Patent GB-1250243-A (GB)
IPC: H03F1/30
Filed: 1969-05-14
Abstract: 1,250,243. Automatic voltage regulation; automatic control systems. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. May 14, 1969 [May 17, 1968], No. 24530/69. Headings G3R and G3X. An electrical circuit for generating a temperature-dependent output voltage and having an overall temperature co-efficient of resistance based on a resistive network and a transistor, comprises a resistive voltage divider forming at least part of the network and being in parallel with the emitter-collector path of the transistor whose base is connected to the divider tapping, and a circuit path incorporated in the network which path is of substantially zero temperature co-efficient and includes at least one Zener diode connected for reverse conduction, the output voltage being derived from the emitter-collector path of the transistor as a function of the collector current, and the circuit operation being such that the tapping connection determines the temperature co-efficient substantially independently of the circuit supply voltage. The embodiment shown in Fig. 3 is derived from a known circuit, Fig. 1 (not shown) in which the part of the voltage divider connected between the emitter and base of the transistor has a value smaller than that of the baseemitter input impedance of the transistor, and the current through the whole of the divider is less than the collector current of the transistor. The circuit of Fig. 3 retains the aforementioned features and is independent of the supply voltage Vs by virtue of the components 7, 8, 9, 9<SP>1</SP> added to the known circuit comprising members 1, 2, 3. Zener diode 7 has a temperature co-efficient which is substantially zero and a Zener voltage which is at least equal to the desired range of variation of the voltage Vs. If one Zener diode cannot provide both these requirements, a combination of one or several Zener diodes in series with one or several diodes connected in the forward direction may be used. By suitable choice of the values of resistor 8 and divider 9, 9<SP>1</SP>, it is shown by a theoretical analysis of the circuit that the temperature coefficient is dependent on the ratio of resistors 2, 3 and on the temperature co-efficient of the internal base-emitter resistance of the transistor 1. Resistor 8 may be omitted and the parallel circuit 7, 9, 91 connected between divider members 2, 3, the transistor base being connected to the tapping of divider 9, 9<SP>1</SP>, Fig. 4 (not shown). In this modification the working point of the transistor 1 is determined by the divider 9, 9<SP>1</SP>, but if it is not necessary for the collector current of transistor 1 to be variable the divider 9, 9<SP>1</SP> may be omitted and members 2, 3 may be in series with the Zener diode(s) and diode(s) with their tapping once again connected to the base of the transistor, Fig. 5 (not shown). The emitter-collector voltage of transistor 1 or the voltage across the resistor 6 may be used as a temperature dependent control signal for a control system for a temperature dependent element supplied by the voltage Vs, so that the controlled parameter of the element is maintained constant irrespective of temperature variations. Application of the invention to the circuits and control systems of Specification 1, 093, 316 is envisaged.