ST UM0575 Manuale utente

February 2009 Rev 1 1/20

UM0575

User manual

STEVAL- IHT003V1, e-STARTER demonstration board

based on the ACST6 and X02

Introduction

The e-STARTER demonstration board (Figure 1) presents an innovative solution, patented

by STMicroelectronics, to reduce the power losses due to the positive thermal coefficient

(PTC) resistors in compressor starter circuits.

This solution features an ACST6 device which is used to turn off the PTC current after the

motor startup. It should be noted that the traditional PTC is still used in the electronic starter

circuit because it increases safety in case of ACST short-circuit or diode-mode failure (ref.

EN60335-1). This solution allows the starter standby losses to be decreased from typically

2.5 W to 380 mW or 40 mW, respectively for 230 V and 100 V applications.

The e-STARTER operation principle along with detailed schematics are given as well as

demonstration board performances and the method to adapt the circuit to a dedicated

compressor.

It should be noted that this board is not a "plug and play" solution. First, the PTC behavior

has to be checked (especially VPTC1 & VPTC2 levels as explained in Section 3.1) and then

the R4 resistor value has to be chosen before using the board with a compressor.

Figure 1. STEVAL- IHT003V1, e-STARTER demonstration board

AM01038v1

www.st.com

Contents UM0575

2/20

Contents

1 Operation principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1 Compressor starter application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 Standard PTC behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 e-STARTER operation mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3.1 Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3.2 ON state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Board performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1 Maximum current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Standby power losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 Fast transient voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.4 Surge voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5 Reliability and safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1 Voltage level setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.2 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Appendix A Component layout and printed circuit board . . . . . . . . . . . . . . . . . 15

Appendix B Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

UM0575 List of figures

3/20

List of figures

Figure 1. STEVAL- IHT003V1, e-STARTER demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Compressor starter application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 3. PTC operation, no RUN cap. (compressor OFF time > 10' mains: 198 V RMS) . . . . . . . . . 5

Figure 4. PTC operation with RUN cap.(compressor OFF time < 1' mains: 264 V RMS) . . . . . . . . . . 5

Figure 5. e-STARTER schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 6. Voltage spikes at zero current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 7. PTC turnoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 8. e-STARTER maximum current versus conduction time . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 9. Spurious e-STARTER triggering with a 2 kV surge (230 V compressor) . . . . . . . . . . . . . . 10

Figure 10. e-STARTER voltage limited to 648 V thanks to the RUN capacitor

(2 kV IEC61000-4-5 surge). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 11. VPTC1 and VPTC2 definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 12. e-STARTER connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 13. e-STARTER topside silk screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 14. e-STARTER SMD components layout (bottom view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 15. e-STARTER copper side (bottom view, dimensions in cm) . . . . . . . . . . . . . . . . . . . . . . . . 16

Operation principle UM0575

4/20

1 Operation principle

1.1 Compressor starter application

Single-phase induction motors, used for compressor control, use an auxiliary winding. This

winding permits a higher torque to be applied at startup. The most popular method to control

the start winding is to add a positive temperature coefficient (PTC) resistor in series with this

winding and the thermostat (Figure 2). Then, each time the thermostat is closed, the current

flows through the start winding and begins to heat the PTC. After a few hundreds of

milliseconds, the PTC value rapidly increases from a few W to several tens of kW. This

results in reducing the start winding current to a few tens of mA. This winding can then be

considered as open. The PTC then behaves like a switch in OFF state, but with a high

leakage current, resulting in high power losses (approx. 2.5 W).

Figure 2 gives the typical schematics of this application where a run or a start capacitor can

be connected in parallel (point 1) or in series (point 2) respectively with the PTC.

1.2 Standard PTC behavior

The transition between PTC ON and OFF states brings a voltage increase across this

variable resistor. Figure 3 and Figure 4 show two oscillograms of the same PTC in two

different operating conditions, for a 230 V compressor which can use both a start and run

capacitor. We see that, at the end of the PTC conduction, the voltage across it reaches

approximately 250 V (refer to "VPTC_OFF" indication). This voltage level is similar whatever

the operating conditions are (min or max RMS line voltage, run capacitor or not, etc.). The

PTC could be turned off as soon as this level has been reached. Section 1.3 explains how to

implement an electronic solution to achieve this function.

Figure 2. Compressor starter application

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UM0575 Operation principle

5/20

1.3 e-STARTER operation mode

1.3.1 Schematics

Figure 5 gives the typical schematics of an "e-STARTER" for a 230 V application. The

demonstration board presented here also features some optional pads to add a snubber

(components R6 and C4) as shown in Appendix A and B. The figure also gives the names of

the main electrical parameters which will be detailed in the following sections.

The traditional PTC resistor has to be connected between the "START" and the "PTC"

solder pads (refer also to Section 3.2).

Note: The C3 capacitor is not soldered on the breadboards. It can be added if one wants to

evaluate its impact on board immunity.

Figure 3. PTC operation, no RUN cap.

(compressor OFF time > 10' mains:

198 V RMS)

Figure 4. PTC operation with RUN

cap.(compressor OFF time < 1'

mains: 264 V RMS)

VPTC(100V/div)

IPTC(10A/div) VPTC_OFF

VPTC(100V/div)

IPTC(10A/div)

VPTC (100 V/div)

IPTC(10 A/div) VPTC_OFF

AM00899v1

PTC

(100V/div)

PTC_OFF

PTC

(10A/div)

AM00900v1

Operation principle UM0575

6/20

1.3.2 ON state

As soon as the mains voltage is applied:

●M1 is OFF because the voltage drop across the PTC is not high enough to reach the

DZ1 clamping level

●T2 is then turned on, thanks to the gate current provided by R2

●T1 is turned on thanks to the gate current provided by T2

Both T1 and the PTC are then ON.

At each zero-current crossing point, the ACST6 turns off. The reapplied voltage across

T1/T2 triggers back T1 which results in some voltage spikes at each zero-current crossing

point (typically around 40 V as shown in Figure 6 for a 230 V compressor).

Applying the click test of norm EN55014, the noise duration could last more than 200 ms

(depending on the type of compressor and PTC). The individual spikes last a few hundreds

of microseconds and are spaced at intervals of 10 ms, so the limits of continuous

disturbance are applicable. Since the spike peaks are less than 100 V, the e-STARTER

solution should fulfill the requirements of EN55014. It should be noted that tests results

greatly depend on the compressor used during the tests.

Figure 5. e-STARTER schematics

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UM0575 Operation principle

7/20

When the PTC conduction time has been sufficient to start the compressor, its voltage

suddenly rises. This voltage rise is sensed by the R3/R4 divisor bridge.

If the level is higher than the DZ1 clamping level, the thyristor, consisting of Q1 and Q2, is

latched. M1 is then turned on.

As M1 is ON, there is no more gate current to trigger T2, so T1 also stays OFF. The PTC is

then turned off.

No more current circulates through the PTC, thus no power is dissipated in it.

Figure 7 shows the typical behavior of this circuit. The C1 capacitor voltage gives an image

of the PTC voltage. When its value reaches the DZ1 clamping level (15 V), the MOS gate is

latched to 15 V. The PTC is then turned off (refer to the IA ACST6 current waveform).

Figure 6. Voltage spikes at zero current

Figure 7. PTC turnoff

(5A/div)

(20V/div)

(5 A/div)

(20 V/div)

AM00902v1

(5A/div)

(10V/div)

AM00903v1

Board performances UM0575

8/20

2 Board performances

2.1 Maximum current

During e-STARTER conduction, the power losses are similar to those of the standard PTC

solution as the same current circulates through this resistor. The only difference is that a

small part of the voltage is also held by T1.

In the case of an ACST6, its forward voltage drop can be considered to be a constant

forward voltage, Vt0, of at worst 0.8 V and a dynamic resistance, Rd, of at worst 80 m. So

even with a 10 A peak current, the voltage drop is less than 1 V.

This forward voltage drop should be taken into account mainly to evaluate the junction

temperature elevation of the semiconductor switch.

For an ACST6 in the TO220AB package, without any heatsink, this junction temperature

elevation is equal to:

●30° C after a 5 A RMS current during 3 s (worst case of typical 100 V/60 Hz

compressors)

●50° C after an 11 A RMS current during 0.5 s (worst case of typical 230 V/50 Hz

compressors)

This ensures that TJremains below its maximum allowed temperature (125° C), even with a

75° C initial temperature. Figure 8 gives the maximum repetitive RMS current that the

ACST6-7ST can withstand without any heatsink. This curve is given for 40° C and 75° C

ambient temperatures. As with the e-STARTER solution, the heating time of the PTC is not

long enough to warm the electronic devices, so the 40° C curve is closer to the real

e-STARTER operating conditions.

2.2 Standby power losses

During e-STARTER standby, the losses are caused only by the resistors, which are still

connected to the mains voltage. Indeed, the ACST leakage current is in practice very much

lower than 20 µA so that the resulting losses can be neglected.

Figure 8. e-STARTER maximum current versus conduction time

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UM0575 Board performances

9/20

The two resistors which are mainly dissipating power at standby are:

●R2 - used to provide T2 with gate current during the e-STARTER on state

●R3 - used to sense the voltage level across the PTC

As R2 is connected just behind the diodes’ bridges, the VAK voltage is applied across it, in

full-wave mode. R3 senses only half the voltage across the PTC and T1. This voltage is also

equal to VAK as T1 is OFF, and so no current is circulating through the PTC.

We can neglect the voltage drops of M1 and of C1, which are lower than 0.6 V and 16 V

respectively. The power losses, dissipated by the two resistors, are given by the following

equations:

Equation 1

An example with R2 = 470 kΩand R3 = 510 kΩgives:

●For a 230 V / 50 Hz application using a run capacitor, VAK can reach up to 350 V RMS.

The overall power losses then equal 380 mW.

●For a 100 V / 60 Hz application using or not a run capacitor, VAK stays around the line

voltage, i.e at worst 115 V RMS. The overall power losses then equal 41 mW.

2.3 Fast transient voltages

Immunity tests, as described by the IEC 61000-4-4 standard, have been performed with the

schematics of Figure 5, connected in series with a compressor without a RUN or START

capacitor. e-STARTER spurious triggerings have not been detected with spikes up to 2 kV.

This high immunity level has been reached thanks to:

●the high dV/dt capability of the ACST6

●the improved dV/dt capability of the very sensitive SCR X0202M (20 µA < Igt < 50 µA)

thanks to the fact that its gate is short-circuited to the cathode via M1 in OFF state, and

also thanks to the R6-C4 snubber circuit

●the RGK (R7) resistor which is added on the ACST6 device to derivate the current

provided by R2 when M1 is ON

●the immunity provided by the layout of the printed circuit board (refer to Figure 15)

It should be noted that spurious triggering of the e-STARTER is not a problem as such

behavior is not seen by the end user, and as these turn-ons do not lead to any component

failure.

2.4 Surge voltages

The ACST6 device is an overvoltage protected device which means that it can be used

without any varistor in parallel with its terminals. If a high energy surge is applied to the

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Board performances UM0575

10/20

mains, as described in the IEC 61000-4-5 standard, when the e-STARTER is off, two cases

can occur:

●A no-run capacitor is connected across the e-STARTER: the surge voltage is then

entirely held by the ACST6. If the energy is high enough, the leakage current of the

device can exceed its break-over level, leading to a turn-on of the e-STARTER lasting

at worst 10 ms (refer to Figure 9).

●A run capacitor is used: the surge energy is absorbed by this capacitor. The voltage

level is then limited below 1 kV, which is the typical clamping level of the ACST6. No

spurious turn-on occurs in this case (refer to Figure 10).

It should be noted that in case of a spurious triggering in break-over mode, the ACST6

current is limited by the START winding inductance. The current value is then typically in the

range of 2 A. This is far below the level guaranteed with ACST6, where a 47 Ωload can be

used in such operation mode (refer to the ACST6 datasheet). With a 2 kV surge, the peak

current then equals 40 A in this case.

2.5 Reliability and safety

Reliability tests have been performed with ACST6-7ST samples submitted to a current

shape equivalent to an inrush current of 11 A RMS during 0.5 s. No parameter evolution of

these samples has been detected after 450,000 cycles, which is representative of the

lifetime of a refrigerator. This result demonstrates the excellent capability of these 6 A

products even for applications with high inrush currents.

Concerning safety, the EN6033561 standard imposes the consideration of short-circuit or

diode-mode failures of all silicon power switches involved in safety features. The failure of an

entire e-STARTER cannot lead to safety issues (electrical or mechanical shock, fire). If the

e-STARTER power switch dies in short-circuit or diode-mode, the start winding current is still

limited by the PTC. The start winding is then protected and the compressor still works.

Indeed, the starter function is still ensured by the PTC. The only drawback is that the

standby losses increase back to 2.5 W.

Figure 9. Spurious e-STARTER triggering

with a 2 kV surge (230 V

compressor)

Figure 10. e-STARTER voltage limited to 648 V

thanks to the RUN capacitor (2 kV

IEC61000-4-5 surge)

VAK

AM00905v1

+ 648V

VAK

VMAINS

+ 648V

VAK

VMAINS

AM00906v1

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