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SMPS housekeeping electronics power question

Started by Unknown June 1, 2012
Could some electronics guru please clarify a bit ?
How is power to the control electronics circuitry 
of an SMPS provided -- power for controller/PWM 
module ? Any hints, suggestions or pointers to 
relevant information would be helpful.
 
On Fri, 1 Jun 2012 18:41:31 -0700 (PDT), the renowned
dakupoto@gmail.com wrote:

>Could some electronics guru please clarify a bit ? >How is power to the control electronics circuitry >of an SMPS provided -- power for controller/PWM >module ? Any hints, suggestions or pointers to >relevant information would be helpful. >
Sometimes it's bootstrapped off of the output with a resistor or FET or linear regulator to the line to allow it to startup. Since that's too wasteful with a big switcher, bigger supplies often have a small auxilliary switching supply that starts up as above and supplies the control electronics of the big guy with a few watts of power. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Many options:
1. Circuit starts on its own.  Example: self-oscillating (one or two 
transistor) oscillator.  A small bias current, provided by a large resistor, 
starts the reaction.

2. Passive.  Flyback and forward converters often use a UC3842, TOPSwitch or 
other controller, which draws little current until supply voltage reaches a 
threshold.  Thus, it can be charged up from zero, using a small bias current 
from the rectified line.  Once the controller starts, current consumption 
rises, so an auxiliary supply (usually derived from the same transformer) is 
required.

This is arguably the same as 1., but the circuit is much more complex and 
won't run on startup current alone, whereas in 1., the circuit operates 
continuously due to the bias current thus provided.

3. Auxiliary.  A separate power supply can be provided (which itself uses 
one of the above methods, or a line-frequency transformer) which powers the 
controller.  This can provide startup current alone (in which case, another 
auxiliary method takes over, as is the case for 2.), or it's addutionally 
used to supply other loads as well.  This method is typically used in high 
power supplies, where the controller recieves feedback and error signals 
from the output side; drive is coupled to the line side with isolation 
(usually transformers).

The classical ATX computer PSU uses this method, using a single-transistor 
oscillator (type 1) to provide standby power (which operates the controller 
as well as standby functions on the motherboard).  The controller is 
typically a TL494 or variant, using a transformer to couple signals to the 
transistors (often BJTs).

High power systems often use many auxiliary supplies, so that active power 
is available *at* the power switch inputs, enabling gate drivers to operate 
very large transistors.  In a power supply with three half-bridge IGBT 
modules, this requires six separate isolated power supplies, in addition to 
the controller's power supplies.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

<dakupoto@gmail.com> wrote in message 
news:40615889-8c6b-4bdb-a03e-1aed44834976@googlegroups.com...
> Could some electronics guru please clarify a bit ? > How is power to the control electronics circuitry > of an SMPS provided -- power for controller/PWM > module ? Any hints, suggestions or pointers to > relevant information would be helpful. >
On Friday, June 1, 2012 10:16:07 PM UTC-4, Tim Williams wrote:
> Many options: > 1. Circuit starts on its own. Example: self-oscillating (one or two > transistor) oscillator. A small bias current, provided by a large resistor, > starts the reaction.
I guess the initial bias current is obtained from the AC power switch-on ? The start-up is the main issue here.
> > 2. Passive. Flyback and forward converters often use a UC3842, TOPSwitch or > other controller, which draws little current until supply voltage reaches a > threshold. Thus, it can be charged up from zero, using a small bias current > from the rectified line. Once the controller starts, current consumption > rises, so an auxiliary supply (usually derived from the same transformer) is > required. > > This is arguably the same as 1., but the circuit is much more complex and > won't run on startup current alone, whereas in 1., the circuit operates > continuously due to the bias current thus provided. > > 3. Auxiliary. A separate power supply can be provided (which itself uses > one of the above methods, or a line-frequency transformer) which powers the > controller. This can provide startup current alone (in which case, another > auxiliary method takes over, as is the case for 2.), or it's addutionally > used to supply other loads as well. This method is typically used in high > power supplies, where the controller recieves feedback and error signals > from the output side; drive is coupled to the line side with isolation > (usually transformers). > > The classical ATX computer PSU uses this method, using a single-transistor > oscillator (type 1) to provide standby power (which operates the controller > as well as standby functions on the motherboard). The controller is > typically a TL494 or variant, using a transformer to couple signals to the > transistors (often BJTs). > > High power systems often use many auxiliary supplies, so that active power > is available *at* the power switch inputs, enabling gate drivers to operate > very large transistors. In a power supply with three half-bridge IGBT > modules, this requires six separate isolated power supplies, in addition to > the controller's power supplies. > > Tim > > -- > Deep Friar: a very philosophical monk. > Website: http://webpages.charter.net/dawill/tmoranwms > > <dakupoto@gmail.com> wrote in message > news:40615889-8c6b-4bdb-a03e-1aed44834976@googlegroups.com... > > Could some electronics guru please clarify a bit ? > > How is power to the control electronics circuitry > > of an SMPS provided -- power for controller/PWM > > module ? Any hints, suggestions or pointers to > > relevant information would be helpful. > >
<dakupoto@gmail.com> wrote in message 
news:3a98354c-3919-4ac3-a0d6-4d44c84466b2@googlegroups.com...
> On Friday, June 1, 2012 10:16:07 PM UTC-4, Tim Williams wrote: > > Many options: > > 1. Circuit starts on its own. Example: self-oscillating (one or two > > transistor) oscillator. A small bias current, provided by a large > > resistor, > > starts the reaction. > > I guess the initial bias current is obtained from the > AC power switch-on ? The start-up is the main issue here.
This type of circuit is entirely line operated, so the bias comes from the rectified line. Although many designs exist, a prominent one is the flyback type blocking oscillator: http://myweb.msoe.edu/williamstm/Images/Blocking%20Oscillator.gif Here's a more developed version. Both BJTs and MOSFETs can be used as the main switch, though BJT is more common due to the ease of drive and low cost. http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Fast_DCDC.png Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms