GB1245233A - Electrical analogue circuits simulating the transient thermal resistance of a semiconductor device - Google Patents

Abstract

1,245,233. Electric analogue simulating circuits. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 18 Oct., 1968 [19 Oct., 1967], No. 47681/67. Heading G4G. [Also in Division H2] An analogue circuit simulates the D.C. transient thermal resistance of a semi-conductor device (e.g. a thyristor or junction rectifier), i.e. the ratio of temperature rise for t seconds of constant power input to the power input (Fig. 1), for a step change of power dissipation. In Fig. 2, plural series resistances R 1 to R n are shunted by capacitances C 1 to C n and receive a step direct current input I to cause a rise or fall of unidirectional voltage V across the circuit given by where t is elapsed time from step input. I is proportional to internal power dissipation of the device, or to the product of load current and voltage drop. V is proportional to internal temperature rise of the device and the transfer function of the circuit is proportional to the D.C. transient thermal resistance. The branch time constants are determinable by a computer programme fitting the sum of the exponential to experimental data of the transient thermal n resistance for α r to be +ve, and # A r is pror=1 portional to the steady state thermal resistance. In a modification (Fig. 3, not shown) incorporating the dual of the circuit of Fig. 2, a step unidirectional voltage V<SP>1</SP> is applied across plural parallel branches each comprising a resistance R<SP>1</SP>r<SP>1</SP> and inductance L<SP>1</SP>r, in series to produce a unidirectional current I<SP>1</SP> given by wherein t<SP>1</SP> = time elapsed since step, is proportional to the steady state thermal resistance, voltage V<SP>1</SP> is analogous to power dissipation, current I<SP>1</SP> is analogous to temperature rise. The circuits are applicable to over-current protection of the devices. Specification 1,081,585 is referred to.