Q1 and Q2 is a darlington pair so you can get away with quite low Hfe. I usually use 50Hfe for Q1 and 60 Hfe for Q2. Keep in mind that the leakage needs to be as low as possible so russian ge trannies are great for Q1 and Q2.
At Q3 is where the "magic" happens. It needs some leakage, I ususally shoot for something close to 0,300 uA, Hfe 80-120.
What HFE am I looking for when building this ?
ReplyDeleteQ1 and Q2 is a darlington pair so you can get away with quite low Hfe. I usually use 50Hfe for Q1 and 60 Hfe for Q2. Keep in mind that the leakage needs to be as low as possible so russian ge trannies are great for Q1 and Q2.
DeleteAt Q3 is where the "magic" happens. It needs some leakage, I ususally shoot for something close to 0,300 uA, Hfe 80-120.