Thyristor/TRIAC

Which method to control AC (50 Hz/60 Hz) by controlling phases is preferable, the method of using two thyristors connected in reverse series, or the method using only one TRIAC?

The method using one TRIAC is recommended.
TRIACs were developed for controlling AC circuits.
An AC circuit using a TRIAC can be simplified in configuration and its cost can be lowered, as compared with a circuit using thyristors.

I am using the triac AC08DGM, but its operation is unstable at small loads. Why is this so?

The minimum current of the triac is defined as holding current that is the minimum on-state current at which the ON state can be maintained. Holding current of a product with large rated RMS on-state current is large. If a product with a large rated RMS on-state current is used with a small load, the on-state current falls below the holding current, causing malfunctioning.
Use a product with a small holding current.

(2008/02)

A thyristor may switch on even without a gate trigger signal.
What are the possible causes?

Have you taken any action against false firing due to dV_D/dt?
If not, insert the following resistance and capacitance, as shown in the figure below, to prevent false firing.
Decide the values of C and R, taking the operating temperature range and noise environment into consideration.

(2008/04)

A cause of malfunctioning of a thyristor is critical rate rise of off-state voltage dV_D/dt. What is this critical rate rise of off-state voltage dV_D/dt?

dV_D/dt is an inclination of rising of the applied voltage as shown below when a surge voltage is superimposed onto the AC supply voltage waveform or when the switch is turned ON.
If this abruptly rising voltage is applied to the anode as a positive voltage and to the cathode as a negative voltage, the thyristor faultily turns ON.
For the thyristor, the maximum voltage rise rate at which the product does not change its state from the OFF state to the ON state is defined as critical rate rise of off-state voltage dV_D/dt [V/us].

(2008/02)

What are the temperature characteristics of dV_D/dt?

The higher the temperature, the lower the dV_D/dt.
This is because gate trigger current IGT has a positive temperature coefficient and the sensitivity seems to increase at a high temperature (which means that the thyristor is likely to turn ON by malfunction).

(2008/02)

I heard that production of the AC08FSM has been stopped.
I believe that the AC08FSMA is the substitute. How do these products differ?

The dielectric strength voltage decreases because of the difference in package.
The AC08FSMA has the cut of the pin of a lead frame exposed.
Consequently, a dielectric strength voltage of 1500 V is not guaranteed.

(2007/09)

Why has the AC08FSM been discontinued and replaced by the AC08FSMA?

This is a part of a package standardization effort.
The AC08FSMA package MP-45 is being adopted as a standard package.

(2007/09)

What is a holding current?

It is the minimum anode current that can hold the ON state of a thyristor or TRIAC when it is switched on by a gate trigger current.
The thyristor or TRIAC that has been once switched on is kept in the ON state if the holding current flows even if the gate current is stopped.
To switch it off, the anode current must fall below the holding current, or the anode must be kept negative (biased in the reverse direction) for some time.

Why "5 mA (MAX.)" is rated for the holding current in "Electrical Specifications"?
I guess the minimum current value should be rated.

The holding current of 5 mA (MAX) is the rated value of NEC Electronics and means that the product has a characteristic of the 5 mA or less holding current.
When the product is viewed from the user, the ON state can be accurately held if a holding current of 5 mA or more, higher than the value shown in the catalog, is flown.

It is shown in the Data Sheet of the 03P2J that V_DM = 24 V and I_TM = 1 A as the conditions of the holding current. What are the voltage and current values of V_DM and I_TM?

V_DM = 24 V and I_TM = 1 A are the voltage and current between the anode and cathode.
It is confirmed that the ON status is held at 5 mA or greater by gradually decreasing the holding current from these conditions.

(2008/04)

Are the TRIACs used correctly in the forwarding/reversing circuit of the motor in the basic circuit example below?

If one of the TRIACs is ON and the other TRIAC which has been off switches on in the forwarding/reversing circuit of a motor, a charging loop that charges phase advancing capacitor C1 is created.
As a result, an extremely large pulse current flows through the two TRIACs, damaging them.

To prevent this, limit the discharging current from phase advancing capacitor C1.
It is recommended to insert inductance L in series with C1 as shown in the circuit example below.

How exactly is the absolute maximum rated fusing current calculated?

The fusing current is calculated by multiplying the squared pulse current value by the pulse width.

(2006/12)

When the ambient temperature was 45°C, the surface temperature measured at the metal fins of the AC10DGM was approximately 55°C, but is this temperature a problem considering triac performance and functions?

Verification of the junction temperature (Tj) is required to determine whether or not this temperature is a problem.
In the case of the AC10DGM, the thermal resistance Rth(j-c) between the junction and the case is 1.8°C/W, so that at the ambient temperature of 45°C, the following Tj value is obtained when the measured temperature (Tc) is approximately 55°C:
Tj = 1.8 × Pd + 55
Please calculate Pd and check whether Tj is equal to or lower than the junction temperature of 125°C in the above equation.

[Related FAQ]
Thermal design

(2006/12)

How are the thyristors and triacs marked?

They are marked as shown below.

(1)TO-92 package



SCR

Marking	Product name
P2M	03P2M
P4M	03P4M
P4G	03P4MG
P6G	03P6MG

TRIAC

Marking	Product name
0V8D	AC0V8DGM
01D	AC01DGM

(2)SOT-89 (power mini-mold) package



SCR

Marking	Product name
JB	03P2J
JD	03P4J
JE	03P5J

TRIAC

Marking	Product name
1D	AC01DJM

(3)MP-3,MP-3Z



SCR

Marking	Product name
3P4J	3P4J,-Z
5P4J	5P4J,-Z
5P6J	5P6J,-Z
8P4J	8P4J,-Z

TRIAC

Marking	Product name
AC03D	AC03DJM,-Z
AC03F	AC03FJM,-Z
AC05D	AC05DJM,-Z
AC05F	AC05FJM,-Z

(4)TO-202AA(MP-7)



SCR

Marking	Product name
2P4M	2P4M
2P6M	2P6M
2S2M	2S2M
2S4M	2S4M
2V5P4	2V5P4M
3P4MH	3P4MH
3P6MH	3P6MH

TRIAC

Marking	Product name
AC03D	AC03DGM
AC03F	AC03FGM

(5)TO-220AB(MP-25)



SCR

Marking	Product name
5P4M	5P4M
5P6M	5P6M
8P2M	8P2M
8P4M	8P4M

TRIAC

Marking	Product name
AC05D	AC05DGM
AC05F	AC05FGM
AC08D	AC08DGM
AC08F	AC08FGM
AC10D	AC10DGM
AC10F	AC10FGM
AC12D	AC12DGM
AC12F	AC12FGM
AC16D	AC16DGM
AC16F	AC16FGM

(6)Isolated TO-220(MP-45) package



SCR

Marking	Product name
5P4	5P4SM
5P6	5P6SM
5P4A	5P4SMA
5P6A	5P6SMA
8P2	8P2SM
8P4	8P4SM
8P2A	8P2SMA
8P4A	8P4SMA

TRIAC

Marking	Product name
03D	AC03DSM
03F	AC03FSM
03DA	AC03DSMA
03FA	AC03FSMA
05D	AC05DSM
05F	AC05FSM
08D	AC08DSM
08F	AC08FSM
10D	AC10DSM
10F	AC10FSM
12D	AC12DSM
12F	AC12FSM
16D	AC16DSM
16DA	AC16DSMA

(2006/10)

Are there substitutes for the 350P12S (SCR)?

Sorry, there are no substitutes.
The specifications of the 350P12S are 350 A, 1200 V.
Currently we do not offer SCRs for such a large current and high voltage.

(2007/03)

What rating is the effective on-state current?

It is defined as an effective value (Root Mean Square) of the current that is allowed to continuously flow through a thyristor or triac under a specific condition.
The effective on-state current is limited by the condition that the current density at the junction, current capacity of constituent components, temperature rise and so on do not exceed the permissible values. Therefore, since the effective on-state current rating is determined by element design and does not change even if the cooling condition is changed, the product must not be used with a current exceeding this value regardless of the ambient temperature, the case temperature, or the waveform of the current.

(2007/08)

What rating is the average on-state current?

It is the average value of a current that is allowed to flow through a thyristor in the forward direction under specified temperature, current waveform and frequency conditions and is the average value in one cycle. Generally, it is the value when a single-phase half wave of 180° is allowed to flow at a commercial frequency of 50/60 Hz. Therefore, the triac does not have this rating.

(2007/08)

What is the frequency range in which the average on-state current rating can be applied?

The frequency is usually limited to a range of 50 to 400 Hz. This is because, if the frequency is too low, the junction temperature could rise beyond the permissible value while the on-state current flows. The reason for the upper limit of the frequency is that, as the frequency increases, the temperature inside the thyristor unevenly rises, exceeding the rating at some parts even if the average temperature is within the permissible range.

(2007/08)

The Data Sheet of the 8P4SMA defines as gate trigger characteristics that gate trigger current I_GT is 10 mA max. and gate trigger voltage V_GT is 1.5 V max. Figure 4 also shows an example of gate characteristics.
Is it all right to consider that these characteristics and figure show that the thyristor turns on at 25°C if the gate trigger current and voltage are within the shaded range in the figure?

No, it is not.
The characteristic specification and the characteristic example in Figure 4 mean that the gate trigger current and voltage of all the 8P4SMAs shipped from our factories are less than 10 mA and 1.5 V, and that the design is needed to make the higher current flow to the thyristor when it is actually used.
The shaded part on the figure indicates that the characteristics of all these products are distributed within this range.
This means that the gate trigger condition at Tj = 25°C is 10 mA and 1.5 V and that a current higher than those in the shaded range must flow.
Note that a PN-junction diode is configured between the gate and cathode of the thyristor. So, the characteristics between the gate and cathode include components of parallel resistance and series resistance that adjust the gate sensitivity.
To turn on the thyristor, both the gate trigger current and voltage must be taken into consideration. However, the voltage is considered as a result generated by flowing a current between the pins.
To turn on the thyristor, therefore, a current higher than the maximum value of the gate trigger current must be suddenly flowed.
If the supply voltage to cause the current to flow is lower than the rated gate trigger voltage at this time, the gate trigger current cannot accurately flow.

(2008/04)