MOS tube anti-reverse connection

SHU_2017

MOS tube anti-reverse connection [Copy link]

 

Recently, I have been learning about the MOS tube anti-reverse connection circuit, and I have been confused by several questions. I would like to ask you for help. 1. Why do we sometimes use two resistors plus a voltage regulator to divide the voltage and protect the GS from breakdown, but sometimes we only use one voltage regulator plus resistors. Is it to reduce the current flowing through the voltage regulator and protect the voltage regulator from burning out? 2. In Figure 1, R3 and C1 are added to absorb spikes and discharge quickly, but they also have a delay effect, which will increase the energy loss of the MOS tube when it is switched on and off, and increase the heat generation. So is this circuit only suitable for low-frequency circuits? 3. What is the function of the inductor L1 at the back end of the MOS tube in Figure 2? Is it to reduce the ripple current?

lingking

The first picture is really of poor quality, without any parameters, and the PMOS is not drawn correctly. In fact, the anti-reverse connection circuit can be just like the second picture, or even simplified a little bit and remove the voltage regulator.

lingking

I think the voltage regulator is used to protect the GS voltage of the MOS tube from exceeding a certain value. When the input voltage increases, the voltage regulator begins to stabilize the voltage. When the input voltage increases within a certain range, the voltage between G and S is kept constant by the voltage regulator, which means that the conduction degree of the MOS remains unchanged, which plays a role in protecting the subsequent circuits.

spaqxc

The voltage regulator reduces voltage fluctuations.

btty038

The minimum voltage control opens and closes the pinch-off, which only requires a certain G voltage, so the opening and closing voltages can be controlled.

SHU_2017

Thank you for your answers, but the first question I want to ask is why sometimes two resistors are used to divide the voltage, and sometimes a resistor and a voltage regulator are used to divide the voltage

仙猫

SHU_2017 posted on 2019-1-23 08:39 Thank you for your answers, but the first question I want to ask is why sometimes two resistors are used for voltage division, and sometimes a resistor and a voltage regulator are used for voltage division: C ...

Depending on the input voltage value, sometimes it is necessary to pay attention not to exceed the maximum withstand voltage between the GS of the tube, so a resistor is used for voltage division. But if the input voltage value is uncertain (or allowed to vary within a certain range), using a voltage regulator tube can adapt to a larger working range.

qwqwqw2088

SHU_2017 posted on 2019-1-23 08:39 Thank you for your answers, but the first question I want to ask is why sometimes two resistors are used to divide the voltage, and sometimes a resistor and a voltage regulator are used to divide the voltage: C ...

"The first question is why sometimes two resistors are used to divide the voltage, and sometimes a resistor and a voltage regulator are used to divide the voltage" According to the conduction voltage requirements of the MOS tube G pole, ensure that it is turned on within the regulated voltage.

bigbat

The first figure: C1 and R3 are "integral circuits", which are mainly used to generate "integral pulses". R1 and R2 are typical voltage divider circuits, which mainly provide G-level voltage. Working principle: First look at the circuit, the left end is the input, and the right end is the output. When the voltage appears, the integral circuit composed of C1 and R3 is turned on, so R3-C1-R1-R2 is a loop, so there will be voltage at the G end! VM1 will be turned on, and "defecation" will be normal! ! ! After it is connected, there will be no "urination" and C1-R3 will have nothing to do. "Input power off" will be fine. Why does R1-R2 divide the voltage? Think about it yourself! It seems that there is no "anti-reverse" here. There is no loop if it is connected incorrectly. The second figure: This is a typical motor drive H-bridge. Don't understand the anti-reverse connection? I can't see what is "related" to this.

PowerAnts

lingking posted on 2019-1-22 22:13 The first picture is really too low quality, there is no parameter, and the PMOS is not drawn correctly. In fact, the anti-reverse connection circuit is just like the second picture, even...

Rohm's MOSFET is drawn similar to the first picture, without the body diode

stivnnte

bigbat posted on 2019-2-9 12:31 The first figure: C1 and R3 are "integral circuits", mainly used to generate "integral pulses". R1 and R2 are typical voltage divider circuits, mainly providing G ...

VM1 is turned on, isn't it the body diode's fault?

maychang

stivnnte posted on 2020-5-9 14:24 VM1 is turned on, isn't it the body diode?

"VM1 is conducting, isn't it the body diode that's the problem?"

Yes. After power is turned on, the body diode is turned on, and then the P-channel MOS tube is turned on. After the P-channel MOS tube is turned on, the current no longer flows through the body diode.