Current Source - Half Bridge Resonant Converter - Page 1
Forum section: electronics / projects

author: akhi
author_rank: Newbie
timestamp: August 21, 2023, 02:35:23 pm
content: Dear community,I want to improve the design of a resonant constant current source that is used to supply many PCBA through one wire. Each PCBA has a current transformer at its input followed by a full bridge diode rectifier. After rectification the voltage is fixed at a DC value by using a current limiter (simple zener-transistor regulator). All PCBA doesn't have same output voltage and their number can vary from application to an other. As well each PCB supply a different load (zero to full power).The topology of the converter is a half bridge resonant inverter. The resonant parts are basically a transformer (Tr), a Tank inductor (LT) and two capacitors (Cr). Because of the variety of loads (PCBA with different voltages, different power) the half bridge inverter is regulated by sensing the primary side RMS current of the transformer through AUX winding. A1 and A2 act as VCO to produce a constant pulse width to drive HS and LS IGBTs. The HS is drive at the rising edge of the regulation frequency while the LS is driven at the falling edge (Red: LS Vgs, Blue: HS Vgs, Green: Primary Current).The first improvement I want to achieve is regarding the efficiency of the converter. Since the resonance frequency depend on the number of loads it could not be predicted. So, the converter can not be regulated at the resonance frequency to improve the efficiency. So, any advice how can I improve efficiency? Is is better to use MOSFETS instead of IGBTs in such industrial application?The second improvement is a limitation in the number of the total loads (PCBAs). I have found a "rule" that claims that the secondary voltage reflected back to the primary side transformer (Tr) should not exceed VDC/4. I can see from the math that beyond this value the die diode of the IGBT will start conducting (LS or HS depend on the current direction). But what I do not understand is why this will be a problem? This "rule" is really limiting to increase number of loads, so the only solution is to increase the VDC voltage which is enough high.I believe that the same topology with primary side regulation is used in induction cooking or in LED String lighting, but I am not able to find any detailed application notes. Most of what I have found so far is for a constant power load. So, if you have any paper for such design I am thankful.Update1: Here is a similar application of what I want to achievehttps://vtechworks.lib.vt.edu/bitstream/handle/10919/101507/Yan_N_T_2020.pdf?sequence=1&isAllowed=y

author: jbb
author_rank: Super Contributor
timestamp: August 21, 2023, 10:43:07 pm
content: Oh snap! I tried something like that for a project once upon a time. I did a backplane and a row of daughter boards. Each daughter board had a toroid and a hole in the PCB so I could poke the 1 turn primary through the whole stack in one go.On converter operation:- operating exactly on resonance could cause excessive current flow into the clamping Zener diodes- you probably want to operate a bit above resonant frequency so that you’re comfortably operating in the inductive mode (which mis much gentler on the primary switches- are you using high permeability toroids, ie have a (relatively) high magnetising inductance?

author: jonpaul
author_rank: Super Contributor
timestamp: August 21, 2023, 11:02:32 pm
content: What choose 1/2 br resonant?Other topologies are simpler and may remove the issues ...Watts thruput?Bus V? I loa?Current or voltage source for load?j

author: akhi
author_rank: Newbie
timestamp: August 22, 2023, 11:53:56 am
content: Quote from: jbb on August 21, 2023, 10:43:07 pmNice to hear that you have tried same... do you have any schematics to share? I'll put a thesis that I found this morning that seems to treat about the subject, but apparently not regulated at primary side.I am not sure to operate a bit above the resonant frequency. The VCO will increase frequency until the desired RMS current is reached.

author: akhi
author_rank: Newbie
timestamp: August 22, 2023, 12:12:42 pm
content: Quote from: jonpaul on August 21, 2023, 11:02:32 pmNot sure to understandQuote from: jonpaul on August 21, 2023, 11:02:32 pmFor clarification there are two loads:- first is the load of the resonant converter: it is a daughter board supplied with a constant current (because of the primary side current regulation)- the second load is the one supplied by the daughter board.Since the daughter board rectify the current to produce a fixed DC voltage the power is always the same whatever the daughter board is loaded or not.So, the watts throughput of the resonant converter varies in accordance of daughter board numbers: max (12V: 50W*4, 10V: 10W*10, 5V: 20W*5)=400W and as min (12V: 50W*1, 10V: 10W*1, 5V: 20W*1)=70WQuote from: jonpaul on August 21, 2023, 11:02:32 pmWhat are the other typologies you are thinking about?

author: jonpaul
author_rank: Super Contributor
timestamp: August 23, 2023, 01:25:14 am
content: Bonjour cher Monsieur, j'ai vu que vous ettes francais!Restricting your design to resonant mode CS is permature, suggest that you first expore simpler topolgies.1/ The post input and output are not clear for power, voltage and desired regulation of current or voltage on loads.2/ Hard to see any logic in seties loads fed with CC.3/ we use parallel voltage source not series with appropriate separate trandfoemr wdgs.4/ Virtually any toplogy can work, foward, flyback, double fwd, etc.No need or benefit to resonant unluess very small size is needed.4/ Modern day switches are efficient and can be drivern in PWM etc at high swithc rates.Bon chanceJon