ST AN3339 Application note

AN3339

Application note

185 W power supply with PFC and standby supply for LED TV using the L6564, L6599A, and Viper27LN

Introduction

This document describes the characteristics and features of a 185 W, wide input mains range, power-factor-corrected, demonstration board for LED TV.

The architecture is based on a three-stage approach: a front-end PFC pre-regulator based on the L6564 TM PFC controller and a downstream LLC resonant half bridge converter using the L6599A resonant controller, delivering 12 V, 24 V, and 130 V. A flyback-based standby supply delivering 5 V, controlled by the Viper27LN, is also implemented. Thanks to the chipset used, the principal factors of this design are the very high efficiency as well as the very low input consumption during standby operation.

Figure 1. EVL185W-LEDTV: 185 W demonstration board

February 2011

Doc ID 18449 Rev 1

1/43

www.st.com

Contents	AN3339

Contents

1	Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . .	. 6
2	Efficiency measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
3	Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
4	Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
5	Thermal map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
6	Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . .	28
7	Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
8	PFC coil specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	36
9	Resonant power transformer specification . . . . . . . . . . . . . . . . . . . . .	38
10	Flyback transformer specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	40
11	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	42

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AN3339	List of tables

List of tables

Table 1. Overall efficiency measured at 230 Vac and 115 Vac mains voltage. . . . . . . . . . . . . . . . . 10 Table 2. Thermal maps reference points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Table 3. Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Table 4. PFC coil winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Table 5. Transformer winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Table 6. Transformer winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Table 7. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

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List of figures	AN3339

List of figures

Figure 1.	EVL185W-LEDTV: 185 W demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 1
Figure 2.	Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 9
Figure 3.	Standby power supply efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
Figure 4.	Standby consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
Figure 5.	EN61000-3-2 compliance at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 6.	JEITA-MITI compliance at 100 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 7.	EN61000-3-2 compliance at 230 Vac - 50 Hz, 75 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 8.	JEITA-MITI compliance at 100 Vac - 50 Hz, 75 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 9.	Standby supply waveforms at 115 Vac - 60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . .	13
Figure 10.	Standby supply waveforms at 230 Vac - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . .	13
Figure 11.	Standby supply waveforms at 400 Vdc, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
Figure 12.	Standby supply o/p rectifiers PIV at 400 Vdc, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
Figure 13.	Standby supply 5 V ripple at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
Figure 14.	Standby supply startup at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
Figure 15.	Standby supply burst mode at 230 Vac - 50 Hz, 10 mA load . . . . . . . . . . . . . . . . . . . . . . .	15
Figure 16.	Standby supply burst mode at 230 Vac, 10 mA load - detail . . . . . . . . . . . . . . . . . . . . . . .	15
Figure 17.	Standby supply OVP at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
Figure 18.	Standby supply OVP at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
Figure 19.	Standby supply OVP at 115 Vac - 60 Hz, 0.5 A load . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
Figure 20.	Standby supply OVP at 115 Vac, 0.5 A load - detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
Figure 21.	Standby supply o/p short-circuit at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . .	17
Figure 22.	Standby supply o/p short-circuit at 230 Vac, full load - detail . . . . . . . . . . . . . . . . . . . . . . .	17
Figure 23.	Standby supply dynamic load at 115 Vac - 60 Hz - PFC off. . . . . . . . . . . . . . . . . . . . . . . .	17
Figure 24.	Standby supply dynamic load at 115 Vac - 60 Hz - PFC on . . . . . . . . . . . . . . . . . . . . . . . .	17
Figure 25.	PFC Vds and inductor current at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . .	18
Figure 26.	PFC Vds and inductor current at 115 Vac, full load - detail . . . . . . . . . . . . . . . . . . . . . . . .	18
Figure 27.	PFC Vds and inductor current at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . .	19
Figure 28.	PFC Vds and inductor current at 230 Vac, full load - detail . . . . . . . . . . . . . . . . . . . . . . . .	19
Figure 29.	L6564 signals (1) at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
Figure 30.	L6564 signals (2) at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
Figure 31.	Resonant stage waveforms at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . .	20
Figure 32.	Resonant stage control signals at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . .	20
Figure 33.	12 V and 24 V rectifier PIV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
Figure 34.	130 V rectifier PIV. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
Figure 35.	Startup at full load and 115 Vac by on/off signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
Figure 36.	Shut down at full load and 115 Vac by on/off signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
Figure 37.	Startup at full load and 115 Vac by on/off signal - detail. . . . . . . . . . . . . . . . . . . . . . . . . . .	22
Figure 38.	12 V load transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
Figure 39.	24 V load transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
Figure 40.	130 V load transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
Figure 41.	24 V current limitation at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
Figure 42.	24 V short-circuit at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
Figure 43.	12 V short-circuit at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
Figure 44.	130 V short-circuit at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
Figure 45.	OVP at full load and 115 Vac on 24 V output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
Figure 46.	OVP at full load and 115 Vac on 12 V and 130 V outputs . . . . . . . . . . . . . . . . . . . . . . . . .	25
Figure 47.	Half cycle mains dip at full load and 115 Vac - 60 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
Figure 48.	Full cycle mains dip at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
Figure 49.	Thermal map at 115 Vac - 60 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26

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AN3339	List of figures

Figure 50. Thermal map at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 51. CE peak measurement at 115 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 52. CE peak measurement at 230 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 53. PFC coil electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Figure 54. PFC coil mechanical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Figure 55. Transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 56. Transformer overall drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Figure 57. Flyback transformer electrical diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Figure 58. Flyback transformer overall drawing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

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Main characteristics and circuit description	AN3339

1 Main characteristics and circuit description

The main features of the SMPS are:

●Universal input mains range: 90 ÷ 264 Vac - frequency 45 ÷ 65 Hz

●Output voltage 1: 130 V ±8 % at 620 mA for backlight

●Output voltage 2: 24 V ±8 % at 2 A for audio supply

●Output voltage 3: 12 V ±1 % at 4 A for panel supply

●Output voltage 4: 5 V ±2 % at 2 A for microprocessor supply

●Mains harmonics: acc. to EN61000-3-2 Class-D or JEITA-MITI Class-D

●Standby mains consumption: <170 mW at 230 Vac with 50 mW load

●Overall efficiency at full load: >90 %

●EMI: acc. to EN55022-Class-B

●Safety: acc. to EN60065

●Dimensions: 115x204 mm, 25 mm maximum component height from PCB

●PCB: single side, 70 µm, CEM-1, mixed PTH/SMT

The circuit is made up of two sections: a 10 W standby supply delivering 5 V, dedicated to supplying the microprocessor and the logic circuitry, and a bigger section made up of a front-end PFC and an LLC resonant converter delivering three output voltages, 12 V is dedicated to supplying the TV panel, 24 V to supplying the audio power amplifiers and 130 V is dedicated to the backlight.

The PFC stage delivers 400 V constant voltage and acts as the pre-regulator for both the LLC stage and the standby supply.

An external signal, referred to secondary ground, turns the PFC and the LLC stage on and off.

Startup

At turn-on the standby supply begins startup and delivers 5 V dedicated to the TV microprocessor and other logic circuitry. It also generates the auxiliary voltage powering the PFC and LLC controllers at primary side via the linear regulator Q7. Q7 is activated by the optocoupler U5 that is driven by the logic signal on/off. At startup, the on/off signal (active high) from the microprocessor is supposed to be low, so the PFC and the LLC do not work.

Once the on/off signal is asserted high, the regulator Q7 delivers 14 V powering the PFC controller L6564 and the LLC controller L6599A; to always ensure proper operation of the LLC, the circuit is designed so that the PFC starts first, then the downstream converter. The LINE pin of L6599A allows the resonant stage to operate only if the PFC output is delivering its rated output voltage. It prevents the resonant converter from working with too low input voltage that can cause undesirable capacitive mode operation.

The L6599A LINE pin internal comparator has a hysteresis which allows to independently set the turn-on and turn-off voltage. The LLC turn-on voltage (PFC output) has been set to 380 V while the turn-off threshold has been set to 300 V. This last value avoids capacitive mode operation by the LLC stage but allows the resonant stage to operate even in the case of mains sag and consequent lowering of PFC output voltage.

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AN3339	Main characteristics and circuit description

Brownout protection

Brownout protection prevents the circuit from working with abnormal mains levels. It is achieved by two separate circuits, one using the brownout pin of the Viper and a second using an internal comparator of the L6564 dedicated to this function: this pin is internally connected to the VFF pin (#5) providing the information of the mains voltage peak value. The internal comparator allows the IC operations if the mains level is correct, within the nominal limits.

If the input voltage is below ~80 Vac (typ.), circuit startup is not allowed.

Resonant power stage

The downstream converter featuring the ST L6599A, incorporates all the functions necessary to properly drive the resonant converter with a 50 % fixed duty cycle and works with variable frequency.

The transformer, using the integrated magnetic approach and incorporating the resonant series inductance, delivers 3 output voltages without any post-regulator.

The transformer configuration chosen for the secondary winding delivering 12 V and 24 V output is center-tap and makes use of power Schottky rectifiers. For the secondary winding delivering 130 V, a full bridge configuration using four ultrafast diodes has been chosen. A small LC filter has been added on each output, to filter the high frequency ripple.

Output voltage feedback loop

The resonant stage feedback loop is implemented by means of a typical circuit using a TL431 modulating the current in the optocoupler diode. The three outputs are regulated by a weighted feedback control.

On the primary side, R37 - connecting the RFMIN pin (#4) to the optocoupler's phototransistor - closes the feedback loop and its value sets the maximum switching frequency. R36, connecting the same pin to ground, sets the minimum switching frequency. The RC series R22 and C21 sets both soft-start maximum frequency and duration.

L6599A overload and short-circuit protection

The current into the primary winding is sensed by the loss-less circuit R53, C36, D14, D12, R55, and C38, and is fed into the ISEN pin (#6). In the case of overcurrent, the voltage on the pin overpass the internal comparator threshold (0.8 V), triggering a protection sequence. The capacitor (C37) connected to the DELAY pin (#2) is charged by an internal 150 µA current generator and is slowly discharged by the resistor R54. This pin is connected to the DIS pin and as soon as the voltage achieves 1.85 V, the IC stops switching latched. On/off signal recycling is necessary to restart the resonant converter.

Overvoltage and open loop protection

Both PFC and resonant stages are equipped with their own overvoltage protection.

The PFC controller L6564 monitors its output voltage via the resistor divider connected to the PFC_OK pin (#6) protecting the circuit in case of loop failures, disconnection, or deviation from the nominal value of the feedback loop divider. When a fault condition is detected, by monitoring both PFC_OK and INV pins, the PFC_OK circuitry latches the L6564 operations. The PFC is kept latched until the mains voltage is recycled.

In the case of overvoltage by the resonant stage the Zener diodes D16, D17, and D29 detect the output voltages and conduct. This causes Q10 to turn on and, consequently, Q9

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Main characteristics and circuit description	AN3339

also turns on. These two transistors form an SCR structure that shorts to ground the anode of the U5 optocoupler in case of an overvoltage event. In this way, Q7 cannot deliver supply voltage Vcc to the controller which remains latched until the mains voltage is recycled.

To protect the PFC and LLC controllers from being powered with an abnormal voltage, which may occur in the case of a failure of the regulator based on Q7, an overvoltage protection is provided by the Zener diode D13. In the case of the Q7 regulator providing an excessive output voltage, D13 is reverse-biased and latches the L6599A through the DIS pin (#8).

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Efficiency measurement	AN3339

2 Efficiency measurement

Table 1 and 2 show the overall efficiency, measured at both nominal mains voltages. At 230 Vac the full load efficiency is 93.3 % and at 115 Vac it is 90.8 %. Average efficiency measured at 25 %, 50 %, 75 %, and 100 % of nominal load is higher than 90 %.

The average efficiency has been calculated according to ENERGY STAR® 2.0 criteria. Results are summarized in the following figures.

Table 1.	Overall efficiency measured at 230 Vac and 115 Vac mains voltage
							230 V - 50 Hz
Test		12 V		24 V		130 V			5 V		Pout[W]	Pin[W]	Eff.[%]
		Vout	Iout	Vout	Iout	Vout	Iout	Vout		Iout
		[V]	[A]	[V]	[A]	[V]	[A]	[V]		[A]
25 % load eff.		11.95	1.00	24.19	0.50	128.89	0.15	5.05		0.50	46.09	52.00	88.6
50 % load eff.		11.93	2.01	24.28	1.00	129.95	0.31	5.04		1.00	93.30	101.50	91.9
75 % load eff.		11.90	3.01	24.38	1.50	131.05	0.47	5.04		1.50	141.67	151.90	93.3
100 % load eff.		11.88	3.99	24.48	2.00	132.18	0.62	5.04		2.00	187.96	201.50	93.3
Average eff.													91.8
							115 V - 60 Hz
Test		12 V		24 V		130 V			5 V		Pout[W]	Pin[W]	Eff.[%]
		Vout	Iout	Vout	Iout	Vout	Iout	Vout		Iout
		[V]	[A]	[V]	[A]	[V]	[A]	[V]		[A]
25 % load eff.		11.95	1.00	24.19	0.50	128.89	0.15	5.05		0.50	46.09	52.35	88.0
50 % load eff.		11.93	2.01	24.28	1.00	129.95	0.31	5.04		1.00	93.30	102.85	90.7
75 % load eff.		11.90	3.01	24.38	1.50	131.05	0.47	5.04		1.50	141.67	154.92	91.4
100 % load eff.		11.87	3.99	24.47	2.00	132.15	0.62	5.04		2.00	187.76	206.84	90.8
Average eff.													90.2

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Doc ID 18449 Rev 1

AN3339	Efficiency measurement

Standby supply efficiency

Standby power supply efficiency has been measured and the results are plotted in Figure 3. As shown, the efficiency during rated load operation is better than 82 %, at both nominal mains voltages from 50 % to full load.

Figure 4 shows consumption at very light load, such as microprocessor and wake-up circuitry. This measurement is representative of the significant low consumption from the mains required for microprocessor powering. It should be mentioned that the standby supply efficiency has been calculated measuring the input power at the input connector, including power loss contribution due to all residual loads connected to mains before and after the input bridge rectifier, such as the EMI filter and PFC dividers.

Figure 3. Standby power supply efficiency

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Figure 4. Standby consumption

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Doc ID 18449 Rev 1

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Harmonic content measurement	AN3339

3 Harmonic content measurement

The main purpose of a PFC pre-regulator is the input current shaping to reduce the harmonic content below the limits of the relevant regulations. This demonstration board has been tested according to the European standard EN61000-3-2 Class-D and Japanese standard JEITA-MITI Class-D, at full load and 75 W input power.

Figure 5, 6, 7, and 8 show the test results. As can be seen, the PFC is able to reduce the harmonics well below the limits of both regulations in all conditions. Total harmonic distortion (THD) and power factor (PF) values are given below each diagram.

Figure 5.				EN61000-3-2 compliance at																				Figure 6. JEITA-MITI compliance at
				230 Vac - 50 Hz, full load																								100 Vac - 50 Hz, full load
			Measured Value						EN61000-3-2 Class-D Limits																		Measured Value							JEITA-MITI Class-D Limits
	10																								10
[A]	1																							[A]	1
Current	0.1																							Current	0.1
Harmonic	0.01																							Harmonic	0.01
	0.001																								0.001
	0.0001																								0.0001
	1		3	5	7	9	11	13	15	17	19	21	23	25	27		29	31	33	35	37	39			1		3	5	7	9	11	13	15	17	19	21		23	25	27	29	31	33	35	37	39
									Harmonic Order [n]																								Harmonic Order [n]
																				AM08372v1																								AM08373v1
Vin=230 Vac - 50 Hz, Pin=204 W																								Vin=100 Vac - 50 Hz, Pin=209 W
THD=4.22 %, PF=0.985																								THD=3.71 %, PF=0.999

Figure 7. EN61000-3-2 compliance at																							Figure 8. JEITA-MITI compliance at
				230 Vac - 50 Hz, 75 W																							100 Vac - 50 Hz, 75 W
			Measured Value						EN61000-3-2 Class-D Limits																	Measured Value							JEITA-MITI Class-D Limits
	10																							10
[A]	1																						[A]	1
Current	0.1																						Current	0.1
Harmonic	0.01																						Harmonic	0.01
	0.001																							0.001
	0.0001																							0.0001
	1		3	5	7	9	11	13	15	17	19	21	23	25	27	29	31	33	35	37	39			1		3	5	7	9	11	13	15	17	19	21	23	25	27	29	31	33	35	37	39
									Harmonic Order [n]																							Harmonic Order [n]
																			AM08374v1																							AM08375v1
Vin=230 Vac - 50 Hz, Pin=75 W																							Vin=100 Vac - 50 Hz, Pin=75 W
THD=7.29 %, PF=0.867																							THD=5.72% , PF=0.999

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Doc ID 18449 Rev 1

AN3339	Functional check

4 Functional check

Standby supply

In Figure 9 and 10 some waveforms of the standby supply under rated load operation are reported. It is based on the Viper27LN, a device integrating the controller and MOSFET in a single DIP-7 package. The Viper27LN works with fixed switching frequency at about 60 kHz, with frequency jittering to reduce EMI. In order to obtain a good efficiency and to reduce transformer size the converter has been designed to operate in continuous conduction mode at low mains (Figure 9) and discontinuous conduction mode at high mains (Figure 10) if PFC and resonant are not working.

Figure 9. Standby supply waveforms	Figure 10. Standby supply waveforms
at 115 Vac - 60 Hz - full load	at 230 Vac - 50 Hz - full load

CH1:	DRAIN (pin #8)	CH2: VDD (pin #2)	CH1:	DRAIN (pin #8)	CH2: VDD (pin #2)
CH3:	CONT (pin #3)	CH4: FB (pin #4)	CH3:	CONT (pin #3)	CH4: FB (pin #4)

In Figure 11 the converter waveforms are captured once the PFC is working. The small value of the standby transformer leakage inductance allows limited dissipation on the clamping network across the primary winding. In addition, the drain peak voltage is well below the Viper27LN rating even with maximum input voltage and full load operation.

Waveforms relevant to the secondary side are represented in Figure 12: the maximum reverse voltages applied to the rectifier are well below the component maximum ratings.

Doc ID 18449 Rev 1

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