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In this lesson we will take this motherboard as an example to learn the working process of the standby circuit

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First find the blueprint of this motherboard

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This mainboard is Gigabyte

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Its board number is GA-H110M-S2 and its version number is 1.0

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By searching we found the drawing

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Open the drawing, at the same time we also found the bitmap, open the bitmap

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Next, let's take a look at the standby part of the hard boot of the 100 series mainboard.

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The first step is to supply power to the mainboard by a 3V button battery when the power supply is not plugged in.

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After circuit conversion, the 3V button battery will generate a power supply for the RTC of the bridge

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Let's find this part of the circuit in the mainboard

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We first find the button battery in the physical picture

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Button batteries can be seen here

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Then find the position number of the button battery in the bitmap

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Its position number is BAT

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Search for the position number in the circuit diagram to find the coin cell battery in the circuit diagram

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Let's take a look at this part of the circuit

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First of all, we need to know that the button battery is generally 3.3V

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The electricity of the button battery will generate a N_RTCVDD power supply through the common cathode diode

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Let's search for this power supply and see where it goes

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It can be seen that this power supply is supplied to the VCCRTC pin of PCH

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Then this power supply is used to supply power to the RTC circuit of the bridge.

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At this time, the first step of the sequence has been generated

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Let's draw this step briefly

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Let's look at the second step of the timing

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The second step of the timing sequence is to give the bridge a high-level RTCRST# signal

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after the electricity of the button battery is converted by the circuit.

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Just when VCCRTC was generated, VCCRTC has been pulled up

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N_RTCRST signal

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Let's search for this signal to see where it goes

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As you can see, it is first connected to the RTCRST# pin of the bridge

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This pin is the reset of the RTC circuit

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There is another signal below this signal called SRTCRST#

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Here is also pulled high by VCCRTC

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At the same time, this RTCRST is also connected to a jumper cap

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This jump cap we generally call it a CMOS jump cap

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Then the second step of the timing has also been completed.

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Let's briefly draw this step

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Let's look at the third step of the timing

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In the third step, after the bridge receives the power supply and reset signal of the RTC circuit,

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it will supply power to the crystal oscillator and let the crystal oscillator start to oscillate.

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This crystal oscillator is a 32.768KHz crystal oscillator, which is the crystal oscillator of the RTC circuit

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The crystal oscillator pin of the general bridge is RTCX

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We search for RTCX directly in the circuit diagram

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It can be seen that it is connected to a 32.768KHz crystal oscillator

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In this step we also draw it

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After the crystal oscillator of the RTC circuit also starts to oscillate, the RTC circuit is over.

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Next, let's look at the timing and see what the next step is

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Observing the hard start sequence, we can know that it is the turn of the power supply next

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As long as the ATX power supply is connected to the power supply, it will generate purple 5V, also called 5VSB

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This power supply is uncontrolled

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As long as the power supply has power, it will generate

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Let's find this purple 5V in the circuit diagram

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First find the ATX socket on the mainboard

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It can be seen here that the 5VSB of the purple 5V is the fourth pin from the top to the bottom on the left

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In the real thing, this pin is purple 5V

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Let's draw this purple 5V first

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After the purple 5V is available, it will be converted into a 3.3V voltage by a voltage regulator

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This 3.3V voltage is the deep sleep standby voltage, which is mainly used to power the bridge and IO

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We generally call this power supply VCCDSW_3P3

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This is also a standby condition for the bridge

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Let's find this VCCDSW_3P3 in the circuit diagram

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As you can see, its external name is 3VDUAL_PCH

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Let's search for this power supply to see how it is generated

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After searching, it is found that it is generated by purple 5V through a voltage regulator

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Let's find this voltage regulator in the physical picture

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The model number of this regulator is 1117

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The appearance of the voltage regulator is similar to the symbol in this circuit diagram

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Let's look in the real thing to see if there are similar components

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It can be seen that there is a similar component on the lower right foot of the bridge

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Its position number is NQ9

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Let's go back to the circuit diagram

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It can be seen that the position number of this regulator is also NQ9

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Then this regulator tube is the conversion regulator tube of VCCDSW_3P3

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Let's also briefly draw this step

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After this power supply is generated, it will first give to the VCCDSW_3P3 of the bridge

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Let's see where else this power supply goes

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Continue searching for 3VDUAL_PCH in the circuit diagram sequentially from top to bottom

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It can be seen that in this circuit,

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3VDUAL_PCH replaces the button battery and supplies power to the RTC circuit of the bridge.

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The purpose of this is to save the power of the button battery

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When plugged in, it uses the power of the power supply instead of the button battery

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Prevent the button battery from being consumed too quickly,

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so you don't need to replace the battery frequently

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Let's go down and see where else it's gone

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It can be seen here that it is renamed IT_VCCH through a direct-connected L zero-ohm resistor

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This IT_VCCH is the IO power supply

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This IO is on the lower left foot of the mainboard

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You can see that it is given to the 3VSB pin of the IO

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Let's draw this step as well

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Let's move on to the timing next step

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After the IO detects that the voltage is normal, it will send a deep sleep standby voltage good signal to the bridge

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This deep sleep standby voltage good signal is DSW_PWROK

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Let's search for this DSW_PWROK

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Search for DSW_PWROK in the circuit diagram

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As you can see, its external name is N_PCH_DPWROK

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Let's search for this signal to see where it's coming from

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It is pulled up by 3VDUAL_PCH here

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While 3VDUAL_PCH has generated

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So the pull-up voltage already exists

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Next he also connects to the IO

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When IO has 3VSB power supply, it will issue this N_PCH_DPWROK

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So at this time, the signal has already been generated

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Let's draw this step as well

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Next, after the bridge receives VCCDSW_3P3 and DSW_PWROK, it will send SLP_SUS# signal

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This signal is mainly used to control the main standby voltage, which is VCCPRIM_3P3

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Next, let's take a look at how VCCPRIM_3P3 is generated in the circuit diagram

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Search for VCCPRIM_3P3 in the circuit diagram

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Its external name is VCC3_PCH

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Search for VCC3_PCH

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It can be seen that it is directly converted from 3VDUAL

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We search 3VDUAL

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There are many places where 3VDUAL is connected.

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Let's take a look at it in turn to see where it comes from.

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It can be seen that 3VDUAL is also generated by a voltage regulator

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It's just that the model of this regulator is L1085D

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And its input voltage is not 5VSB, but 5VDUAL

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Let's first find this voltage regulator in the physical picture

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You can see this regulator here, its position number is Q4

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Although this voltage regulator can directly generate 3VDUAL,

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the power supply of the voltage regulator is the input 5VDUAL,

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and we haven't found its source yet.

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We then look for the source of this 5VDUAL

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We found the source of 5VDUAL here

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It can be seen that it connects two MOS tubes

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The MOS tube above is an N-channel MOS tube

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The MOS tube below is a P-channel MOS tube

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This is Gigabyte's characteristic circuit, dual 5V power supply

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5VDUAL is connected to VCC through an N-channel MOS transistor, which is the red 5V after triggering

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Here is a P-channel MOS tube

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5VDUAL is connected to 5VSB through a P-channel MOS tube, which is the purple 5V before power-on

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When the lower tube is turned on, 5VDUAL and 5VSB are connected

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When the upper tube is turned on, 5VDUAL is connected to VCC

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It has not been triggered yet, so the MOS tube below should be turned on

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It is a P-channel MOS tube

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P-channel MOS transistor low-level conduction

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Let's find P_EN and see how it becomes low

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As you can see, it is connected to 5VAUX_SW

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We search for 5VAUX_SW and we can see that it is connected to IO

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This 5VAUX_SW is pulled low after the IO has power supply,

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and does not use the SLP_SUS signal sent by the bridge.

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So there is a low-level 5VAUX_SW signal here, and then there is a 5VDUAL power supply

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With 5VDUAL power supply, there is 3VDUAL power supply

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Let's draw this step a little bit

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After the 3V power supply is generated, the 3V power supply will supply power to the VCCPRIM_3P3 of the bridge

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Then this 3V standby voltage will generate 1V standby voltage, also called VCCPRIM_1P0

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Search for VCCPRIM_1P0 in the circuit diagram

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As you can see, its external name is VCC1_0_PCH

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Let's search for this power supply to see how it is generated

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This power supply is generated by the PWM circuit

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The chip for this PWM is here

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The working process of this chip is very simple, as long as there is power supply and open signal, it will have output

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Its power supply comes from 5VDUAL, which has generated

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And its turn-on signal has not been found

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Let's search

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It can be seen that its turn-on signal comes from this circuit

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These MOS tubes are not installed, all are crossed

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And this is directly connected

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That is to say, the 1V EN signal is directly pulled up by the 3VDUAL through the 8.2k resistor.

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With the power supply, after it is turned on, it will generate a 1V standby voltage

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Let's draw this step as well.

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The power supply comes from 5VDUAL, turn on the pull-up from 3VDUAL

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With the power supply and open signal, the power supply of VCCPRIM_1P0 will be generated

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Next we come to the last step of looking at the machine

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After the IO detects that the standby voltage is normal, it will send a good standby voltage signal RSMRST#

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Let's search for RSMRST#

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You can see that there is an RSMRST here, and an RSMRST here

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The above RSMRST is pulled up by 3VDUAL through a 22K resistor

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And the following RSMRST

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None of these components are installed, let's see where RSMRST went

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It can be seen that it is connected to the bridge and connected to the 114 pin of the IO

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Let's find out if he is still connected to other places

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There is none left

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This signal is pulled up to the bridge by 3VDUAL after it is sent by IO

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But the hard start here says that the IO will send out the RSMRST# signal

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after it detects that the standby voltage is good.

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IO is through pin 95 to judge whether the main standby is normal

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We search for its external signal name and we can see that it is converted from 3VDUAL through a 100 ohm resistor

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3VDUAL is now normal, then the 95 pin of IO will have 3V power supply

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IO will send a high-level RSMRST# signal

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Let's draw this step as well

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After IO gets SUS_3VSB, it will send RSMRST# signal

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The main function of RSMRST# is to give the bridge to tell the bridge that the standby voltage is normal

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Well, so far the standby circuit is over