The servos used in DLG/HLG are getting faster, stronger and more powerful all the time. More power output also means that the radio setup also needs more power to utilize the full performance of the system. The biggest concern is if the servos can draw so much power that the battery solution is unable to supply it. If this happens the voltage will drop, and the radio can no longer sustain operation.
Several scenarios can cause these severe currents peaks. Among the most common is a high speed approach to the landing field and a sudden application of breaking flaps, but also the sudden short circuit of a servo in flight. Unfortunately it happens far too often that a servo dies while flying and in this situation you want a power system that is able to deliver a huge amount of power very fast in order to burn off the short circuit as rapidly as possible and thereby keeping the system alive instead of shutting down due to overcurrent. After all it is better to land with only one aileron servo, than crashing without radio control.
LiPo is a good candidate for the battery, since the capacity/weight ratio is high, and internal resistance is very low compared to other types. But unfortunately the voltage is of a LiPo cells are not really compatible to many servos and receivers, so voltage regulation is therefore needed.
|Stepup Switching regulator
||Stepdown Switching regulator
||Linear Regulator IC
||Analog Linear Regulation loop
Based on the table above the obvious answer for high current systems is an analog build regulation loop. We spend countless hours doing simulations, prototypes and field test, before we finalized the design. We optimized the regulation loop to be as fast reacting and precise as possible.
TECHGIO F3K REGULATOR
While the design itself is a secret we keep to ourselves, we don’t mind showing the capabilities of the design.
To benchmark our F3K-regulator we made a comparison test with a linear regulator system based on 2 x L4941 regulators. These regulators are commonly found in small/medium powered brushless regulators. According to the specification of the brushless regulator, this system will handle 3A loads. The response from the regulator IC’s will be identical to all types of current limited systems. This means that in many ways, a switchmode regulator will perform in a similar manner as the linear regulator IC’s.
STANDARD 3A BEC ON BRUSHLESS MOTORCONTROLLER
As the first test, we made a stepload of 5A for 20sec. Both systems are initially loaded with 100mA and then shifted to 5A within nanoseconds.
The green graph show the output voltage across the load of our TECHGIO F3K regulator, and the blue graph shows the output of the BEC, based on a standard IC solution.
5A STEPLOAD TEST
As the 5A load is applied, both systems drop rapidly in voltage, as they need to detect the change in current and react to the new conditions. Many receivers have a minimum voltage of 3.5V in order to sustain operation. However, the receiver also have some capacitance build into the system, so they will be able to handle voltage drops below 3.5 for some microseconds. For how long the receiver can handle an undervoltage condition will vary with brands and models. However, it will be safe to assume that all receivers can handle an undervoltage condition for at least 50uS. The TECHGIO F3K regulator drops down below 3.5V for 2uS and is back in full regulation within 5uS. The standard regulator drops down for 8uS and never returns to full voltage for the duration of the test. It settles at a steady voltage of 3.5V, which is just enough to sustain receiver operation.
Next, we went all in and tested with a 10A load for 7.5sec…. Why 7.5s? Well – we wanted to test for 10sec, but our load resistors started to overheat from dissipating more than 50W of power and we had to stop a little earlier in order not to burn the tester 🙂
10A STEPLOAD TEST
The TECHGIO F3K regulator drops below 3.5V for 3uS and is back in full regulation within 6uS. The standard IC-solution drops to 2V and never returns above 3.5V. After 2sec the standard regulators starts to shut off completely to allow for cooling before restarting their output.
We are very pleased with the high performance of the TECHGIO F3K regulator. The power capabilities are extremely high. The performance of the regulator is only limited by the maximum temperature of the components. Due to the extremely small form-factor, there a physical limit to how much power the system can dissipate continuously (hours of operation). The precise value for the upper limit of continues current is dependent on the ambient temperature, cooling limitations in the fuselage, and battery voltage. Instead of making promises that is only true in a laboratory, we decided to implement a temperature warning system that will inform the user if he needs to consider a better mounting position or a bit of cooling air.