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How does this circuit start up?

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7

$begingroup$

I'm trying to understand how CI HT7A6322 starts up.

Relevant part of the datasheet says:

Control circuit power supply. Also provides a charging current during start
up due to a high voltage current source connected to SW. For this purpose,
a hysteresis comparator monitors the VCC voltage and provides two
thresholds:

VCCON: Voltage value (typically 14.5V) at which the device starts switching
and turns off the start up current source.

VCCOFF: Voltage value (typically 8V) at which the device stops switching and
turns on the start up current source

When the circuit is connected to mains the internal current source is ON state which is connected together with SW pin.

This current source in winding A induces a voltage in winding B powering the VCC pin. Is my explanation correct?

power-supply transformer switch-mode-power-supply vcc

share|improve this question

edited Sep 21 at 15:41

DIP4

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  Check section High Voltage Start up on page 5 of the link you provided.
  $endgroup$
  – Huisman
  Sep 19 at 19:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I get it. The trick part is ".. which will charge the VCC pin ... ". I think the correct one should be " ... which will charge external capacitor connected in VCC pin ...".
  $endgroup$
  – DIP4
  Sep 19 at 20:00
  

  
  
  
  

add a comment
 | 

7

$begingroup$

I'm trying to understand how CI HT7A6322 starts up.

Relevant part of the datasheet says:

Control circuit power supply. Also provides a charging current during start
up due to a high voltage current source connected to SW. For this purpose,
a hysteresis comparator monitors the VCC voltage and provides two
thresholds:

VCCON: Voltage value (typically 14.5V) at which the device starts switching
and turns off the start up current source.

VCCOFF: Voltage value (typically 8V) at which the device stops switching and
turns on the start up current source

When the circuit is connected to mains the internal current source is ON state which is connected together with SW pin.

This current source in winding A induces a voltage in winding B powering the VCC pin. Is my explanation correct?

power-supply transformer switch-mode-power-supply vcc

share|improve this question

edited Sep 21 at 15:41

DIP4

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  Check section High Voltage Start up on page 5 of the link you provided.
  $endgroup$
  – Huisman
  Sep 19 at 19:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I get it. The trick part is ".. which will charge the VCC pin ... ". I think the correct one should be " ... which will charge external capacitor connected in VCC pin ...".
  $endgroup$
  – DIP4
  Sep 19 at 20:00
  

  
  
  
  

add a comment
 | 

$begingroup$

I'm trying to understand how CI HT7A6322 starts up.

Relevant part of the datasheet says:

Control circuit power supply. Also provides a charging current during start
up due to a high voltage current source connected to SW. For this purpose,
a hysteresis comparator monitors the VCC voltage and provides two
thresholds:

VCCON: Voltage value (typically 14.5V) at which the device starts switching
and turns off the start up current source.

VCCOFF: Voltage value (typically 8V) at which the device stops switching and
turns on the start up current source

When the circuit is connected to mains the internal current source is ON state which is connected together with SW pin.

This current source in winding A induces a voltage in winding B powering the VCC pin. Is my explanation correct?

power-supply transformer switch-mode-power-supply vcc

share|improve this question

edited Sep 21 at 15:41

DIP4

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

$endgroup$

share|improve this question

edited Sep 21 at 15:41

DIP4

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

share|improve this question

edited Sep 21 at 15:41

DIP4

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

asked Sep 19 at 19:27

DIP4DIP4

8155 bronze badges

2 Answers
2

active

oldest

votes

8

$begingroup$

At the top of the block diagram on page 2, there's a MOSFET that functions as a current source connected between SW and VCC that can withstand the full line voltage. It passes a tiny current (via winding "A" of the transformer) that doesn't cause too much dissipation inside the device. This current is not sufficient for operation of the switching regulator, however.

This current source charges the capacitor attached to VCC until it reaches Vccon, at which point, the switching begins (powered temporarily by the charge on the capacitor) and larger amounts of power can be transferred via the auxiliary winding "B" on the transformer to keep things going continuously.

share|improve this answer

edited Sep 19 at 20:00

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

$endgroup$

add a comment
 | 

11

$begingroup$

Normally we are using the start-up resistor. But in this case, there is an internal MOSFET between SW and VCC pin. And this MOSFET will provide a start-up current.

share|improve this answer

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  +1 for referring to the datasheet... The datasheet saves all! :)
  $endgroup$
  – KingDuken
  Sep 19 at 19:55
  

  
  
  
  

add a comment
 | 

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8

$begingroup$

At the top of the block diagram on page 2, there's a MOSFET that functions as a current source connected between SW and VCC that can withstand the full line voltage. It passes a tiny current (via winding "A" of the transformer) that doesn't cause too much dissipation inside the device. This current is not sufficient for operation of the switching regulator, however.

This current source charges the capacitor attached to VCC until it reaches Vccon, at which point, the switching begins (powered temporarily by the charge on the capacitor) and larger amounts of power can be transferred via the auxiliary winding "B" on the transformer to keep things going continuously.

share|improve this answer

edited Sep 19 at 20:00

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

$endgroup$

add a comment
 | 

8

$begingroup$

At the top of the block diagram on page 2, there's a MOSFET that functions as a current source connected between SW and VCC that can withstand the full line voltage. It passes a tiny current (via winding "A" of the transformer) that doesn't cause too much dissipation inside the device. This current is not sufficient for operation of the switching regulator, however.

This current source charges the capacitor attached to VCC until it reaches Vccon, at which point, the switching begins (powered temporarily by the charge on the capacitor) and larger amounts of power can be transferred via the auxiliary winding "B" on the transformer to keep things going continuously.

share|improve this answer

edited Sep 19 at 20:00

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

$endgroup$

add a comment
 | 

$begingroup$

At the top of the block diagram on page 2, there's a MOSFET that functions as a current source connected between SW and VCC that can withstand the full line voltage. It passes a tiny current (via winding "A" of the transformer) that doesn't cause too much dissipation inside the device. This current is not sufficient for operation of the switching regulator, however.

This current source charges the capacitor attached to VCC until it reaches Vccon, at which point, the switching begins (powered temporarily by the charge on the capacitor) and larger amounts of power can be transferred via the auxiliary winding "B" on the transformer to keep things going continuously.

share|improve this answer

edited Sep 19 at 20:00

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

$endgroup$

share|improve this answer

edited Sep 19 at 20:00

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

answered Sep 19 at 19:41

Dave Tweed♦Dave Tweed

143k1111 gold badges187187 silver badges323323 bronze badges

11

$begingroup$

Normally we are using the start-up resistor. But in this case, there is an internal MOSFET between SW and VCC pin. And this MOSFET will provide a start-up current.

share|improve this answer

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  +1 for referring to the datasheet... The datasheet saves all! :)
  $endgroup$
  – KingDuken
  Sep 19 at 19:55
  

  
  
  
  

add a comment
 | 

11

$begingroup$

Normally we are using the start-up resistor. But in this case, there is an internal MOSFET between SW and VCC pin. And this MOSFET will provide a start-up current.

share|improve this answer

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  +1 for referring to the datasheet... The datasheet saves all! :)
  $endgroup$
  – KingDuken
  Sep 19 at 19:55
  

  
  
  
  

add a comment
 | 

$begingroup$

Normally we are using the start-up resistor. But in this case, there is an internal MOSFET between SW and VCC pin. And this MOSFET will provide a start-up current.

share|improve this answer

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges

$endgroup$

share|improve this answer

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges

answered Sep 19 at 19:48

G36G36

6,61311 gold badge77 silver badges1212 bronze badges