ST AN3358 Application note

AN3358

Application note

Turbo2 600 V diodes:

optimized solutions for PFC and other applications

Introduction

In a switched mode power supply, there are a great number of electronic functions where
600 V ultrafast diodes are used. Each diode has a specific function. In one application a
parameter can be critical but secondary in another.

A rectifier manufacturer who wants to propose an optimized solution for each function needs
to develop several families with different trade-offs (mainly between the forward voltage V
and reverse recovery charge Q

STMicroelectronics’ Turbo2 600 V ultrafast diodes offer three different families in order to
offer an optimal solution for each application.

After some general information about this new technology, a discussion of the PFC
application, working in continuous mode, transition mode and fixed-off-time, is presented. In
the case of continuous mode operation, hard switching and soft switching conditions are
considered. Some other conventional functions are also touched upon.

).

rr

F

September 2011 Doc ID 018581 Rev 1 1/18

www.st.com

Contents AN3358

Contents

1 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Technology information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 V

1.3 Platinum doping and low leakage current . . . . . . . . . . . . . . . . . . . . . . . . . 3

, Qrr trade-off for the three families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

F

2 Main applications of 600 V ultrafast diodes . . . . . . . . . . . . . . . . . . . . . . 5

2.1 Power factor corrector applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.1 Boost diode in PFC working in continuous mode . . . . . . . . . . . . . . . . . . 5

2.1.2 Boost diode in PFC working in transition mode . . . . . . . . . . . . . . . . . . . 10

2.1.3 Boost diode working in fixed-off-time (FOT) PFC . . . . . . . . . . . . . . . . . 12

2.2 Other applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

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AN3358 General information

1 General information

1.1 Technology information

The Turbo2 families are manufactured using simple rules to insure high quality and
reliability. These diodes are planar structures on epitaxial layers. The wafers are thus
subjected to reduced mechanical stress for planar diodes compared to mesa ones.

The use of epitaxial layers makes the V

trade-off independent of the wafer thickness, the

F/trr

contrary of homogenous diodes. These properties make the manufacturing of large
diameter wafers possible. So the wafers benefit from state-of-the-art technology on recent
equipment.

Epitaxial diodes, which present good drift area thickness, are particularly suitable for diodes
up to 600 V and exhibit a significantly superior V

trade-off. The lifetime control of the

F/trr

carriers for the Turbo2 diodes is obtained through platinum (P
for high junction temperature applications because it results in low reverse current at
elevated temperature and, in this way, presents a low thermal runaway risk.

1.2 VF, Qrr trade-off for the three families

The three families are: STTHxxR06 (R stands for rapid with low Qrr), STTHxx06 (medium VF
and Q

Figure 1 shows where a trade-off occurs in three operational areas. A technology using gold

doping is also shown.

Figure 1. V

), and STTHxxL06 (Low forward voltage).

rr

- Qrr trade-off for an 8 A diode

F

V (V)

F

1.7

Typical values

) doping. Pt doping is required

t

IF= 8 A
VR= 400 V
dIF/dt = 200 A/µs
Tj= 125 °C

R Family

1.2

Medium Family

Platinum doping

0.7
0 200 400 600 800 1000 1200 1400 1600

Gold doping

L Family

Qrr(nC)

1.3 Platinum doping and low leakage current

Figure 2 shows the trade-off between leakage current IR and Q

areas. The faster the diode, the higher the I
doping. For the same Q

, IR is approximately 100 times lower with platinum doping. The

rr

corresponding “R” family with gold doping would have a high maximum leakage current
(18 mA at 125 °C and 400 V). As shown later in this Application note, with such a leakage
current thermal instability can be reached for operating junction temperatures higher than
125 °C in a conventional application.

Doc ID 018581 Rev 1 3/18

is. This rule is true for both gold and platinum

R

in several operational

rr

General information AN3358

1

10

100

1000

10000

100000

0 500 1000 1500 2000

It will also be shown that IR is also a critical parameter for diodes in axial and SMD
packages.

Figure 2. I

- Qrr trade-off in several operational areas for an 8 A diode

R

I (µA)

Rmax

IF= 8 A
VR= 400 V
dIF/dt = 200 A/µs
Tj= 125 °C

R Family

Medium Family

Platinum doping

L Family

Gold doping

Q

rr typ

(nC)

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AN3358 Main applications of 600 V ultrafast diodes

2 Main applications of 600 V ultrafast diodes

This section discusses the trade-offs in a common application. Boost power factor corrector
(PFC) will be widely covered since it is a major application. A typical PFC circuit is shown in

Figure 3.

2.1 Power factor corrector applications

Figure 3. Boost power factor corrector circuit

V

mains

L

V

gate

D

boost

I

RM

2.1.1 Boost diode in PFC working in continuous mode

Hard switching conditions

PFC applications are mainly designed in continuous mode when the power is greater than
200 W.

In such an application, it is well known that the greatest losses due to the diode are the
switching losses in the transistor (P
of the boost diode flows into the MOSFET (Figure 3). Consequently, the best choice in most
cases is the “R” family.

Switching losses due to I
temperature T

and the mains voltage V

j

depend mainly on two parameters: the operating junction

RM

Figure 4 and Figure 5 show that the switching losses for STTH8R06 quickly increase when

T

increases and when V

j

decreases. These curves are drawn with a software tool

mains

realized by these authors.

) when it turns on. The reverse recovery current (IRM)

ontr

.

mains

V

out

If the PFC only works on 240 V mains, with a low operating junction temperature, switching
losses will be less critical and the best trade-off could be the intermediate trade-off:
STTHxx06.

However, most PFCs are designed to work in a wide mains voltage range (85 V-264 V) with
an operating junction temperature (in the worst case) close to 100 °C. The “R” family will be
the family usually recommended.

Doc ID 018581 Rev 1 5/18

Main applications of 600 V ultrafast diodes AN3358

Figure 4. Switching losses versus Tj at turn off of the diode

P diode + P due to the diode (W)

off ontr

14

12

10

STTH8R06D

8

6

4

2

0

0 25 50 75 100 125 150 175

Figure 5. Switching losses versus V

P diode + P due to the diode (W)

off ontr

12

10

8

6

4

2

0

0 50 100 150 200 250 300

V = 90 V

mains

dI/dt = 400 A/µs

L = 0.5 mH

F = 100 kHz

sw

V = 400 V

OUT

P = 400 W

OUT

at turn off of the diode

mains

STTH8R06D

T = 100 °C

dI/dt = 400 A/µs

L = 0.5 mH

F = 100 kHz

sw

V = 400 V

OUT

P = 400 W

OUT

T (°C)

j

j

V (V)

mains

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