At 14.55 2012.05.22, you wrote: >On Tue, May 22, 2012 at 2:43 AM, Electron wrote: >> >> Hi, >> I have a IC which, in the datasheet, is said to need a powerup rise time= not >> slower than 100uS in order to initialize correctly. Effectively it=20 >doesn't work >> if the power ramps up slow, and there's no reset input, power must=20 >be disconnected >> in order to attempt a new successfull turn on. >> >> How would you ensure fast powerup rise time? The power turns on /=20 >ramps up very >> slowly, and I can't help it. >> > >I'd use a circuit like this: >http://i.imgur.com/Hr8Aa.png > >Replace R2 with the load. >D1 zener voltage is at least 700mV below the required turn-on voltage. >Add feedback resistor from load supply to base of Q1 to make it latch on. Yup, this is the PMOS solution.. I don't need the zener part as I have a error signal I can use instead. Just wanted to ask you, why R3 is just 2.2K? Wouldn't a higher value work as well, and waste less power in the resistor? Cheers, Mario >--=20 >Martin K. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .