HT7A6312 Low Cost Power Supply in Non-isolation Flyback Configuration

AN0371E V1.10 1 / 10 March 1, 2018

HT7A6312 Low Cost Power Supply in Non-isolation Flyback Configuration

D/N：AN0371E

Features

This switching power device has a non-isolated buck architecture and has the following

features:

• Wide operating voltage range

• Few external component requirements

• Under conditions of no-load the input power consumption is lower than 200mW

• Over temperature protection and output short circuit protection

Typical System Characteristics

Parameter Wide Range (90VAC ~ 265VAC)

Input AC Frequency 47Hz~63Hz

Output voltage (VOUT1、VOUT2) 18VDC /5VDC

Output current (IOUT1、IOUT2) 300mA(max)/ 50mA(max)

Efficiency >71%@230VAC

Standby Power Consumption <0.2W@230VAC

Output Short Circuit Power Consumption <0.7W@230VAC

Output Short Circuit Protection Yes

Over Temperature Protection Yes

HT7A6312 Low Cost Power Supply in Non-isolation Flyback Configuration

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Application Circuit and Component List

U1

D6

18V

R1

R2EC1 C1

T1

EC2

C2

Z1

ACIN CX1

VSS

FB

VCC

SW

SW

SW

SW

VSS

1

2

3

4

8

7

6

5

F1

D1 D3

D2 D4

D9

GNDVIN VOUT

D7

D8

18V

U2

EC3

EC4 EC5

5V

D5

C3

Rfb

Component Package Parameter Manufacturer

C1 DIP 1nF/1KV

C2 DIP CE 22nF/50V

C3 DIP CE 100nF/50V

CX1 DIP 0.1µF/275Vac

D1,D2,D3,D4,D6,D9 DO-41 1N4007, 1KV/1A

D5 Jump Wire

D7, D8 DO-41 UF4007

EC1 DIP EL 4.7µF/400V

EC2 DIP EL 2.2µF/50V

EC3, EC4, EC5 DIP EL 100µF/25V

F1 DIP 1A/250Vac

R1 Jump Wire

R2 DIP 51KΩ, 1W

Rfb SMD0603 RES 100

T1 EE16 EE16, 2.8mH

U1 DIP8 HT7A6312 HOLTEK

U2 TO-92 78L05

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System Board Introduction

Top View

Bottom View

Functional Description The HT7A6312 is a highly functionally integrated device which uses an integrated PWM

controller with current mode control to drive an integrated high voltage power MOSFET.

Users can use either an isolated or non-isolated type architecture for system control

according to their requirements. In the isolated type architecture, the output signal is

transmitted to the primary side through a photo-coupler. However in the non-isolated

architecture, the input side and the output side use the same ground. The output signal is

directly sent back to the HT7A6312 to implement the output voltage driving. In addition, the

HT7A6312 operates with an excellent low standby current and uses a Burst Mode function

to achieve a low system standby power consumption.

The HT7A6312 contains several system protection functions, such as output short circuit

protection, IC over voltage protection and over temperature protection, etc. which ensure

that the system operates safely and with higher reliability.

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Pin Description

• VSS The VSS pin is the power MOSFET source and the IC ground reference.

• FB This is the feedback input pin. It defines the peak inductor current that can pass through the integrated MOSFET. When the logic signal on the FB pin is “0”, it corresponds to the maximum peak inductor current. An FB resistor with the resistance of 100Ω is connected to prevent from aging and strengthen the reliability of operations in hostile environment.

• VCC The VCC pin is designed with a UVLO function. When the VCC voltage exceeds 14.5V (typ.), the HT7A6312 will start operation. When the VCC voltage is lower than 8V (typ.), the HT7A6312 will be turned off.

• SW The SW pin is connected to the drain of the integrated MOSFET. It is also used as the input pin for the internal high voltage start up JFET.

Transformer Design

• The T1 transformer specifications are as follows:

Test Data Test Condition: Room Temperature

AC input voltage range: 180VAC ~265VAC，I18V is 0A~300mA(max)，I5V is 0A~50mA(max)

The AC input power consumption is for a no-load condition:

VAC(V) 180 200 220 240 265 Pin(W) 0.564 0.324 0.192 0.155 0.134 18VOUT(V) 18.72 18.72 18.7 18.71 18.7 5VOUT (V) 5.03 5.03 5.03 5.03 5.03 I18V(mA) 0 I5V(mA) 0

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System efficiency with different load conditions:

230VAC

18Vout(V) 18.76 18.72 18.69 18.66 18.65 18.61 18.58 18.55 18.46 18.33

I18V(mA) 10.03 20.08 30.15 40.05 50.1 60.15 80.1 100.06 200.15 300.07

5Vout(V) 5.03 5.03 5.03 5.03 5.03 5.03 5.03 5.03 5.03 5.03

I5V(mA) 0 0 0 0 0 0 0 0 0 0

Pin(W) 0.787 1.055 1.261 1.4719 1.685 1.9 2.401 2.8758 5.1819 7.469

η(%) 23.9 35.63 44.68 50.77 55.45 58.91 61.98 64.54 71.3 73.64

18Vout(V) 18.73 18.7 18.66 18.64 18.62 18.62 18.56 18.55 18.45 18.28

I18V(mA) 10.1 20.08 30.15 40.05 50.1 60.15 80.11 100.06 200.15 300.09

5Vout(V) 5.05 5.05 5.05 5.05 5.05 5.05 5.05 5.05 5.05 5.05

I5V(mA) 25.05 25.05 25.05 25.05 25.05 25.05 25.05 25.05 25.05 25.05

Pin(W) 1.0919 1.303 1.518 1.726 1.943 2.208 2.7028 3.183 5.465 7.74

η(%) 28.91 38.52 45.39 50.58 54.52 56.45 59.69 62.28 69.88 72.5

18Vout(V) 18.71 18.66 18.65 18.64 18.63 18.59 18.55 18.57 18.42 18.3

I18V(mA) 10.1 20.08 30.15 40.05 50.1 60.15 80.11 100.06 200.15 300.09

5Vout(V) 5.06 5.06 5.06 5.06 5.06 5.06 5.06 5.06 5.06 5.07

I5V(mA) 50.1 50.1 50.1 50.1 50.1 50.1 50.1 50.1 50.1 50.1

Pin(W) 1.343 1.558 1.772 1.986 2.242 2.486 2.974 3.494 5.7398 8.001

η(%) 32.94 40.28 46.03 50.35 52.93 55.17 58.49 60.43 68.64 71.81

AC input Power Consumption (No-load)

AC input Power Consumption (Output Short Circuit)

Standby Power

0

0.1

0.2

0.3

0.4

0.5

0.6

180 200 220 240 265Vac(V)

Pin

(W)

Pin(W) at Output Short

0

0.2

0.4

0.6

0.8

1

180 230 265Vac(V)

Pin

(W)

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System Efficiency (230VAC, Different Load Conditions)

18VOUT Output Voltage Stability (230VAC, 5VOUT Different Load Conditions)

SW Pin Voltage Waveform (230VAC, No-load Output)

Efficiency

0102030405060708090

100

10 20 30 40 50 60 80 100 200 30018V Output Current (mA)

Effi

cien

cy (%

)

I5V=0mAI5V=25mAI5V=50mA

18Vout vs. I5Vout

18

18.2

18.4

18.6

18.8

19

10 20 30 40 50 60 80 100 200 300

I18Vout(mA)

18V

out(V

)

I5V=0mAI5V=25mAI5V=50mA

HT7A6312 Low Cost Power Supply in Non-isolation Flyback Configuration

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SW Pin Voltage Waveform (230VAC, Full-load Output)

SW Pin Voltage Waveform (230VAC, Output Short Circuit)

Output Voltage Ripple (230VAC)

HT7A6312 Low Cost Power Supply in Non-isolation Flyback Configuration

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Voltage Ripple (230VAC, Load-variant Output) (a)

Voltage Ripple (230VAC, Load-variant Output) (b)

Output Voltage Waveform (230VAC, No-load Start Up)

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Output Voltage Waveform (230VAC, Full-load Start Up)

Versions and Revision

Date Author Issue and Revision Note

2015.03.06 詹作晟 V1.00, First version.

2018.02.12 陳佳宏 Version 1.10 updated contents: 1. Application Circuit and Component List 2. The figures and FB pin description of the System

Board Introduction section.

Reference Files

Reference file: HT7A6312 Data Sheet.

For more information, refer to the Holtek official website www.holtek.com.

HT7A6312 Low Cost Power Supply in Non-isolation Flyback Configuration

AN0371E V1.10 10 / 10 March 1, 2018

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