the figure? When it reaches VCCoff, the IC starts switching. Does it mean that the rectification chip will work at this time? Then it is said that it turns on the external VCC capacitor when the VCC voltage falls below VCCON,is the external VCC capacitor C2? I am confused by this.

maychang

Sirigu1992 posted on 2019-1-9 12:00 So it is based on the FB voltage and the 2.55V reference voltage to determine whether the Mos is turned on or off. Vcc is used to power the chip. The figure mentions internal...

What is the internal high-voltage regulator mentioned in the figure? I guess it is a linear regulator with an input of hundreds of volts and an output of around 5V. This linear regulator has very high losses, so it can only be used once at each startup and cannot be used continuously.

maychang

Sirigu1992 posted on 2019-1-9 12:00 So it is based on the FB voltage and the 2.55V reference voltage to determine whether the Mos is turned on or off. Vcc is used to power the chip. The figure mentions internal...

"Does the external VCC capacitor refer to C2?" I guess the external VCC capacitor is C2 in the 150th floor figure.

传媒学子

Yes, the electrolytic capacitor at the front is responsible for filtering out large fluctuations, while the π-type filter at the back is responsible for filtering out the high-frequency clutter components in the waveform, making the output flatter.

西里古1992

maychang posted on 2019-1-9 12:05 What is the internal high-voltage regulator mentioned in the picture? I guess it is a linear regulator with an input of hundreds of volts and an output of...

The function of this regulator is to power on and stabilize the voltage between VCC and SOURCE at around 5V.

maychang

Sirigu1992 posted on 2019-1-9 12:45 The function of this voltage regulator is to power on and stabilize the working voltage between VCC and SOURCE at around 5V

"The function of this voltage regulator is to power on and stabilize the working voltage between VCC and SOURCE at around 5V" It is estimated that it is mainly used to charge C2 in the 150th floor picture. After C2 is charged, it can be used by the chip for several switching cycles.

西里古1992

maychang posted on 2019-1-9 12:47 "The function of this voltage regulator is to power on and stabilize the working voltage between VCC and SOURCE at about 5V." It is estimated that it is mainly for C2 in the 150th floor picture...

Teacher, is the efficiency of this power supply circuit not high? There is no efficiency value in the specification book. I want to select the L1 filter inductor of the 150th floor. The rated current value requires the input current. The output current is about 300mA. I don’t know how to calculate the input current without the efficiency value.

maychang

Sirigu1992 posted on 2019-1-10 19:09 Teacher, is this power supply circuit inefficient? There is no efficiency value in the specification. I want to select the L1 filter inductor on the 150th floor. The rated current value...

Do you really plan to use this chip? This is a Buck circuit. When the inductor current of the Buck circuit is continuous, the ratio of the output voltage to the input voltage is roughly the ratio of the power tube on time to the off time. The input voltage is the voltage after 220V AC rectification and filtering, which is about 300V, and the output is about 12V. It can be seen that the ratio of the off time to the on time. The input voltage of this chip is very high and the output voltage is quite low, so the on time is very short and the off time is quite long. During the power tube shutdown period, the inductor provides energy to the load. The efficiency is mainly determined by the power tube voltage drop, rising edge loss, falling edge loss, freewheeling tube voltage drop, inductor loss, etc. in the chip. The efficiency is closely related to the load current, so it is difficult to give an accurate value in the manual.

maychang

Sirigu1992 posted on 2019-1-10 19:09 Teacher, is this power supply circuit inefficient? There is no efficiency value in the specification. I want to select the L1 filter inductor on the 150th floor. The rated current value...

The current in this inductor does not change much. Under continuous current conditions, the maximum current in the inductor will not exceed twice the DC output current (exactly twice when the current is critical). It is recommended not to use this chip. It is best to use a flyback topology, consider using UC3842~3845 chips, and discrete power transistors. The transformer size of the flyback circuit is only slightly larger than the inductor in the circuit you plan to use, less than twice. But the performance of the flyback is much better and it is also easy to design and manufacture.

西里古1992

maychang posted on 2019-1-10 19:35 The current in the inductor does not change much. Under the condition of continuous current, the maximum current in the inductor will not exceed twice the DC output current (the current is exactly two times when it is critical...

Is that UC3842 a pulse width modulator? Is it the flyback topology of Figure 1? Should the Tinyswitch3 in Figure 2 be replaced with UC3842? Mainly because I have never been exposed to flyback power supply, I have no experience in transformer selection and design, and I am not familiar with core calculation. I am afraid that it will take a long time to make it.

maychang

Sirigu1992 posted on 2019-1-10 19:59 Is that UC3842 a pulse width modulator? Is it the flyback topology shown in Figure 1? Should I replace the Tinyswitch3 in Figure 2 with UC3842? Mainly, I have never...

"Is that UC3842 a pulse width modulator? Is it the flyback topology shown in Figure 1?" UC3842~3845 is a pulse width modulation chip, which is the flyback topology shown in Figure 1.

maychang

Sirigu1992 posted on 2019-1-10 19:59 Is that UC3842 a pulse width modulator? Is it the flyback topology in Figure 1? Should we replace the Tinyswitch3 in Figure 2 with UC3842? Mainly, there is no...

"Should we replace the Tinyswitch3 in Figure 2 with UC3842?" No. The Tiny Switch chip in Figure 2 has the power tube built into the chip, while UC3842~3845 must be connected to an external power tube.

西里古1992

maychang posted on 2019-1-7 16:14 143th floor The voltage waveform across the diode is correct. It can be seen from the electrical schematic diagram D5 in the MP173 manual that the voltage across the two ends when the power MOS tube inside the MP173 is turned on is...

Teacher, in this circuit, when the tube is turned on, the voltage at the left end of L2 is 300V, and the voltage at the right end is 12V. Can I say that?

maychang

Sirigu1992 posted on 2019-1-24 10:43 Teacher, in this circuit, when the tube is turned on, the voltage at the left end of L2 is always strong 300V, and the right end is weak 12V. Can we say that?

In this circuit, when the tube is turned on, the voltage at the left end of L2 is always strong 300V, and the right end is weak 12V. Can we say that? If you want, you can say that.

syw272

After reading this post, I supplemented and corrected some of my own knowledge, which is equivalent to relearning. Thank you!