13.56MHz antenna full bridge rectifier (no voltage)

Hi guys,

I'm currently working on a wireless power transfer project. I've problem with the receiving end of the power transfer.

I'm using 1N4005 rectifier diode for the full bridge rectifier with smoothing capacitor(1uF) the o/p is about 10v dc . However, after putting an actual load ie blub or dc motor I got 0 dc voltage across it. But it's able to light up LED

I have tried impedance matching between antenna and load.

Changing smoothing capacitor to a larger and smaller one but it doesn't work

Please let me know if there is any problem with those configuration.

Thank you.

1N4005 is good up to a few hunderd Hz, not for 13,560,000 Hz !

You need a rectifier with MUCH faster switching characteristics and lower capacitance. The data sheets characterize the 1N4005 at 120Hz.

Brian.

Brain, thanks for your reply. Using 1n4005 I'm still able to get decent 10v O/P from the rectification. What I'm concern is that after putting an load I'm getting 0v from from it. Could it be low power that antenna is receiving?

1N4005 has junction capacitance around 10pF, which gives ~1.2kOhm reactance at 13.56MHz. That should not cause total failure.

I think you just don't get enough power from the receiver loop.

Besides junction capacitance, 1N400x has a huge problem with reverse recovery time when actually carrying fastly switched currents. Although a large percentage of input power would be burned in the diode, there should be still some rectifier output.

I would like to see output power from the receiver with a directly conncted resistive load to prove the matching.

Even if it had ~1.2K reactance, and ignoring factors like recovery time, when followed by 1uF (theoretical) reactance of ~0.01 Ohms the implication would be the voltage from the antenna to recover 10V was 1.2MV (Mega Volts) which I find hard to believe. Obviously there are other factors than pure capacitive division but the figures are unrealistic. Being in a bridge configuration further complicates matters.

I might expect 10V when using suitable rectifiers and feeding it directly from a transmittter output but not from an antenna. There are too many losses to recover usable power unless the field strength is very strong. The theory may sound good but it has little practical use.

Brian.

betwixt said:

Even if it had ~1.2K reactance, and ignoring factors like recovery time, when followed by 1uF (theoretical) reactance of ~0.01 Ohms the implication would be the voltage from the antenna to recover 10V was 1.2MV (Mega Volts) which I find hard to believe.

Click to expand...

Brian, I don't get you math here. Capacitance across the junction isn't source impedance.

betwixt said:

I might expect 10V when using suitable rectifiers and feeding it directly from a transmittter output but not from an antenna.

Click to expand...

The OP mentioned this is a wireless power transfer project, so we can expect tight inductive coupling to the excitation loop with RF power source.

I have to correct my statement "there should be still some rectifier output" with 1N400x. According to a SPICE simulation with a hopefully correct model, the output voltage is effectively collapsing above a few MHz input frequency, due to TT parameter working.

Hi guys,

Thanks for your reply. How do I improve the power transfer to the from the transmitting to the receiving. ie the circuit receiving circuit w/o the full bridge rectifier.

I was going to suggest that you remove the full diode bridge, and avoid the two diode voltage drops.
Instead put a small bulb for the load. Anything that works on AC. Possibly two led's, anti-parallel. They might light, if your secondary can produce as little as 1 or 2 mA.

You need to match impedance, if you are to obtain maximum power transfer. An led carrying 2 mA at 1.7V, has 850 ohms impedance. Therefore you should make your secondary so it has 850 ohms impedance (or say in a range between 50 and 200 percent of that), at your frequency of operation.

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However since the frequency is 13 MHz, led's may not work.

An alternative source is AM broadcast waves from a nearby radio antenna. 530 to 1700 kHz. They're able to power battery-less crystal radio sets from miles away.

My comment about capacitance was to show it isn't the only, or even the primary reason it will not work. That diode simply will not rectify a signal with 73nS period.

Brian.