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Low standby power offline SMPS

treez
Intellectual 970 points
Other Parts Discussed in Thread: UCC28600, UCC28600EVM-65W

hello, 


I apologise for this long post...though if you are a little knowledgable about SMPS's , then this will be straightfroward, just a spec sheet of an SMPS......... 


i wish to design an isolated, offline SMPS and i am wondering if i have missed hearing about any new   ti.com  "low standby power" SMPS controllers? 

V(in) = 85 to 265VAC 
V(out)_1 = 36V +/- 10% 
V(out)_2 = 5V +/- 4% 

V(out)_1 and V(out)_2 must be isolated SELV outputs. 

The 5V rail has maximum power of 2W 
The 36V rail has a maximum "running" power of 10W. 
(-but see below for its peak power of 36W) 
Both 36V and 5V rails could have power levels anywhere from 200mW to their maximum, at any given moment. 

In "standby", the 5V rail will have a load of 170mW. (170mW is the average power.......though the load is being switched on/off at frequency of 0.1 to 10Hz)
In "standby", the 36V rail is not needed at all, and could be shut down in some way. 

In "standby", the SMPS must draw no more than 500mW from the mains (yes, just 500mW). 

The 36V rail is interesting.....it has a 30mF (yes, 30mF)capacitor across it.......when the SMPS is switched on at the mains, this 30mF capacitor must be charged up to 36V. -This 30mF capacitor must attain 36V within 1 second of the SMPS being switched on at the mains. 

-When this 30mF capacitor is charged up to 36V, then the load on the 36V rail is 10W maximum 
-This 30mF capacitor exists to provide some power to both the 36V rail and the 5V rail in the event of a mains failure. 
-When the 30mF capacitor is being charged up, there is no other load on the 36V rail other than this charging capacitor. 

-The big challenge with this is 1) the peak load of 38W while the 30mF capacitor is charging.....2) Even bigger challenge is the 500mW maximum power drawn from the mains when in "standby" mode............as you know, in "standby" mode, the secondary (specifically the 5V rail) has a 170mW load on it.......assuming 80% efficiency, this means a 213mW load seen at the primary........meaning that that we only have 287mW of margin before we violate the 500mW power consumption. 

 

Also, another challenge is that the auxiliary rail  may drop out when in "standby" mode.

-Do you know of a ti.com controller thats good for this?

  • 0
    TI__Guru 73575 points

    Can you consider UCC28600?

  • 0 in reply to Hong Huang
    Intellectual 970 points

    unfortunatley ucc28600 is a quasi resonant controller, and these have  relatively high power draw when in standby.

     

    it needs to be a controller with skip cycle in standby...as well as current peak reduction......unfortunately, QR controllers just dont operate well like this, and also, QR controllers have terribly high peak currents...compared to continuous mode flybacks

  • 0 in reply to treez
    TI__Guru 73575 points

    less than 500mW standby input power has been achieved in various designs with UCC28600. You may evaluate our UCC28600EVM-65W to give it a test and find out if it is good to your applications. QR is not necessarily an issue. At the load level of your application needs, continuous mode current control may not bring more benefit than QR or critical conduction mode control flybck.