I don't think that the cascode CCS discussed in the tubes forum or Walt Jung's CCS can withstand my needs. 🙁
I need a current source that can delivers currents up to 100mA-200mA or more!
I need a current source that can delivers currents up to 100mA-200mA or more!
Forgot to add one more meter to measure the dc current that flows through the choke. Just to know how much is applied to it.
Now I'm reading Jung's article to understand better the cascode CCS circuit..... 😀
Now I'm reading Jung's article to understand better the cascode CCS circuit..... 😀
No, that won't work.
Put the choke vertically in the middle and put the HT supply and CCS in series, then their combination across the choke. That allows you to pass a constant current through the choke. Then add the AC source (the transformer) in series with the capacitor, and connect their combination across the choke. The DC can't go into the AC supply because the capacitor blocks it, and the AC can't go into the HT supply because the CCS blocks it. Both are forced to pass their currents through the choke.
The CCS would be better if it had an LED as the voltage reference from the base down to 0V, rather than just a resistor.
Put the choke vertically in the middle and put the HT supply and CCS in series, then their combination across the choke. That allows you to pass a constant current through the choke. Then add the AC source (the transformer) in series with the capacitor, and connect their combination across the choke. The DC can't go into the AC supply because the capacitor blocks it, and the AC can't go into the HT supply because the CCS blocks it. Both are forced to pass their currents through the choke.
The CCS would be better if it had an LED as the voltage reference from the base down to 0V, rather than just a resistor.
You are nearly there. I would post a diagram, but scanning is a bit tricky at the moment. You need an inverted CCS. That's to say, you need to turn the CCS upside down and replace NPN transistors with PNP transistors. The output terminal can then feed the choke as its path to 0V. Your AC department is fine.
Very nearly. The output of the CCS is the collector of the lower transistor, so this needs to go to the top of the choke. The upper line of the CCS (where the LED joins the resistor) need to go to the positive terminal of the power supply. The lower end of the resistor/LED string goes to power supply 0V and the bottom of the choke.
thanks!
Also thanks for the suggested transistors! How much current can this ccs apply to the choke?
Theoretically, it should be OK for 200mA. The limit is actually determined more by the dissipation in the MJE350 than current limits for the transistors. Suppose you decide to test with 50V AC. You would need to apply at least 100V of HT to the CCS to ensure that it didn't drop out. But if you were passing 200mA, that would mean the MJE250 would need to dissipate 20W (which is its maximum on an ideal heatsink). Moral: Heatsink the MJE350 carefully, and be wary about increasing current beyond 100mA and HT to the CCS beyond 50V.
Not a lot of free time the last few days 
I have some questions 😀
Is it possible to use 2 or 3 MJE250 (in parallel) to have more current?
I'll be very happy if my jig can deliver around 400-500mA.
What do you say?
I have some questions 😀
Is it possible to use 2 or 3 MJE250 (in parallel) to have more current?
I'll be very happy if my jig can deliver around 400-500mA.
What do you say?
Only with a complete redesign and making it considerably more complex. Try the simple circuit first and see how you get on, then think about making it more complex.
ok, let's start it and then will see!
I'll see what I have from junk, first.
For the AC I'll use a Variac. For the DC if I remember well I have an old transformer and maybe it's suitable for this purpose. I'll check tomorrow..........
I'll see what I have from junk, first.
For the AC I'll use a Variac. For the DC if I remember well I have an old transformer and maybe it's suitable for this purpose. I'll check tomorrow..........
Hi EC8010,
I am going to agree completely with you on the current vs inductance matter for iron cores. My LCR meter will only generate a 1 Vac signal with very low DC current capacity. I would need to build the jig if I wanted to do this.
Hi resident,
You really have to watch the dissipation as things will get hotter than you expect rather quickly. Don't skimp on the heatsink area. You might want to use a TO-3P package.
-Chris
I'm here to save you from that fate!
I am going to agree completely with you on the current vs inductance matter for iron cores. My LCR meter will only generate a 1 Vac signal with very low DC current capacity. I would need to build the jig if I wanted to do this.
Hi resident,
You really have to watch the dissipation as things will get hotter than you expect rather quickly. Don't skimp on the heatsink area. You might want to use a TO-3P package.
-Chris
- Status
- Not open for further replies.