J Jony130 Active Member Feb 24, 2013 #1 Hi. Can you hale my prevent this constant current source circuit from oscillation. Why this circuit even start to oscillate? Maybe the circuit is bad? Attachments 1.PNG 19 KB · Views: 193 Draft77.asc 2.2 KB · Views: 116 Last edited: Feb 24, 2013
Hi. Can you hale my prevent this constant current source circuit from oscillation. Why this circuit even start to oscillate? Maybe the circuit is bad?
ronsimpson Well-Known Member Most Helpful Member Feb 24, 2013 #2 Add a 100pf cap from output to (-) of U1. Break connection from U2 out to U1 in(-). Now add 10k resistor to get the connection back. The new RC slows down the error amp U1. It ts too fast and too much gain.
Add a 100pf cap from output to (-) of U1. Break connection from U2 out to U1 in(-). Now add 10k resistor to get the connection back. The new RC slows down the error amp U1. It ts too fast and too much gain.
J Jony130 Active Member Feb 24, 2013 #4 ronsimpson said: Add a 100pf cap from output to (-) of U1. Break connection from U2 out to U1 in(-). Now add 10k resistor to get the connection back. The new RC slows down the error amp U1. It ts too fast and too much gain. Click to expand... THX I try this tomorrow Roff said: Here is a much simpler circuit: View attachment 71281 Click to expand... But I need a circuit with low Rr voltage drop (Vcc = 5V) and with high Vin voltage to set the current (from 0 to 4V).
ronsimpson said: Add a 100pf cap from output to (-) of U1. Break connection from U2 out to U1 in(-). Now add 10k resistor to get the connection back. The new RC slows down the error amp U1. It ts too fast and too much gain. Click to expand... THX I try this tomorrow Roff said: Here is a much simpler circuit: View attachment 71281 Click to expand... But I need a circuit with low Rr voltage drop (Vcc = 5V) and with high Vin voltage to set the current (from 0 to 4V).
Roff Well-Known Member Feb 24, 2013 #5 Jony130 said: THX I try this tomorrow But I need a circuit with low Rr voltage drop (Vcc = 5V) and with high Vin voltage to set the current (from 0 to 4V). Click to expand... If you use an op amp with rail-to-rail I/O, it should work. If your collector resistor is really 100Ω, and your maximum current is 4V/10Ω=400mA, then you will need a collector supply voltage much higher than 12V.
Jony130 said: THX I try this tomorrow But I need a circuit with low Rr voltage drop (Vcc = 5V) and with high Vin voltage to set the current (from 0 to 4V). Click to expand... If you use an op amp with rail-to-rail I/O, it should work. If your collector resistor is really 100Ω, and your maximum current is 4V/10Ω=400mA, then you will need a collector supply voltage much higher than 12V.