I'm trying to combine several SMPSs each having a ~350VDC output @100mA each.
Purchased an unused batch of small DC->DC SMPSs in good industrial quality. Unfortunately they're too weak for my purpose.
- Input 24-30VDC
- Output adjustable 75VDC-400VDC @ 40W max load.
- Non-isolated ( Input and Output shares GND. )
- Switching circuit operating ~ 75KHz.
- Measured: 350V @ 100mA => Ripple < 3V.
The SMPSs have built-in soft-start + short-circuit protection, but apart from adjustable voltage, they have no other control-options.
I was hoping to combine say 7 of these SMPSs using "simple" non-foldback current-limiters and connect their outputs in parallel. (The current-limiter in mind is almost similar to the ones described in this topic.)
In my case one dedicated SMPS is used to drive the voltage (emitter follower.)
The "driver" will deliver the desired voltage and the remaining SMPSs should be in current limiting mode, sharing the load equally between them.
At least, that's the result I'm aiming for. ;-)
There should be a total of 7 or 8 current sources. ( Only 3 is shown here ).
Resistors / Capacitors / Voltages has not been calculated.
- Is the constant voltage driver + several current limiters a good approach?
- Do I need diodes ( D2 - D8 ) at the output of each current limiter?
- Is it necessary to have a resistor ( R1 ) or a "current limiter" in series with the output of the CV-mode "driver" ?
Having a "driver" capable of delivering relatively high current should eliminate the need for Darlington BJTs as serial regulators.
However this also means that the current-limiting "bypass" BJTs need to deal with higher currents.
- Can I use normal BJTs ( TIP50G or MJE18004G ) or are Darlington BJTs a requirement?
Can I use 2 standard BJTs in a Darlington setup?