Fast Turn-off Thyristor P0248SC12x
The total dissipation is now given by:
W(TOT) W(original) E f
12.2 Determination without Measurement
In circumstances where it is not possible to measure voltage and current conditions, or for design
purposes, the additional losses E in joules may be estimated as follows.
Let E be the value of energy per reverse cycle in joules (curves in Figure 9).
Let f be the operating frequency in Hz
TSINKnew TSINKoriginal E Rth f
Where TSINK (new) is the required maximum heat sink temperature and
TSINK (original) is the heat sink temperature given with the frequency ratings.
A suitable R-C snubber network is connected across the thyristor to restrict the transient reverse voltage
to a peak value (Vrm) of 67% of the maximum grade. If a different grade is being used or Vrm is other than
67% of Grade, the reverse loss may be approximated by a pro rata adjustment of the maximum value
obtained from the curves.
12.3 Reverse Recovery Loss by Measurement
This thyristor has a low reverse recovered charge and peak reverse recovery current. When measuring
the charge care must be taken to ensure that:
(a) a.c. coupled devices such as current transformers are not affected by prior passage of high
amplitude forward current.
(b) A suitable, polarised, clipping circuit must be connected to the input of the measuring oscilloscope
to avoid overloading the internal amplifiers by the relatively high amplitude forward current signal
(c) Measurement of reverse recovery waveform should be carried out with an appropriate critically
damped snubber, connected across diode anode to cathode. The formula used for the calculation
of this snubber is shown below:
R2 4 Vr
Where: Vr = Commutating source voltage
CS = Snubber capacitance
R = Snubber resistance
13.0 Gate Drive
The recommended pulse gate drive is 30V, 15 with a short-circuit current rise time of not more than
0.5µs. This gate drive must be applied when using the full di/dt capability of the device.
The duration of pulse may need to be configured with respect to the application but should be no shorter
than 20µs, otherwise an increase in pulse current could be needed to supply the resulting increase in
charge to trigger.
Data Sheet. Type P0248SC12x Issue 2
Page 5 of 12