(standby) power.

29 Pages·2015·0.85 MB·English

Low Standby ACDC Power
Converter Design
Tony Liu
Analog FAE
[email protected]
USB Chargers, Small Adapters and Aux
power
• Different application requirements
– Cell phone & tablet battery chargers, 5~20 W
– Low power adapters, 10~30 W
– Medium-power adapters, 30~65 W
– AUX (standby) power.

• Must meet different standard requirements
– Energy Star efficiency requirement
– 5-Star rating for standby power
– Regulation and transient response
– EN55022 EMI standard

• Often conflicting design targets
– High efficiency vs. low standby
– High output power vs. small size
– High performance vs. low cost
Efficiency and Standby Power Requirement
• Recent directives from
EC Code of Conduct
and US Dept. of Energy,
for example, are driving
minimum efficiency
requirements higher.
• EC CoC drives standby
power requirements to
new lows, such as Tier 2
in January 2016.
• 5-Star rating system
allows 5 stars placed on
chargers with no-load
power less than 30 mW.
Progression of Standby Power
• Mobile phone consortium established the 5-Star rating system to
encourage development of chargers with lower standby power.
• Recent marketing efforts are driving the target to 10 mW and below.
• This target is being applied not only to cell phone chargers, but video
displays and other appliances, too.
Origin of “Zero-Power” Designation
• National environmental agencies around the world refer to standards
developed by international commissions when setting local policy.

• IEC 62301 “Household Electrical Appliances – Measurement of Standby
Power” standardizes measurement methods of standby power in various
appliances and electronic equipment.
– Performance parameters of measurement equipment are specified
– Test conditions and procedures are specified
– Clause 4.5 regards measurements of less than 5 mW as zero power

• Clause 4.5 of IEC 62301 has become the basis for a “Zero-Power” marketing
campaign as the ultimate target for no-load standby dissipation in electronic
devices and appliances.
Progression Towards Zero-Power ~ 2006
“Green-Mode” Quasi-Resonant
PRIMARY SECONDARY
+ + Flyback Controller
VBULK CBULK RSU RSNUB CSNUB N1 N2 COUT VOUT ROUT
-
- Standby less than 200 mW
VAC CDD RDD NB
ROVP1
Standby Power vs. Input Voltage
Input Power vs Input Voltage at No Load
UCC28600
220 mW
1 SS STATUS 8 230
CSS
210
191 mW
FEEDBACK
2 FB OVP 7 190
ROVP2 )W 170
3 CS VDD 6 m
142 mW
( r 150 140 mW
M1 ew
4 GND OUT 5 oP 130
t
TL431 up 110
n
I
CBP 90
100nF
70
RPL
RCS 50
50 85 100 115 150 200 230 250 265
Major standby loss paths Input Voltage (Vac)
Input Power vs Input Voltage at no Load
6
Simplify the Flyback: Opto FB Vs PSR
• SSR • PSR
Primary Secondary Primary Secondary
+ CB1 CB2 COUT VOUT + CB1 CB2 NP NS COUT VOUT
– –
VAC VAC
R
F1
CONTROLLER CONTROLLER
Auxiliary Auxiliary
VDD HV R R VDD HV
F2 F3
CDD NA CDD
RS1 DRV C RS1 DRV
VS C1 VS
TL431
RS2 CS RS2 CS
R
F4
FB RCS RCS
R GND GND
F6
PSR Benefits and Limitations
• Benefits
• Opto-coupler and TL431 circuits are eliminated
• Less parts = lower cost, smaller adapter, higher reliability
• Easier to use – internal loop compensation
• Limitations
• Transient Response performance linked to no-load power
performance.
• Lower minimum frequency gives lower no-load power dissipation.
• Lower minimum frequency means a longer response time to load transient from
no-load to full load.
• Transient response can be improved by the addition of a secondary
side wake up circuits (IC).
Progression Towards Zero-Power ~ 2011
Example 1 Example 2
UCC28700 DCM PSR UCC28710 DCM PSR
Flyback Controller HV-Input Flyback Controller

Standby less than 30 mW Standby less than 10 mW
VBLK VREG RCB VBLK VREG RCB
+ CB1 CB2 Np NNss COUT RPL VOUT + CB1 CB2 Np Ns COUT RPL VOUT
RSTR
– –
VAC
VAC
UCC28710
UCC28700 SOIC-7
SOT23-6
VAUX D2
VAUX VDD HV
VDD
Na RS1 D2 CDD DRV Na RS1 CDD DRV
VS VS
CS CS
RS2 TBD RLC RCS RS2 TBD RLC RCS
GND GND
Test Data from 5-W charger: Test Data from 5-W charger:
24.3 mW @ 230 Vac 7.8 mW @ 230 Vac
Major standby loss paths
Features Enabling Zero Standby Power
 Bias Supply
 Integrated high-voltage switch eliminates constant start-up current
 High operating bias voltage, up to 35 V  high N /N ratio
AUX SEC
 Wide UVLO hysteresis allows VDD to drop as low as ~8 V during standby
without triggering UVLO

 Dynamic IC Power Management
 Very low bias current during standby (~50 uA)
 IC has low power wait-state between pulses at f < 28 kHz to reduce IC
SW
consumption to < 1 mW in standby
 Wake-up capability ensures rapid response to sudden load steps while in
standby condition

 Wide Power-Control Dynamic Range
 Switching frequency extends from 83 kHz down to 30 Hz
 3 : 1 variation in primary peak current