VVV
Advanced Member level 5
Re: Regulators help pls
The LM385 is actually an integrated circuit that works like a Zener, but it has a low voltage and it's thermally compensated. That is done using a Widlar voltage reference. Using diodes will work, but the regulation will be poor, because the voltage drop varies significantly with the current. Thermal stability will also be poor because the voltage drop depends on temperature.
Anyway, I said I would post the schematic, so here it is, for whatever it's worth. Transistors Q3, Q4, Q5 form a 1.2V Widlar voltage reference, while Q1, Q2 work as a differential amplifier. The circuit should draw about 300µA. However, the input voltage range is limited: 7 to 12V. If you need another range R8 should change.
Transistors Q1-Q5 are part of the CA3045/6 (caution, 15V max) or CA3146 or CA3086. Using a transistor array will give you the best regulation and thermal stability..
Capacitor C1 may be needed to prevent, start with 47pF and increase it if necessary.
My best advice: look for a real low Iq linear regulator, it's the best choice. Discrete circuits get very complicated as you require higher performance. For example, this circuit could benefit from a current source instead of R8.
The LM385 is actually an integrated circuit that works like a Zener, but it has a low voltage and it's thermally compensated. That is done using a Widlar voltage reference. Using diodes will work, but the regulation will be poor, because the voltage drop varies significantly with the current. Thermal stability will also be poor because the voltage drop depends on temperature.
Anyway, I said I would post the schematic, so here it is, for whatever it's worth. Transistors Q3, Q4, Q5 form a 1.2V Widlar voltage reference, while Q1, Q2 work as a differential amplifier. The circuit should draw about 300µA. However, the input voltage range is limited: 7 to 12V. If you need another range R8 should change.
Transistors Q1-Q5 are part of the CA3045/6 (caution, 15V max) or CA3146 or CA3086. Using a transistor array will give you the best regulation and thermal stability..
Capacitor C1 may be needed to prevent, start with 47pF and increase it if necessary.
My best advice: look for a real low Iq linear regulator, it's the best choice. Discrete circuits get very complicated as you require higher performance. For example, this circuit could benefit from a current source instead of R8.