Limit Vcc of IC
Limit Vcc of IC
(OP)
Hi everyone;
I want to keep the supply to an IC within 8-20 volts interval while the possible DC supply occurs within 10-30 volts from a battery. I used a 2.4 volts zener diode in series with the Vcc pin of IC to achieve the lower limit 8V theoretically but unable to limit the supply to IC to 20 volts when the DC input exceeds over that value.
Any considerations without using a regulator is needed.
Thanks.
I want to keep the supply to an IC within 8-20 volts interval while the possible DC supply occurs within 10-30 volts from a battery. I used a 2.4 volts zener diode in series with the Vcc pin of IC to achieve the lower limit 8V theoretically but unable to limit the supply to IC to 20 volts when the DC input exceeds over that value.
Any considerations without using a regulator is needed.
Thanks.





RE: Limit Vcc of IC
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RE: Limit Vcc of IC
RE: Limit Vcc of IC
Too bad - a 'low dropout' regulator set to something just over 8 volts would seem to be the otherwise-ideal solution (assuming that it meets your other, unstated, requirements).
I believe that some of these LDO regulators offer very low loss - the only significant power loss is due to the voltage drop across it (input to output). For a linear regulator, that is unavoidable in any case.
RE: Limit Vcc of IC
1)use a 20V zener diode (Vcc to Gnd) in series with a current limiting resistor from the variable supply input. This is still a "regulator" - but a shunt regulator - it may be more acceptable than a three-terminal device but will still dissipate the excess voltage as heat in the zener and limiting resistor when the supply goes over 20V.
2) design a special custom switching regulator which only starts to PWM-switch for voltages above 20V. Rather than always giving a fixed output voltage like a conventional switcher this design needs to be turned fully on below 20V so that it tracks the 10-20V area, then clamps at 20V and progressively chops the input supply at voltages above 20V to reduce power loss.
RE: Limit Vcc of IC
A series regulator is cheap and simple to design and build.
Assuming you have a positive voltage, why not use a LM317? You should be able to get a data sheet at Nationial Semiconductor. (? www.national.com) or Digi-key. (www.digikey.com)
RE: Limit Vcc of IC
RE: Limit Vcc of IC
'Okivrak' mentioned that the solution had to work with as little as a 2 volt differential (10v in, 8v out). The LM317 gets close to, or even over, that 2v limit in some circumstances (high current and/or low temperature).
Even if his I & T conditions fit (barely), the margin would be better with a LDO regulator. Also, with a LDO reg., he might be able to up the output to something better than 'just barely' 8.0 volts (margin again).
RE: Limit Vcc of IC
RE: Limit Vcc of IC
How much current do you need? How sensitive is your IC for
AC ? How many circuit do you need (one or mass production?)
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