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Old 19th June 2015, 12:54 AM   #1
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Default Half-Bridge SMPS with PFC

Hi! I'm starting to build a 350W Half-Bridge SMPS with a PFC stage using the UCC28019A from Texas Instruments. I've built other Half-Bridge SMPS with the two input capacitor forming a voltage divider. The problem is that now I don't have the voltage divider I only have 390VDC from the PFC. How do I connect the MOSFETs now?

Searching over internet I found this design that uses only one MOSFET connected to one end of the primary and the other end connected directly to the PFC output. Also this on page 3 it uses 2 MOSFETs one connected to each end of the primary with the diodes D8 and D9 that are used to clamp high voltage spikes I think. And finally this using 2 MOSFETs with the blocking capacitor but this is a ZVS Half-Bridge and I want a hard-switching Half-Bridge.

What's the correct way to connect it? Are this topologies still Half-Bridge when using just one MOSFET and no blocking cap?
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Old 19th June 2015, 06:39 AM   #2
Elvee is offline Elvee  Belgium
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Just use a capacitive half-bridge:


Click the image to open in full size.
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Old 19th June 2015, 07:18 AM   #3
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Quote:
Originally Posted by dragondgold View Post
Hi! I'm starting to build a 350W Half-Bridge SMPS with a PFC stage using the UCC28019A from Texas Instruments. I've built other Half-Bridge SMPS with the two input capacitor forming a voltage divider. The problem is that now I don't have the voltage divider I only have 390VDC from the PFC. How do I connect the MOSFETs now?
The PFC-output feeds VCC, capacitors stay at the same position and everything is fine
Quote:
Originally Posted by dragondgold View Post
Searching over internet I found this design that uses only one MOSFET connected to one end of the primary and the other end connected directly to the PFC output. Also this on page 3 it uses 2 MOSFETs one connected to each end of the primary with the diodes D8 and D9 that are used to clamp high voltage spikes I think. And finally this using 2 MOSFETs with the blocking capacitor but this is a ZVS Half-Bridge and I want a hard-switching Half-Bridge.

What's the correct way to connect it? Are this topologies still Half-Bridge when using just one MOSFET and no blocking cap?
Your link points to a one transistor forward converter - this is a totally different beast to your half-bridge.

Why do you prefer hard-switching? This is imho an obsolete concept with many disadvantages compared to LLC converters.

And last but not least - did you ever wind a ferrite transformer that delivers 350W of continuous output power without generating excessive heat?
I did, but it took a long learning curve.
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Old 19th June 2015, 05:42 PM   #4
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Quote:
Originally Posted by Elvee View Post
Just use a capacitive half-bridge:


Click the image to open in full size.
Do I still need big capacitors in order to reduce the ripple? Or I can use small ones just to form the divider?

Quote:
Originally Posted by voltwide View Post
The PFC-output feeds VCC, capacitors stay at the same position and everything is fine


Your link points to a one transistor forward converter - this is a totally different beast to your half-bridge.

Why do you prefer hard-switching? This is imho an obsolete concept with many disadvantages compared to LLC converters.

And last but not least - did you ever wind a ferrite transformer that delivers 350W of continuous output power without generating excessive heat?
I did, but it took a long learning curve.
Because it's simpler than LLC converters but I would like to try to make one. Do you recommend any book to read about them? Specifically about a Half-Bridge LLC Converter?

Yes, I have a Half-Bridge SMPS providing 300W of continuos output power. It generates some heat but nothing excessive.

If someone can recommend some book to learn to design LLC converters that would be great!
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Old 19th June 2015, 06:16 PM   #5
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I found these helpful:
http://www.st.com/web/en/resource/te...CD00174208.pdf
http://u.dianyuan.com/bbs/u/46/1161681433.pdf
but there are loads of technical papers dealing with LLC on the internet
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Old 19th June 2015, 07:09 PM   #6
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Quote:
Originally Posted by voltwide View Post
I found these helpful:
http://www.st.com/web/en/resource/te...CD00174208.pdf
http://u.dianyuan.com/bbs/u/46/1161681433.pdf
but there are loads of technical papers dealing with LLC on the internet
I've read about resonant converters in the Pressman Book and it says they are not suitable when the output load varies too much. This SMPS is intended to have a wide range of output load from maybe 100-200mA up to 7-8A. Is this possible with resonant converters or is just something you can't avoid with them?
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Old 19th June 2015, 07:11 PM   #7
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I have designed LLC resonant converters and not found a problem with different loads except they need a small residual current. I did this by putting a resistor across the output.
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Old 20th June 2015, 01:26 AM   #8
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Quote:
Originally Posted by nigelwright7557 View Post
I have designed LLC resonant converters and not found a problem with different loads except they need a small residual current. I did this by putting a resistor across the output.
Do you have any paper or book to guide me in the design of a LLC converter? I've read the PDFs from voltwide about how this converter works but now I would need something to help me to calculate the resonant elements and design considerations.
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Old 20th June 2015, 01:33 AM   #9
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I did it very much by feel.

I used a PIC micro to generate the frequencies into a IR2113 gate driver.
Depending on the feedback signal I output one of two frequencies.
One that was just above resonance and the other well above resonance.
I used 14 primary turns on inductor and 4 output turn's
The output from the mosfets was fed through two 100nf capacitors in parallel into the primary of the inductor.

I did quite a bit of experimentation and found a useful thing was to put a 0r1 in series with lower mosfet to monitor current. I then adjusted resonant frequency to give max current without blowing fuses.

Here is the PIC code.

;inth0.ASM
;**********
#include p16f506.inc
LIST R=DEC
; LIST

;----- CONFIG Options --------------------------------------------------
;_OSC_LP EQU H'0FF8' ; LP oscillator and 18 ms DRT
;_LP_OSC EQU H'0FF8' ; LP oscillator and 18 ms DRT
;_OSC_XT EQU H'0FF9' ; XT oscillator and 18 ms DRT
;_XT_OSC EQU H'0FF9' ; XT oscillator and 18 ms DRT
;_OSC_HS EQU H'0FFA' ; HS oscillator and 18 ms DRT
;_HS_OSC EQU H'0FFA' ; HS oscillator and 18 ms DRT
;_OSC_EC EQU H'0FFB' ; EC Osc With RB4 and 1.125 ms DRT
;_EC_OSC EQU H'0FFB' ; EC Osc With RB4 and 1.125 ms DRT
;_OSC_IntRC_RB4EN EQU H'0FFC' ; INTRC With RB4 and 1.125 ms DRT
;_IntRC_OSC_RB4EN EQU H'0FFC' ; INTRC With RB4 and 1.125 ms DRT
;_OSC_IntRC_CLKOUTEN EQU H'0FFD' ; INTRC With CLKOUT and 1.125 ms DRT
;_IntRC_OSC_CLKOUTEN EQU H'0FFD' ; INTRC With CLKOUT and 1.125 ms DRT
;_OSC_ExtRC_RB4EN EQU H'0FFE' ; EXTRC With RB4 and 1.125 ms DRT
;_ExtRC_OSC_RB4EN EQU H'0FFE' ; EXTRC With RB4 and 1.125 ms DRT
;_OSC_ExtRC_CLKOUTEN EQU H'0FFF' ; EXTRC With CLKOUT and 1.125 ms DRT
;_ExtRC_OSC_CLKOUTEN EQU H'0FFF' ; EXTRC With CLKOUT and 1.125 ms DRT

;_WDT_OFF EQU H'0FF7' ; WDT disabled
;_WDT_ON EQU H'0FFF' ; WDT enabled

;_CP_ON EQU H'0FEF' ; Code protection on
;_CP_OFF EQU H'0FFF' ; Code protection off

;_MCLRE_OFF EQU H'0FDF' ; RB3/MCLR pin functions as RB3, MCLR tied internally to VDD
;_MCLRE_ON EQU H'0FFF' ; RB3/MCLR pin functions as MCLR

;_IOSCFS_OFF EQU H'0FBF' ; 4 MHz INTOSC Speed
;_IOSCFS_ON EQU H'0FFF' ; 8 MHz INTOSC Speed


;20MHZ
__CONFIG _MCLRE_OFF & _WDT_ON & _CP_OFF & _OSC_HS

;*****************************************
;SUBWF FLAGS
;IF W > MEM THEN NC
;IF W = MEM THEN C
;IF W < MEM THEN C
;IF W<= MEM THEN C

;IF MEM>=W THEN C
;IF MEM<W THEN NC
;*****************************************
#DEFINE SET0 1
#DEFINE SET1 2
#DEFINE SET2 4
#DEFINE SET3 8
#DEFINE SET4 16
#DEFINE SET5 32
#DEFINE SET6 64
#DEFINE SET7 128

#DEFINE LED PORTB,0
#DEFINE OPTOINPUT PORTB,1
#DEFINE NOTOVERCURRENT PORTB,2

;PORTC = GATES

FIRSTRAM EQU 0XD ;16F506 RAM START ADDRESS

;10H TO 1FH IN BANK 0
CBLOCK FIRSTRAM
TEMP
TEMP1
TEMP2
TEMPL
TEMPM
PULSES
ENDC

ORG 0
INCLUDE MACRO.ASM
CLRWDT
CLRF FSR ;BANK 0 RAM

MOVWF OSCCAL ;SET UP OSC FREQ ACCURATELY

MOVLW 0X30 ;A2D ALL OFF
MOVWF ADCON0

CLRF PORTC ;ALL MOSFETS OFF
MOVLW 0
TRIS PORTC

CLRF PORTB ;LED OFF
MOVLW SET1+SET2 ; OPTO AND NOTOVERCURRENT ARE INPUTS
TRIS PORTB

MOVLW 0X41 ;COMPARATORS OFF
MOVWF CM1CON0
MOVWF CM2CON0

CLRF VRCON

MOVLW 0XC0 ;DISABLE WEAK PULL UPS ON PORTB
OPTION

;WAIT 4 SECS TO LET POWER SUPPLY CAPS CHARGE UP
MOVLW 4
CALL WAITWSECONDS

;**********
;SOFT START
;**********
RESTART
MOVLW 0
MOVWF TEMPL
MOVLW 20 ;20ms
MOVWF TEMPM

SOFTSTART ;166KHz 30 cycle loop

MOVLW 1
CLRF PORTC ;DEADTIME
NOP ;DEADTIME
MOVWF PORTC
;HAVE TO IGNORE OVER CURRENT HERE as s/c to start with
CLRWDT
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
MOVLW 2
CLRF PORTC ;DEADTIME
NOP ;DEADTIME
MOVWF PORTC
;;;;;;;;
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
DECFSZ TEMPL,F
GOTO SOFTSTART

DECFSZ TEMPM,F
GOTO SOFTSTART

;*************************************************
;based on 30uh leakage inductance Lr, Lm =155uH and 200nf Cr
;*************************************************
ON BSF LED ;POWERED UP OK

MLOOP
BTFSC OPTOINPUT
GOTO SLOWCLOCK ;GO IF OPTO HIGH (VOLTS TOO LOW)
;;;;;;;;;;;;;;;;;;;;;;;;;;
;FASTCLOCK
; 166KHZ 2 * 15 CYCLE LOOP
FASTCLOCK
CLRF PORTC ;DEADTIME
MOVLW 1 ;DEADTIME
MOVWF PORTC
;;;;;;;;;;;;
CLRWDT ;LET SETTLE 800ns
NOP
NOP
NOP
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
CLRF PORTC ;DEADTIME
MOVLW 2 ;DEADTIME
MOVWF PORTC
;;;;;;;;;;;;
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
GOTO MLOOP
;*************************
;125KHZ 2* 20 CYCLE LOOP
SLOWCLOCK
CLRF PORTC ;DEADTIME
MOVLW 1 ;DEADTIME
MOVWF PORTC
;;;;;;;;;;;;
CLRWDT ;LET SETTLE 800nS
NOP
NOP
NOP
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
BTFSS NOTOVERCURRENT ;GO IF OVER CURRENT
GOTO BROKEN
NOP
CLRF PORTC ;DEADTIME
MOVLW 2 ;DEADTIME
MOVWF PORTC

;;;;;;;;;;;;
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
GOTO MLOOP
;************************
;SLOW FLASH LED
BROKEN CLRF PORTC ;MOSFETS OFF
BSF LED
CALL WAIT250MS
CALL WAIT250MS
CALL WAIT250MS
CALL WAIT250MS
BCF LED
CALL WAIT250MS
CALL WAIT250MS
CALL WAIT250MS
CALL WAIT250MS
GOTO BROKEN
;******************************************
;FAST FLASH LED
BROKENSOFT CLRF PORTC ;MOSFETS OFF
BSF LED
CALL WAIT250MS
BCF LED
CALL WAIT250MS
GOTO BROKENSOFT
;******************************************
;63 max input
WAITWSECONDS MOVWF TEMP2
CLRC
RLF TEMP2,F ;*2
RLF TEMP2,W ;*4

GOTO SECS

WAIT1SECOND

MOVLW 4
SECS MOVWF TEMP2
L3
MOVLW 250 ;250MS LOOP
MOVWF TEMP1
L2
MOVLW 250 ;1 MS LOOP
MOVWF TEMP
L1 CLRWDT ;10 CYCLE LOOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
DECFSZ TEMP,F
GOTO L1

DECFSZ TEMP1,F
GOTO L2

DECFSZ TEMP2,F
GOTO L3
RETLW 0
;************************************
WAIT1MS MOVLW 250
MOVWF TEMP
W1M CLRWDT ;20 CYCLE LOOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
DECFSZ TEMP,F
GOTO W1M
RETLW 0
;***********************************
WAIT250MS MOVLW 250
MOVWF TEMP2
W2M CALL WAIT1MS
DECFSZ TEMP2,F
GOTO W2M
RETLW 0
;*************************************
WAIT50MS MOVLW 50
MOVWF TEMP2
W2M50 CALL WAIT1MS
DECFSZ TEMP2,F
GOTO W2M50
RETLW 0
;*************************************
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Last edited by nigelwright7557; 20th June 2015 at 01:44 AM.
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Old 20th June 2015, 01:47 AM   #10
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Quote:
Originally Posted by dragondgold View Post
Do you have any paper or book to guide me in the design of a LLC converter? I've read the PDFs from voltwide about how this converter works but now I would need something to help me to calculate the resonant elements and design considerations.
Look up the IRS27951 SMPS IC application notes.
That goes through the design process.
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