I thought it would be easy...! I have some electronics (a project) that needs a regulated voltage, from a 3.3 V regulator (KA278R33). Connected to ca 12 V.
I also want to switch this electronics on and off with a toggling flip/flop. Therefore, the flip/flop always needs voltage. In order to make the circuit use very low current when off I thought of using the 74ac74 or the hc74. But, those boys mustn´t be given more than 5.5/6 volts so then, i thought of a simple resistor and a zener diode of around 6-7 volts because if the resistor is a high one, say like 50000 Ohms, then the zener voltage will drop to around 5 Volts which matches the flip/flop. (Zeners need around 5 (oh a little spider on my keyboard).. mA. ) The zener<->resistor is connected to the unregulated voltage, which is always on. And of course, on the flip/flop the Q inv. output is connected to the D input etc and Q to an npn(-darlington) transistor in front of the KA278R33.
The regulator is a low drop type and needs >3.8 Volts. The darlington´s
double Vbe voltage is ca 2x0.2=1.2. So the input darlibgton base voltage
has to be 5 Volts or more.
Well... does anyone know of a certain voltage regulator or circuit that has all of this in a chip? I have searched extensively with no results. I think it´s strange. I got hold of LDO-regulators from Fairchild, (KA)278R05 that has an enable input. However, in off-mode it draws 2.5 mA as measured.
Does anyone know of a regulator with a much less current need while being in the disenable mode. It shall handle ca 1A.
A regulator that would switch on/off by a clock pulse and have a very very low off current and also a low quiscent current, say 10 mA would be acceptable.
I guess there is no circuit like that.
Anyway, any comments are welcome. Any other ways to do it?
Regards,
Dick - Sweden
I also want to switch this electronics on and off with a toggling flip/flop. Therefore, the flip/flop always needs voltage. In order to make the circuit use very low current when off I thought of using the 74ac74 or the hc74. But, those boys mustn´t be given more than 5.5/6 volts so then, i thought of a simple resistor and a zener diode of around 6-7 volts because if the resistor is a high one, say like 50000 Ohms, then the zener voltage will drop to around 5 Volts which matches the flip/flop. (Zeners need around 5 (oh a little spider on my keyboard).. mA. ) The zener<->resistor is connected to the unregulated voltage, which is always on. And of course, on the flip/flop the Q inv. output is connected to the D input etc and Q to an npn(-darlington) transistor in front of the KA278R33.
The regulator is a low drop type and needs >3.8 Volts. The darlington´s
double Vbe voltage is ca 2x0.2=1.2. So the input darlibgton base voltage
has to be 5 Volts or more.
Well... does anyone know of a certain voltage regulator or circuit that has all of this in a chip? I have searched extensively with no results. I think it´s strange. I got hold of LDO-regulators from Fairchild, (KA)278R05 that has an enable input. However, in off-mode it draws 2.5 mA as measured.
Does anyone know of a regulator with a much less current need while being in the disenable mode. It shall handle ca 1A.
A regulator that would switch on/off by a clock pulse and have a very very low off current and also a low quiscent current, say 10 mA would be acceptable.
I guess there is no circuit like that.
Anyway, any comments are welcome. Any other ways to do it?
Regards,
Dick - Sweden