SR086/SR087 Adjustable Offline Inductorless Switching Regulators Data Sheet

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 2017 Microchip Technology Inc.

DS20005544A-page  1

SR086/SR087

Features

• Efficient Operation without Magnetics
• No High-voltage Capacitors
• Adjustable Main Output Voltage (9V to 50V)
• Additional Internal Linear Regulator:

- 3.3V for SR086
- 5V for SR087

• Up to 100 mA Combined Output Current
• Single BOM for 120 VAC/230 VAC
• Built-in Soft Start
• Less than 200 mW Standby Power

Applications

• White Goods
• Household Appliances
• Lighting Controls
• Circuit Breakers
• Keep-alive Supplies

General Description

The  SR086/SR087 are inductorless switching 
regulators designed to operate directly from a rectified 
AC line. The operating principle is to turn on a pass 
transistor when the rectified AC is below the output 
voltage and to turn it off when the output voltage 
reaches a specific level. The ICs feature an adjustable 
main output voltage of 9V to 50V and an additional 
fixed output of 3.3V for SR086 and 5V for SR087. 
Efficiencies of around 55% may be realized for loads 
up to 1W in 120 VAC applications and about 50% 
efficiencies for loads up to 800 mW in 230 VAC 
applications.
A logic-level enable input allows the SR086/SR087 to 
be disabled—useful when they are employed as 
keep-alive power supplies.

Package Type

Backside on the SOIC package is at ground potential and may be connected to 
ground or left unconnected. See 

Table 2-1

 for pin information.

8-lead SOIC   

(with Heat Slug)

(Top view)

1

2

3

4

8

7

6

5

VIN

EN

GND

VREG

GATE

VGD

VOUT

VFB

Heat Slug

WARNING

Galvanic isolation is not provided. Dangerous voltages are present when connected to the AC line. It is 
the responsibility of the designer using the SR086/SR087 to ensure that adequate security measures are 
in place to protect the end user from electrical shock.

The circuits shown in this data sheet are not guaranteed to meet surge and conducted EMI 
requirements. The effectiveness of these circuits may vary with a particular application. The designer 
must conduct tests to ascertain compliance with applicable standards and regulations.

Adjustable Offline Inductorless Switching Regulators

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SR086/SR087

DS20005544A-page  2

 2017 Microchip Technology Inc.

Functional Block Diagram

1.0kV
1.0A

275V

50A

90 to

270VAC

50/60Hz

R

GD

1.1MΩ

STGD5NB120SZ

 V

OUT

  - 1

1.25V

R

FB(HI) 

= R

FB(LO)

3.3V

C

REG

100nF

GND

VREG

FB

VOUT

VGD

GATE

VIN

EN

1.25A

9.0 - 50VDC

SR086

R

FB(LO)

12.4k

Ω

C

GD

100nF

C

OUT

470μF

R

PD

390kΩ

C

OUT1

1.0μF

Upper circuitry
powered by V

GD 

- V

OUT

Lower circuitry
powered by V

OUT 

- GND

Level
Translator

1.25V

REG

R

    Q

S

13V

s

1.0kV
1.0A

275V

50A

90 to

270VAC

50/60Hz

R

GD

1.1MΩ

STGD5NB120SZ

 V

OUT

  - 1

1.25V

R

FB(HI) 

= R

FB(LO)

5.0V

C

REG

100nF

GND

VREG

FB

VOUT

VGD

GATE

VIN

EN

1.25A

9.0 - 50VDC

SR087

R

FB(LO)

12.4k

Ω

C

GD

100nF

C

OUT

470μF

R

PD

390kΩ

C

OUT

1

1.0μF

Upper circuitry
powered by V

GD 

- V

OUT

Lower circuitry
powered by V

OUT 

- GND

Level
Translator

1.25V

REG

R

    Q

S

13V

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DS20005544A-page  3

SR086/SR087

Typical Application

1.0kV
1.0A

275V

50A

90 to 

270VAC

50/60Hz

390kΩ

1.1MΩ

STGD5NB120SZ

 V

OUT

  - 1

1.25V

R

= R

2

3.3V
@60mA

100nF

GND

VREG

FB

VOUT

VGD

GATE

VIN

EN

Enable

1.25A

V

OUT

9.0 - 50VDC
@100mA - I

REG

SR086

R

2

12.4k

Ω

1.0μF

100nF

470μF

 Circuits

1.0kV
1.0A

275V

50A

90 - 

270VAC

50/60Hz

390kΩ

1.1MΩ

STGD5NB120SZ

 V

OUT

  - 1

1.25V

R

= R

2

5.0V
@60mA

100nF

GND

VREG

FB

VOUT

VGD

GATE

VIN

EN

Enable

1.25A

V

OUT

9.0 - 50VDC
@ 100mA - I

REG

SR087

R

2

12.4k

Ω

1.0μF

100nF

470μF

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SR086/SR087

DS20005544A-page  4

 2017 Microchip Technology Inc.

1.0

ELECTRICAL CHARACTERISTICS

Absolute Maximum Ratings †

Output Voltage, V

OUT

..................................................................................................................................–0.3V to 56V

Feedback Voltage, V

FB

..............................................................................................................................–0.3V to 6.5V

Enable Voltage, V

EN

...................................................................................................................................–0.3V to 6.5V

Operating Junction Temperature, T

J

.................................................................................................... –40°C to +125°C

 Notice: Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the 
device. This is a stress rating only, and functional operation of the device at those or any other conditions above those 
indicated in the operational sections of this specification is not intended. Exposure to maximum rating conditions for 
extended periods may affect device reliability.

RECOMMENDED OPERATING CONDITIONS

Parameter

Sym.

Min.

Typ.

Max.

Unit

Conditions

Output Voltage 

V

OUT

9

50

V

Load on V

OUT

, including Feedback Divider and Load on V

REG

I

OUT 

100 

µA

Headroom for Internal Linear Regulation (V

OUT

–V

REG

)

V

HR

4

V

ELECTRICAL CHARACTERISTICS

Electrical Specifications: Unless otherwise noted, T

A

 = –40°C to +85°C. Voltages referenced to GND pin.

Parameter

Sym.

Min.

Typ.

Max.

Unit

Conditions

Current Consumption at V

GD

I

GD

60

µA

Current Consumption of the Lower Circuitry

I

OUT(INT)

400

µA

V

OUT 

= 9V–50V

Gate Drive Supply Voltage

V

GD

11

13

15

V

Note 1

Gate Output High Voltage 

V

GATE(HI)

11

15

V

Note 1

Gate Output Low Voltage 

V

GATE(LO)

0.5

V

Note 1

Feedback Voltage (Gate Off)

V

FB(OFF)

1.18

1.25

1.31

V

Feedback Voltage (Hysteresis)

V

FB(HYST)

50

mV

Feedback Input Current

I

FB

500

nA

V

IN

 Trip Voltage (Gate On) 

V

TRIP(ON)

0

3

V

Note 1

V

IN

 Trip Voltage (Gate Off) 

V

TRIP(OFF)

9

15

V

Note 1

Enable Voltage, On

V

EN(ON)

0.2

V

Enable Voltage, Off

V

EN(OFF)

0.75

V

REG

V

IN

 Gate Turn-on Delay

t

DIG(ON)

0

1

µs

C

GATE

 = 1 nF

V

IN

 Gate Turn-off Delay

t

DIG(OFF)

600

ns

C

GATE

 = 1 nF

Feedback Gate Turn-off Delay

t

DFG(OFF)

450

ns

C

GATE

 = 1 nF, V

FB 

= 1.5V

Regulated Output Voltage 

SR086

V

REG

3.125 

3.3

3.465

V

I

LOAD

 = 1 mA, V

OUT 

= 9V

SR087

4.750

5

5.250

V

V

REG 

Load Regulation

Δ

V

REG

–50

+50

mV

0 mA < I

LOAD

 < 60 mA,

V

OUT 

= 9V, T

AMB 

= 25°C

Gate V

GD

 Diode Drop

V

D

1

V

I = 20 mA

Note 1: Referenced to V

OUT

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TEMPERATURE CHARACTERISTICS

Electrical Characteristics: Unless otherwise noted, for all specifications T

A

 =T

J

 = +25°C.

Parameter

Sym.

Min. Typ.

Max.

Unit

Conditions

TEMPERATURE RANGE
Operating Junction Temperature

T

J

 

–40

+125

°C 

PACKAGE THERMAL RESITANCE
8-lead SOIC (with Heat Slug) 

θ

JA

84

°C/W

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DS20005544A-page  5

SR086/SR087

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SR086/SR087

DS20005544A-page  6

 2017 Microchip Technology Inc.

SRO86 and SR087 Timing Diagram

Pass Transistor on 

V

IN 

V

OUT 

not to scale 

V

FB(OFF)

   1+  

RF

B(HI) 

      

RF

B(LO) 

Pass Transistor is turned 

on when V

IN 

falls below: 

V

OUT 

+ V

TRIP(ON) 

Pass Transistor is on but 

not conducting since the  

input voltage is lower 

than the output voltage 

Pass Transistor is on 

and conducting 

Pass Transistor is 

turned off once V

OUT 

reaches the trip point 

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DS20005544A-page  7

SR086/SR087

2.0

PIN DESCRIPTION

The descriptions of the SR086/SR087 pins are listed 
on 

Table 2-1

. Refer to 

Package Type

 for the location of 

pins. 

TABLE 2-1:

PIN FUNCTION TABLE 

Pin Number

SR086

Pin Name

SR087

Pin Name

Description

1

VIN

VIN

Rectified AC input voltage

2

EN

EN

Active low enable input

3

GND

GND

Circuit ground (

Note 1

)

4

VREG

VREG

Regulated output voltage (

Note 2

)

5

FB

FB

Feedback input

6

VOUT

VOUT

Output voltage (9V–50V adj.)

7

VGD

VGD

Gate drive supply (referenced to VOUT)

8

GATE

GATE

Drives external IGBT pass transistor

Note 1: Circuit ground will be at the AC line potential. 

2: Fixed 3.3V for SR086 and fixed 5V for SR087

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SR086/SR087

DS20005544A-page  8

 2017 Microchip Technology Inc.

3.0

APPLICATION INFORMATION

D

1

1.0kV
1.0A

Z

1

275V

50A

V

IN

90 to 270VAC

50/60Hz

F

1

1.0A

R

6

12.4k

Ω

R

5

113k

Ω

V

OUT

12.6VDC

*R

4

510k

Ω

*R

3

510k

Ω

*R

1

200k

Ω

*R

2

200k

Ω

* Two resistors used in

series for reasons of

high voltage creepage

and resistor voltage rating.

Enable

R

7

100k

Ω

C

2

1.0μF

C

3

470μF

C

1

100nF

C

4

100nF

V

REG

3.3VDC

Q

1

STGD5NB120SZ

VIN

GATE

VGD

VOUT

FB

VREG

GND

EN

2

3

4

5

6

7

8

1

SR086

FIGURE 3-1:

SR086 Typical Application Circuit.

D

1

1.0kV
1.0A

Z

1

275V

50A

V

IN

90 to 270VAC

50/60Hz

F

1

1.0A

R

6

12.4k

Ω

R

5

113k

Ω

V

OUT

12.6VDC

*R

4

510k

Ω

*R

3

510k

Ω

*R

1

200k

Ω

*R

2

200k

Ω

* Two resistors used in

series for reasons of

high voltage creepage

and resistor voltage rating.

Enable

R

7

100k

Ω

C

2

1.0μF

C

3

470μF

C

1

100nF

C

4

100nF

V

REG

5.0VDC

Q

1

STGD5NB120SZ

VIN

GATE

VGD

VOUT

FB

VREG

GND

EN

2

3

4

5

6

7

8

1

SR087

FIGURE 3-2:

SR087 Typical Application Circuit. 

3.1

Output Voltage

V

OUT 

may be adjusted in the range of 9V to 50V by 

changing feedback resistor R

5

 based on 

Equation 3-1

.

EQUATION 3-1:

R

5

R

6

V

OUT

1.25V

1

=

 

Leave R

6

 at 12.4 kΩ or less as it assures a minimum 

100 µA load required for the proper operation of 
SR086/SR087. Change R

and R

4

 according to 

Equation 3-4

. Select C

2

 and C

3

 with appropriate 

voltage ratings. For C

3

, use a low-ESR capacitor with 

an adequate ripple current rating (800 mA

RMS

). Use 

ceramic for C

2

Since V

REG 

is a linear regulator supplied from V

OUT

the maximum current available from V

REG

 is reduced 

as V

OUT

 is increased due to power considerations. 

Refer to 

Equation 3-2

 for SR086 and 

Equation 3-3

 for 

SR087.

EQUATION 3-2:

I

REG MAX

1.5W

V

OUT

3.3V

------------------------------------

=

or 60 mA, whichever is 
less 

EQUATION 3-3:

I

REG MAX

1.5W

V

OUT

5V

-------------------------------

=

or 60 mA, whichever is 
less 

3.2

Input Voltage

To reduce standby power for 230 VAC-only 
applications or for supply voltages less than 90 Vrms, 
R

3

 and R

4

 should be changed according to 

Equation 3-4

. R

1

+R

2

 should remain at 400 kΩ or less. 

Two resistors in series are used to ensure adequate 
creepage distances for 230 VAC operation. For 120 
VAC-only applications, single resistors may be used.

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DS20005544A-page  9

SR086/SR087

EQUATION 3-4:

R

3

 + R

EQUATION

R

3

R

4

+

2V

IN

2

V

IN

2

V

x

1

V

x

V

IN

----------------------

cos

 25A

--------------------------------------------------------------------------------------

Where: V

x

 = V

OUT

 + 15V

Use the minimum anticipated RMS value for 
V

IN

. Take resistor tolerance into account, 

selecting the next lower standard value. 
Choosing a lower value has no effect other 
than higher standby power.

3.3

Output Ripple

Storage capacitor C

3

 was sized to provide about 2V

P-P

ripple at 100 mA load (I

OUT

 + I

REG

). For lighter loads, 

C

3

 may be reduced. Conversely, C

3

 may be increased 

for lower ripple. Use a low-ESR capacitor with an 
adequate ripple current rating (e.g. 800 mA

RMS

 for 

100 mA loads). Efficiency and output current capability 
may drop with increased capacitance because of a 
smaller conduction angle associated with lower ripple. 
Due to feedback hysteresis, ripple cannot be reduced 
below 4%. See 

Equation 3-5

.

EQUATION 3-5:

V

RIPPLE P P

I

OUT

I

REG

+

 2f

IN

C

3

Note: V

REG

 requires at least 4V of headroom. 

Therefore, V

OUT

, including ripple, must not fall 

below 7.3V for SR086 and 9V for SR087.

3.4

Line Transformer

During initial testing, it is tempting to use an isolation 
transformer or a variable transformer on the AC line. 
However, the high inductance of the transformer 
(frequently in mH range) should not be used because it 
interferes with the normal operation of the 
SR086/SR087. This is not a concern with the normal 
inductance of the AC line or for AC line filters. 

AC Line

SR086

Circuitry

FIGURE 3-3:

Line Transformer. 

As shown in 

Figure 3-3

, the SR086/SR087 draw 

current from the AC line (in short, high current pulses). 
The transformer’s high inductance tends to limit the 
current pulse. Furthermore, inductive kickback on the 
falling edge of the current pulse can create high voltage 
spikes which must be absorbed by the transient 
protector.

3.5

Electromagnetic Interference 
(EMI) Capacitor

Small-value capacitors from circuit common to earth 
ground should not be used as they prevent the 
SR086/SR087 from operating. See 

Figure 3-4

AC Line

SR086 &

Circuitry

earth

ground

circuit

common

FIGURE 3-4:

EMI Capacitor.

3.6

EMI

The  SR086/SR087 circuits, as shown in the 

Functional Block Diagrams

, meet FCC Class B and 

CISPR 14-1 (household appliances) requirements for 
conducted emissions for combined loads of less than 
20 mA (I

OUT

 + I

REG

).

3.7

Fuse

Although the average current drawn from the AC line is 
low, the RMS current is fairly high due to the current 
being drawn in short high-current pulses. Since a fuse 
is basically a resistor with a power dissipation given by 
I

RMS

2

 R, the fuse must be sized for the RMS current 

and not the average current. For a 1W load at 120 VAC, 
the RMS current is 700 mA

RMS

, while the RMS current 

for a 0.5W load at 230 VAC is 360 mA

RMS

.

3.8

Load

Total load on the SR086/SR087 is the total load current 
drawn from V

OUT

 (I

OUT

), and since the linear regulator 

is supplied from V

OUT

, it also includes the current 

drawn from V

REG

 (I

REG

). Total load is calculated in 

Equation 3-6

 and 

Equation 3-7

.

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SR086/SR087

DS20005544A-page  10

 2017 Microchip Technology Inc.

EQUATION 3-6:

I

LOAD

I

OUT

I

REG

+

=

EQUATION 3-7:

P

LOAD

V

OUT

I

OUT

I

REG

+

=

3.9

Uninterruptible Power Supply 
(UPS) 

The SR086/SR087 will not operate from a UPS with a 
square wave output. This type of output is usually 
referred to as “modified sine wave.”

3.10

Transient Protection

The transient protector must be located before the 
bridge rectifier. The reason for this is to minimize 
capacitance to allow the rectified AC to fall below V

OUT

.

Since there is no capacitor to absorb AC line transients, 
complete transient protection must be provided by the 
TVS or MOV device. Since the recommended IGBT is 
rated at 1.2 kV and the SR086/SR087 never see the full 
input voltage, the bridge rectifier becomes the limiting 
element when selecting an MOV. When using a 1 kV 
bridge, an MOV having a clamping voltage of greater 
than 1 kV is recommended.
An RC network on the AC line, as shown in 

Figure 3-5

 

and 

Figure 3-6

, affords additional protection from line 

transients as well as reducing conducted EMI. It does, 
however, reduce power supply efficiency.

R

2

10.0k

Ω

1.0μF

1.0μF
240VAC
X2

1.0kV
1.0A

275V

50A

90 to

270VAC

50/60Hz

200kΩ

STGD5NB120SZ

 V

OUT

   

- 1

1.25V 

R

= R

2

3.3V
@60mA

100nF

GND

VREG

FB

VOUT

VGD

GATE

VIN

EN

Enable

1.0A

V

OUT

9.0 - 50VDC
@ 100mA - I

REG

SR086

100nF

10Ω, 3.0W

Wire Wound

470μF

200kΩ

510kΩ

510kΩ

FIGURE 3-5:

SR086 Additional Transient Protection. 

R

2

10.0k

Ω

1.0μF

1.0μF
240VAC
X2

1.0kV
1.0A

275V

50A

90 to

270VAC

50/60Hz

200kΩ

STGD5NB120SZ

 V

OUT

   

- 1

1.25V 

R

= R

2

5.0V
@60mA

100nF

GND

VREG

FB

VOUT

VGD

GATE

VIN

EN

Enable

1.0A

V

OUT

9.0 - 50VDC
@ 100mA - I

REG

SR087

100nF

10Ω, 3.0W

Wire Wound

470μF

200kΩ

510kΩ

510kΩ

FIGURE 3-6:

SR087 Additional Transient Protection. 

Maker
Microchip Technology Inc.